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This paper presents a thorough numerical investigation focused on optimizing the efficiency of quantum-well intermediate-band solar cells (QW-IBSCs) based on III-nitride materials. The optimization strategy encompasses manipulating confinement potential energy, controlling hydrostatic pressure, adjusting compositions, and varying thickness. The built-in electric fields in (In, Ga)N alloys and heavy-hole levels are considered to enhance the results’ accuracy. The finite element method (FEM) and Python 3.8 are employed to numerically solve the Schrödinger equation within the effective mass theory framework. This study reveals that meticulous design can achieve a theoretical photovoltaic efficiency of quantum-well intermediate-band solar cells (QW-IBSCs) that surpasses the Shockley–Queisser limit. Moreover, reducing the thickness of the layers enhances the light-absorbing capacity and, therefore, contributes to efficiency improvement. Additionally, the shape of the confinement potential significantly influences the device’s performance. This work is critical for society, as it represents a significant advancement in sustainable energy solutions, holding the promise of enhancing both the efficiency and accessibility of solar power generation. Consequently, this research stands at the forefront of innovation, offering a tangible and impactful contribution toward a greener and more sustainable energy future., Dynamics of Micro and Nano Systems

This thesis explores the diverse optical properties manifested when light interacts with various materials, with an emphasis on circular polarization- and bandgaprelated phenomena. The studies in this work are centered around Mueller matrix spectroscopic ellipsometry, with the objective of synthesizing and characterizing nanostructured and high-quality thin films to expand our understanding of the optical properties arising from their underlying structure and electronic transitions, respectively. Papers I, II, and III of the research address the optical properties associated with circular polarization, emphasizing the importance of the morphology and structure of the sculptured thin films used. To clarify this, AlN-based chiral sculptured thin films are synthesized using glancing angle deposition and magnetron sputtering. The discussion explores the impact of different growth parameters on the morphology and crystal structure of the films. By examining these thin film samples, it is shown how their structure and crystallographic orientation can be designed to reflect narrow spectral bands of circularly polarized light at specific wavelengths. The research also tackles how thin films preferentially reflect one handedness of circularly polarized light over the other with a high degree of circular polarization. A combination of theoretical and experimental studies offers insights into the nuances of growth and light-material interactions, particularly in complex photonic structures. Papers IV and V investigate the optical properties that arise from electronic transitions in thin films, focusing on the complex dielectric function and optical bandgap phenomena. These properties are explored using high-quality single crystalline homogenous thin films of ZnGaO, grown using metal-organic chemical vapor deposition. Various formalisms to calculate bandgap values are evaluated for their precision and applicability. The modified Cody formalism stands out as the preferred choice, Detta arbete utforskar optiska egenskaper som manifesteras när ljus interagerar med olika material. Avhandlingens tonvikt ligger på generation av cirkulärpolariserat ljus samt bandgapsrelaterade egenskaper. Studierna är centrerade kring spektroskopisk Mueller-matrisellipsometri, med målet att syntetisera och karakterisera nanostrukturerade och högkvalitativa tunna filmer. Detta för att utöka förståelsen av de optiska fenomen som uppstår från deras underliggande struktur respektive elektroniska övergångar. Artikel I, II och III i avhandlingen är relaterade till optiska polarisationsstudier och belyser betydelsen av morfologi och struktur hos optiska och fotoniska material. För att studera detta syntetiserar vi AlN baserade kirala skulpterade tunna filmer med hjälp av magnetronsputtring vid små infallsvinklar (glancing angle deposition) och diskuterar inverkan av olika tillväxtparametrar på filmernas morfologi och kristallstruktur. Genom att studera detta visar vi hur struktur och kristallografiska orientering kan skräddarsys för att reflektera smala spektrala band av där ljuset har hög grad av cirkulär polarisation. Vi visar även hur de tunna filmerna selektivt reflekterar den ena polarisationsriktningen (vänster/höger) beroende på det inkommande ljusets infallsvinkel och våglängd. Genom en serie teoretiska och experimentella studier ger vi detaljerad insikt i hur de studerade nanostrukturerna samverkar med ljus. Artikel IV och V undersöker de optiska egenskaperna som härrör från elektroniska övergångar i tunna filmer, med fokus specifikt på dielektricitetsfunktionen och optiska bandgapsfenomen. Dessa egenskaper studeras med för högkvalitativa enkristallina och homogena tunna filmer av ZnGaO, syntetiserade med metallorganisk CVD-teknik (Chemical Vapour Deposition). Vi utvärderar olika formalismer för att beräkna bandgapsvärden och bedömer deras noggrannhet och tillämpbarhet. Den modifierade Cody formalismen framhålls som bästa val på grund av dess egenskap att tillha, Funding agencies: This work was funded by Nanyang Technological University and Linköping University joint Ph.D. programme on Materials and Nanoscience Engineering (DnrLiU-2015-01061), Vetenskapsrådet (2018-04198), Stiftelsen för Strategisk Forskning (2009-00971), Energimyndigheten (grant number 46658-1), Stiftelsen Olle Engkvist Byggmästare (grant number 197-0210), and Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University (Faculty Grant SFO-Mat-LiU 2009-00971).

The transition to energy efficient smart grid and wireless communication with improved capacity require the development and optimization of next generation semiconductor technologies and electronic device components. Indium nitride (InN), gallium nitride (GaN) and aluminum nitride (AlN) compounds and their alloys are direct bandgap semiconductors with bandgap energies ranging from 0.7 to 6.0 eV, facilitating their utilization in optoelectronics and photonics. The GaN-based blue light-emitting diodes (LEDs) have enabled efficient and energy saving lighting, for which the Nobel Prize in Physics 2014 was awarded. GaN and AlN have high critical electric fields, high saturation carrier velocities and high thermal conductivities, which make them promising candidates for replacing silicon (Si) in next-generation power devices. The polarization-induced two-dimensional electron gas (2DEG), formed at the interface of AlGaN and GaN has enabled GaN-based high electron mobility transistors (HEMTs). These devices are suitable for high-power (HP) switching, power amplification and high-frequency (HF) applications in the millimeter-wave range up to THz frequencies. As such, HEMTs are suitable for next-generation 5G and 6G communication systems, radars, satellites, and a plethora of other related applications. Despite the immense efforts in the field, several material related issues still hinder the full exploitation of the unique properties of GaN-based semiconductors in HF and HP electronic applications. These limitations and challenges are related among others to: i) poor efficiency of p-type doping in GaN, ii) lack of linearity in AlGaN/GaN HEMTs used in low-noise RF amplifiers and, iii) MOCVD growth related difficulties in achieving ultra-thin and high Alcontent AlGaN barrier layers with compositionally sharp Al profiles in AlGaN/GaN HEMTs for HF applications. In this PhD thesis, we address the abovementioned issues by exploiting the hot-wall MOCVD combined with extensive mater, Funding agencies: The Swedish Governmental Agency for Innovation Systems (VINNOVA) under the Competence Center Program Grant No. 2016-05190 and 2022-03139, Linköping University, Chalmers University of Technology, Ericsson, Epiluvac, FMV, Gotmic, Hexagem, Hitachi Energy, On Semiconductor, Region Skåne, Saab, SweGaN, UMS, and Volvo cars. We further acknowledge support from the Swedish Research Council VR under Award No. 2016-00889 and 2022-04812, Swedish Foundation for Strategic Research under Grants No. RIF14-055 and No. EM16-0024, and the Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University, Faculty Grant SFO Mat LiU No. 2009-00971. The KAW Foundation is also acknowledged for support of the Linköping Electron Microscopy Laboratory.

This computational investigation delves into the electronic and optical attributes of InGaN/GaN nanostructures subjected to both harmonic and anharmonic confinement potentials, coupled with the influence of a nonresonant intense laser field (ILF). The theoretical framework incorporates higher-order anharmonic terms, specifically quartic and sextic terms. The solutions to the Schrödinger equation have been computed employing the finite element method and the effective mass theory. Moreover, linear and third-order nonlinear optical absorption coefficients are derived via a density matrix expansion. Our analysis reveals the feasibility of manipulating electronic and optical properties by adjusting confinement potential parameters, system attributes, and laser field intensity. In addition, the ILF induces remarkable modifications, characterized by reduced resonance peak amplitudes and a blue shift in absorption coefficients. Intriguingly, regardless of potential harmonicity, the impact of incident electromagnetic intensity is notably more pronounced in the absence of the ILF. These findings hold significant promise for advancing theoretical predictions, providing valuable insights into the intricate interplay between confinement potentials, laser fields, and their effects on electronic and optical behaviors within nanostructures., Dynamics of Micro and Nano Systems

This thesis explores the diverse optical properties manifested when light interacts with various materials, with an emphasis on circular polarization- and bandgaprelated phenomena. The studies in this work are centered around Mueller matrix spectroscopic ellipsometry, with the objective of synthesizing and characterizing nanostructured and high-quality thin films to expand our understanding of the optical properties arising from their underlying structure and electronic transitions, respectively. Papers I, II, and III of the research address the optical properties associated with circular polarization, emphasizing the importance of the morphology and structure of the sculptured thin films used. To clarify this, AlN-based chiral sculptured thin films are synthesized using glancing angle deposition and magnetron sputtering. The discussion explores the impact of different growth parameters on the morphology and crystal structure of the films. By examining these thin film samples, it is shown how their structure and crystallographic orientation can be designed to reflect narrow spectral bands of circularly polarized light at specific wavelengths. The research also tackles how thin films preferentially reflect one handedness of circularly polarized light over the other with a high degree of circular polarization. A combination of theoretical and experimental studies offers insights into the nuances of growth and light-material interactions, particularly in complex photonic structures. Papers IV and V investigate the optical properties that arise from electronic transitions in thin films, focusing on the complex dielectric function and optical bandgap phenomena. These properties are explored using high-quality single crystalline homogenous thin films of ZnGaO, grown using metal-organic chemical vapor deposition. Various formalisms to calculate bandgap values are evaluated for their precision and applicability. The modified Cody formalism stands out as the preferred choice, Detta arbete utforskar optiska egenskaper som manifesteras när ljus interagerar med olika material. Avhandlingens tonvikt ligger på generation av cirkulärpolariserat ljus samt bandgapsrelaterade egenskaper. Studierna är centrerade kring spektroskopisk Mueller-matrisellipsometri, med målet att syntetisera och karakterisera nanostrukturerade och högkvalitativa tunna filmer. Detta för att utöka förståelsen av de optiska fenomen som uppstår från deras underliggande struktur respektive elektroniska övergångar. Artikel I, II och III i avhandlingen är relaterade till optiska polarisationsstudier och belyser betydelsen av morfologi och struktur hos optiska och fotoniska material. För att studera detta syntetiserar vi AlN baserade kirala skulpterade tunna filmer med hjälp av magnetronsputtring vid små infallsvinklar (glancing angle deposition) och diskuterar inverkan av olika tillväxtparametrar på filmernas morfologi och kristallstruktur. Genom att studera detta visar vi hur struktur och kristallografiska orientering kan skräddarsys för att reflektera smala spektrala band av där ljuset har hög grad av cirkulär polarisation. Vi visar även hur de tunna filmerna selektivt reflekterar den ena polarisationsriktningen (vänster/höger) beroende på det inkommande ljusets infallsvinkel och våglängd. Genom en serie teoretiska och experimentella studier ger vi detaljerad insikt i hur de studerade nanostrukturerna samverkar med ljus. Artikel IV och V undersöker de optiska egenskaperna som härrör från elektroniska övergångar i tunna filmer, med fokus specifikt på dielektricitetsfunktionen och optiska bandgapsfenomen. Dessa egenskaper studeras med för högkvalitativa enkristallina och homogena tunna filmer av ZnGaO, syntetiserade med metallorganisk CVD-teknik (Chemical Vapour Deposition). Vi utvärderar olika formalismer för att beräkna bandgapsvärden och bedömer deras noggrannhet och tillämpbarhet. Den modifierade Cody formalismen framhålls som bästa val på grund av dess egenskap att tillha, Funding agencies: This work was funded by Nanyang Technological University and Linköping University joint Ph.D. programme on Materials and Nanoscience Engineering (DnrLiU-2015-01061), Vetenskapsrådet (2018-04198), Stiftelsen för Strategisk Forskning (2009-00971), Energimyndigheten (grant number 46658-1), Stiftelsen Olle Engkvist Byggmästare (grant number 197-0210), and Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University (Faculty Grant SFO-Mat-LiU 2009-00971).

The transition to energy efficient smart grid and wireless communication with improved capacity require the development and optimization of next generation semiconductor technologies and electronic device components. Indium nitride (InN), gallium nitride (GaN) and aluminum nitride (AlN) compounds and their alloys are direct bandgap semiconductors with bandgap energies ranging from 0.7 to 6.0 eV, facilitating their utilization in optoelectronics and photonics. The GaN-based blue light-emitting diodes (LEDs) have enabled efficient and energy saving lighting, for which the Nobel Prize in Physics 2014 was awarded. GaN and AlN have high critical electric fields, high saturation carrier velocities and high thermal conductivities, which make them promising candidates for replacing silicon (Si) in next-generation power devices. The polarization-induced two-dimensional electron gas (2DEG), formed at the interface of AlGaN and GaN has enabled GaN-based high electron mobility transistors (HEMTs). These devices are suitable for high-power (HP) switching, power amplification and high-frequency (HF) applications in the millimeter-wave range up to THz frequencies. As such, HEMTs are suitable for next-generation 5G and 6G communication systems, radars, satellites, and a plethora of other related applications. Despite the immense efforts in the field, several material related issues still hinder the full exploitation of the unique properties of GaN-based semiconductors in HF and HP electronic applications. These limitations and challenges are related among others to: i) poor efficiency of p-type doping in GaN, ii) lack of linearity in AlGaN/GaN HEMTs used in low-noise RF amplifiers and, iii) MOCVD growth related difficulties in achieving ultra-thin and high Alcontent AlGaN barrier layers with compositionally sharp Al profiles in AlGaN/GaN HEMTs for HF applications. In this PhD thesis, we address the abovementioned issues by exploiting the hot-wall MOCVD combined with extensive mater, Funding agencies: The Swedish Governmental Agency for Innovation Systems (VINNOVA) under the Competence Center Program Grant No. 2016-05190 and 2022-03139, Linköping University, Chalmers University of Technology, Ericsson, Epiluvac, FMV, Gotmic, Hexagem, Hitachi Energy, On Semiconductor, Region Skåne, Saab, SweGaN, UMS, and Volvo cars. We further acknowledge support from the Swedish Research Council VR under Award No. 2016-00889 and 2022-04812, Swedish Foundation for Strategic Research under Grants No. RIF14-055 and No. EM16-0024, and the Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University, Faculty Grant SFO Mat LiU No. 2009-00971. The KAW Foundation is also acknowledged for support of the Linköping Electron Microscopy Laboratory.

This thesis explores the diverse optical properties manifested when light interacts with various materials, with an emphasis on circular polarization- and bandgaprelated phenomena. The studies in this work are centered around Mueller matrix spectroscopic ellipsometry, with the objective of synthesizing and characterizing nanostructured and high-quality thin films to expand our understanding of the optical properties arising from their underlying structure and electronic transitions, respectively. Papers I, II, and III of the research address the optical properties associated with circular polarization, emphasizing the importance of the morphology and structure of the sculptured thin films used. To clarify this, AlN-based chiral sculptured thin films are synthesized using glancing angle deposition and magnetron sputtering. The discussion explores the impact of different growth parameters on the morphology and crystal structure of the films. By examining these thin film samples, it is shown how their structure and crystallographic orientation can be designed to reflect narrow spectral bands of circularly polarized light at specific wavelengths. The research also tackles how thin films preferentially reflect one handedness of circularly polarized light over the other with a high degree of circular polarization. A combination of theoretical and experimental studies offers insights into the nuances of growth and light-material interactions, particularly in complex photonic structures. Papers IV and V investigate the optical properties that arise from electronic transitions in thin films, focusing on the complex dielectric function and optical bandgap phenomena. These properties are explored using high-quality single crystalline homogenous thin films of ZnGaO, grown using metal-organic chemical vapor deposition. Various formalisms to calculate bandgap values are evaluated for their precision and applicability. The modified Cody formalism stands out as the preferred choice, Detta arbete utforskar optiska egenskaper som manifesteras när ljus interagerar med olika material. Avhandlingens tonvikt ligger på generation av cirkulärpolariserat ljus samt bandgapsrelaterade egenskaper. Studierna är centrerade kring spektroskopisk Mueller-matrisellipsometri, med målet att syntetisera och karakterisera nanostrukturerade och högkvalitativa tunna filmer. Detta för att utöka förståelsen av de optiska fenomen som uppstår från deras underliggande struktur respektive elektroniska övergångar. Artikel I, II och III i avhandlingen är relaterade till optiska polarisationsstudier och belyser betydelsen av morfologi och struktur hos optiska och fotoniska material. För att studera detta syntetiserar vi AlN baserade kirala skulpterade tunna filmer med hjälp av magnetronsputtring vid små infallsvinklar (glancing angle deposition) och diskuterar inverkan av olika tillväxtparametrar på filmernas morfologi och kristallstruktur. Genom att studera detta visar vi hur struktur och kristallografiska orientering kan skräddarsys för att reflektera smala spektrala band av där ljuset har hög grad av cirkulär polarisation. Vi visar även hur de tunna filmerna selektivt reflekterar den ena polarisationsriktningen (vänster/höger) beroende på det inkommande ljusets infallsvinkel och våglängd. Genom en serie teoretiska och experimentella studier ger vi detaljerad insikt i hur de studerade nanostrukturerna samverkar med ljus. Artikel IV och V undersöker de optiska egenskaperna som härrör från elektroniska övergångar i tunna filmer, med fokus specifikt på dielektricitetsfunktionen och optiska bandgapsfenomen. Dessa egenskaper studeras med för högkvalitativa enkristallina och homogena tunna filmer av ZnGaO, syntetiserade med metallorganisk CVD-teknik (Chemical Vapour Deposition). Vi utvärderar olika formalismer för att beräkna bandgapsvärden och bedömer deras noggrannhet och tillämpbarhet. Den modifierade Cody formalismen framhålls som bästa val på grund av dess egenskap att tillha, Funding agencies: This work was funded by Nanyang Technological University and Linköping University joint Ph.D. programme on Materials and Nanoscience Engineering (DnrLiU-2015-01061), Vetenskapsrådet (2018-04198), Stiftelsen för Strategisk Forskning (2009-00971), Energimyndigheten (grant number 46658-1), Stiftelsen Olle Engkvist Byggmästare (grant number 197-0210), and Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University (Faculty Grant SFO-Mat-LiU 2009-00971).

The transition to energy efficient smart grid and wireless communication with improved capacity require the development and optimization of next generation semiconductor technologies and electronic device components. Indium nitride (InN), gallium nitride (GaN) and aluminum nitride (AlN) compounds and their alloys are direct bandgap semiconductors with bandgap energies ranging from 0.7 to 6.0 eV, facilitating their utilization in optoelectronics and photonics. The GaN-based blue light-emitting diodes (LEDs) have enabled efficient and energy saving lighting, for which the Nobel Prize in Physics 2014 was awarded. GaN and AlN have high critical electric fields, high saturation carrier velocities and high thermal conductivities, which make them promising candidates for replacing silicon (Si) in next-generation power devices. The polarization-induced two-dimensional electron gas (2DEG), formed at the interface of AlGaN and GaN has enabled GaN-based high electron mobility transistors (HEMTs). These devices are suitable for high-power (HP) switching, power amplification and high-frequency (HF) applications in the millimeter-wave range up to THz frequencies. As such, HEMTs are suitable for next-generation 5G and 6G communication systems, radars, satellites, and a plethora of other related applications. Despite the immense efforts in the field, several material related issues still hinder the full exploitation of the unique properties of GaN-based semiconductors in HF and HP electronic applications. These limitations and challenges are related among others to: i) poor efficiency of p-type doping in GaN, ii) lack of linearity in AlGaN/GaN HEMTs used in low-noise RF amplifiers and, iii) MOCVD growth related difficulties in achieving ultra-thin and high Alcontent AlGaN barrier layers with compositionally sharp Al profiles in AlGaN/GaN HEMTs for HF applications. In this PhD thesis, we address the abovementioned issues by exploiting the hot-wall MOCVD combined with extensive mater, Funding agencies: The Swedish Governmental Agency for Innovation Systems (VINNOVA) under the Competence Center Program Grant No. 2016-05190 and 2022-03139, Linköping University, Chalmers University of Technology, Ericsson, Epiluvac, FMV, Gotmic, Hexagem, Hitachi Energy, On Semiconductor, Region Skåne, Saab, SweGaN, UMS, and Volvo cars. We further acknowledge support from the Swedish Research Council VR under Award No. 2016-00889 and 2022-04812, Swedish Foundation for Strategic Research under Grants No. RIF14-055 and No. EM16-0024, and the Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University, Faculty Grant SFO Mat LiU No. 2009-00971. The KAW Foundation is also acknowledged for support of the Linköping Electron Microscopy Laboratory.

This thesis explores the diverse optical properties manifested when light interacts with various materials, with an emphasis on circular polarization- and bandgaprelated phenomena. The studies in this work are centered around Mueller matrix spectroscopic ellipsometry, with the objective of synthesizing and characterizing nanostructured and high-quality thin films to expand our understanding of the optical properties arising from their underlying structure and electronic transitions, respectively. Papers I, II, and III of the research address the optical properties associated with circular polarization, emphasizing the importance of the morphology and structure of the sculptured thin films used. To clarify this, AlN-based chiral sculptured thin films are synthesized using glancing angle deposition and magnetron sputtering. The discussion explores the impact of different growth parameters on the morphology and crystal structure of the films. By examining these thin film samples, it is shown how their structure and crystallographic orientation can be designed to reflect narrow spectral bands of circularly polarized light at specific wavelengths. The research also tackles how thin films preferentially reflect one handedness of circularly polarized light over the other with a high degree of circular polarization. A combination of theoretical and experimental studies offers insights into the nuances of growth and light-material interactions, particularly in complex photonic structures. Papers IV and V investigate the optical properties that arise from electronic transitions in thin films, focusing on the complex dielectric function and optical bandgap phenomena. These properties are explored using high-quality single crystalline homogenous thin films of ZnGaO, grown using metal-organic chemical vapor deposition. Various formalisms to calculate bandgap values are evaluated for their precision and applicability. The modified Cody formalism stands out as the preferred choice, Detta arbete utforskar optiska egenskaper som manifesteras när ljus interagerar med olika material. Avhandlingens tonvikt ligger på generation av cirkulärpolariserat ljus samt bandgapsrelaterade egenskaper. Studierna är centrerade kring spektroskopisk Mueller-matrisellipsometri, med målet att syntetisera och karakterisera nanostrukturerade och högkvalitativa tunna filmer. Detta för att utöka förståelsen av de optiska fenomen som uppstår från deras underliggande struktur respektive elektroniska övergångar. Artikel I, II och III i avhandlingen är relaterade till optiska polarisationsstudier och belyser betydelsen av morfologi och struktur hos optiska och fotoniska material. För att studera detta syntetiserar vi AlN baserade kirala skulpterade tunna filmer med hjälp av magnetronsputtring vid små infallsvinklar (glancing angle deposition) och diskuterar inverkan av olika tillväxtparametrar på filmernas morfologi och kristallstruktur. Genom att studera detta visar vi hur struktur och kristallografiska orientering kan skräddarsys för att reflektera smala spektrala band av där ljuset har hög grad av cirkulär polarisation. Vi visar även hur de tunna filmerna selektivt reflekterar den ena polarisationsriktningen (vänster/höger) beroende på det inkommande ljusets infallsvinkel och våglängd. Genom en serie teoretiska och experimentella studier ger vi detaljerad insikt i hur de studerade nanostrukturerna samverkar med ljus. Artikel IV och V undersöker de optiska egenskaperna som härrör från elektroniska övergångar i tunna filmer, med fokus specifikt på dielektricitetsfunktionen och optiska bandgapsfenomen. Dessa egenskaper studeras med för högkvalitativa enkristallina och homogena tunna filmer av ZnGaO, syntetiserade med metallorganisk CVD-teknik (Chemical Vapour Deposition). Vi utvärderar olika formalismer för att beräkna bandgapsvärden och bedömer deras noggrannhet och tillämpbarhet. Den modifierade Cody formalismen framhålls som bästa val på grund av dess egenskap att tillha, Funding agencies: This work was funded by Nanyang Technological University and Linköping University joint Ph.D. programme on Materials and Nanoscience Engineering (DnrLiU-2015-01061), Vetenskapsrådet (2018-04198), Stiftelsen för Strategisk Forskning (2009-00971), Energimyndigheten (grant number 46658-1), Stiftelsen Olle Engkvist Byggmästare (grant number 197-0210), and Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University (Faculty Grant SFO-Mat-LiU 2009-00971).

The transition to energy efficient smart grid and wireless communication with improved capacity require the development and optimization of next generation semiconductor technologies and electronic device components. Indium nitride (InN), gallium nitride (GaN) and aluminum nitride (AlN) compounds and their alloys are direct bandgap semiconductors with bandgap energies ranging from 0.7 to 6.0 eV, facilitating their utilization in optoelectronics and photonics. The GaN-based blue light-emitting diodes (LEDs) have enabled efficient and energy saving lighting, for which the Nobel Prize in Physics 2014 was awarded. GaN and AlN have high critical electric fields, high saturation carrier velocities and high thermal conductivities, which make them promising candidates for replacing silicon (Si) in next-generation power devices. The polarization-induced two-dimensional electron gas (2DEG), formed at the interface of AlGaN and GaN has enabled GaN-based high electron mobility transistors (HEMTs). These devices are suitable for high-power (HP) switching, power amplification and high-frequency (HF) applications in the millimeter-wave range up to THz frequencies. As such, HEMTs are suitable for next-generation 5G and 6G communication systems, radars, satellites, and a plethora of other related applications. Despite the immense efforts in the field, several material related issues still hinder the full exploitation of the unique properties of GaN-based semiconductors in HF and HP electronic applications. These limitations and challenges are related among others to: i) poor efficiency of p-type doping in GaN, ii) lack of linearity in AlGaN/GaN HEMTs used in low-noise RF amplifiers and, iii) MOCVD growth related difficulties in achieving ultra-thin and high Alcontent AlGaN barrier layers with compositionally sharp Al profiles in AlGaN/GaN HEMTs for HF applications. In this PhD thesis, we address the abovementioned issues by exploiting the hot-wall MOCVD combined with extensive mater, Funding agencies: The Swedish Governmental Agency for Innovation Systems (VINNOVA) under the Competence Center Program Grant No. 2016-05190 and 2022-03139, Linköping University, Chalmers University of Technology, Ericsson, Epiluvac, FMV, Gotmic, Hexagem, Hitachi Energy, On Semiconductor, Region Skåne, Saab, SweGaN, UMS, and Volvo cars. We further acknowledge support from the Swedish Research Council VR under Award No. 2016-00889 and 2022-04812, Swedish Foundation for Strategic Research under Grants No. RIF14-055 and No. EM16-0024, and the Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University, Faculty Grant SFO Mat LiU No. 2009-00971. The KAW Foundation is also acknowledged for support of the Linköping Electron Microscopy Laboratory.

Post the commercialization and widespread use in light emitting diodes (LEDs), heterostructures of III-nitride semiconductors (GaN, AlN, InN, and BN) with their alloys, have shown immense promise in applications not limited to optoelectronics, but ranging from high power and high frequency electronics to plasmonics, sensor technology and quantum computing. While the superior properties of electrons and the two-dimensional electron gas (2DEG) have peaked a great deal of attention on this materials system, similar levels of advancements in p-type III-nitrides are required to tap into the complete benefits this semiconductor family can potentially provide. Like in most other wide-bandgap materials, the poor performance of p-type material in III-nitrides has led to only a few studies reported on p-channel III-nitride electronic devices. The use of p-type superlattice (SL) is valuable for III-nitride semiconductor-based p-channel Field effect transistors (pFETs) and LEDs because the polarization effects create a periodic oscillation of the energy bands, enhancing the ionization of the deep acceptors. Thus, the use of Mg-doped GaN/AlGaN SL is a pathway to get high hole concentration and mobility simultaneously, and pFETs engineered around a GaN/AlGaN SL have demonstrated record electrical performance. The present study will systematically explore the electrical properties of epitaxially grown p-type Ga-polar and N-polar, modulation doped and uniformly doped GaN/AlGaN, and GaN/AlN/AlGaN superlattices (grown using the MOCVD growth technique). Following this, the discovery of a novel acceptor trap, proposed at 0.8 eV above the valence band of GaN, will be presented with simulations and experiments. The implications of this trap level, and its impact as the source of holes in dopant-deficient systems will be elucidated. This study will also explain in detail how charge balance is achieved in recent p-channel III-nitride electronic and optoelectronic devices. A detailed method

Post the commercialization and widespread use in light emitting diodes (LEDs), heterostructures of III-nitride semiconductors (GaN, AlN, InN, and BN) with their alloys, have shown immense promise in applications not limited to optoelectronics, but ranging from high power and high frequency electronics to plasmonics, sensor technology and quantum computing. While the superior properties of electrons and the two-dimensional electron gas (2DEG) have peaked a great deal of attention on this materials system, similar levels of advancements in p-type III-nitrides are required to tap into the complete benefits this semiconductor family can potentially provide. Like in most other wide-bandgap materials, the poor performance of p-type material in III-nitrides has led to only a few studies reported on p-channel III-nitride electronic devices. The use of p-type superlattice (SL) is valuable for III-nitride semiconductor-based p-channel Field effect transistors (pFETs) and LEDs because the polarization effects create a periodic oscillation of the energy bands, enhancing the ionization of the deep acceptors. Thus, the use of Mg-doped GaN/AlGaN SL is a pathway to get high hole concentration and mobility simultaneously, and pFETs engineered around a GaN/AlGaN SL have demonstrated record electrical performance. The present study will systematically explore the electrical properties of epitaxially grown p-type Ga-polar and N-polar, modulation doped and uniformly doped GaN/AlGaN, and GaN/AlN/AlGaN superlattices (grown using the MOCVD growth technique). Following this, the discovery of a novel acceptor trap, proposed at 0.8 eV above the valence band of GaN, will be presented with simulations and experiments. The implications of this trap level, and its impact as the source of holes in dopant-deficient systems will be elucidated. This study will also explain in detail how charge balance is achieved in recent p-channel III-nitride electronic and optoelectronic devices. A detailed method

In the field of semiconductor devices, the III-nitride material system, which is mainly made up of Indium Nitride (InN), Gallium Nitride (GaN) and Aluminum Nitride (AlN), has seen a great deal of attention over the past decade. Despite the maturity of this field of research, the growth mechanics and physics that govern the behavior of these devices is still poorly understood. For all the devices mentioned, there exist regions called heterojunctions, which can be defined as the interface between two materials of different band gaps. In the case of LEDs, these heterojunctions are typically at the interface of alloy regions, which are the Quantum Well (QWs) layer and the Electron-Blocking Layer (EBL). These regions have compositional fluctuations due to the random distribution of the atomic constituent in the alloy. This phenomenon, known as alloy disorder, has largely been insignificant in the studies of other III-V semiconductors. However, due to the higher effective mass and larger band gaps of the nitrides, disorder plays a significant role in understanding the carrier transport behavior within nitride devices. My research involves examining each of these layers and studying the hole transport behavior within these two types of heterostructures to better understand their electrical behavior. However, typical studies use LEDs as test structures, which are bipolar devices and are subject to recombination mechanisms. By using unipolar heterostructures, we can focus solely on the carrier transport within these structures without recombination complicating the analysis of the system, making them ideal test vehicles for theoretical models. My study involves simulating a three-dimensional unipolar p-type heterostructure that incorporates the fluctuations of the alloy composition within the alloy region. This would normally require solving for the wavefunctions of the system via Schrödinger’s equation. However, solving this equation in 3D is a computationally expensive tas

Gallium nitride (GaN) and indium gallium nitride (InGaN) nanostructures, and their nanocomposites with reduced graphene oxide (rGO) are prepared by solvothermal method and used as sensing materials for ammonia gas. The ammonia sensing characteristics are studied by coating the synthesized GaN and InGaN nanostructures, and their nanocomposites on interdigitated electrodes. The sensing parameters, i.e., sensing response, selectivity, and stability, are studied for various operating temperatures and relative humidity. The pristine GaN and InGaN exhibit a sensing response of 23.8% and 28.1% for 200 ppm concentration at 300 K, whereas the nanocomposites of GaN and InGaN show an increased response of 37.4% and 44.2%. This improvement in the nanocomposites maybe ascribed to the better conductivity, higher number of gas adsorption sites and reduced bandgap. It is found that these materials are an excellent choice for ammonia gas sensing application., QC 20220615

У рукопису запропоновано метод моделювання і аналізу імпульсних та високочастотних властивостей багатодолинних напівпровідників. Модель застосовано до сучасних, актуальних і, як буде доведено у тому числі у рукописі, перспективних напівпровідникових матеріалів GaN, AlN і InN, які зараз все більше стають відомі під узагальнюючою назвою III-нітриди. Метод відрізняється можливістю застосування одночасно як для динамічних задач у часі, так і змінних у просторі полів та збалансованим використанням обчислювальних ресурсів без істотних втрат точності. Базисом запропонованого підходу є чисельне рішення системи диференціальних рівнянь, які отримані з кінетичного рівняння Больцмана у наближенні часу релаксації по функції розподілу у k-просторі. Ці рівняння відомі під узагальненою назвою релаксаційних. В англомовній літературі цей метод зустрічається під назвою «Method of moments» (метод моментів). Але на відміну від традиційного використання рівнянь для концентрації носіїв, їх імпульсу і енергії у праці використано замість рівняння релаксації енергії рівняння для електронної температури як міри середньої енергії тільки хаотичного руху. Друга принципова відмінність полягає в тому, що часи релаксації визначаються через усереднення квантовомеханічних швидкостей розсіювання, зазвичай використовуваних у методі Монте-Карло, для окремих видів розсіювання, а не як інтегральні значення із статичних характеристик матеріалу. Різні механізми розсіювання носіїв враховуються через специфічні для них часи релаксації за допомогою проведення усереднення за максвеллівською функцією розподілу в наближенні електронної температури. Система отриманих рівнянь включає рівняння у частинних похідних як за часом так і за координатами, що дає можливість дослідити характерні прояви імпульсних властивостей напівпровідникових матеріалів, зокрема: «балістичний транспорт» носіїв у просторі та ефект «сплеску» дрейфової швидкості у часі. Вперше розглянуто використання Фур’є-перетворення імпульсної залежності д

У рукопису запропоновано метод моделювання і аналізу імпульсних та високочастотних властивостей багатодолинних напівпровідників. Модель застосовано до сучасних, актуальних і, як буде доведено у тому числі у рукописі, перспективних напівпровідникових матеріалів GaN, AlN і InN, які зараз все більше стають відомі під узагальнюючою назвою III-нітриди. Метод відрізняється можливістю застосування одночасно як для динамічних задач у часі, так і змінних у просторі полів та збалансованим використанням обчислювальних ресурсів без істотних втрат точності. Базисом запропонованого підходу є чисельне рішення системи диференціальних рівнянь, які отримані з кінетичного рівняння Больцмана у наближенні часу релаксації по функції розподілу у k-просторі. Ці рівняння відомі під узагальненою назвою релаксаційних. В англомовній літературі цей метод зустрічається під назвою «Method of moments» (метод моментів). Але на відміну від традиційного використання рівнянь для концентрації носіїв, їх імпульсу і енергії у праці використано замість рівняння релаксації енергії рівняння для електронної температури як міри середньої енергії тільки хаотичного руху. Друга принципова відмінність полягає в тому, що часи релаксації визначаються через усереднення квантовомеханічних швидкостей розсіювання, зазвичай використовуваних у методі Монте-Карло, для окремих видів розсіювання, а не як інтегральні значення із статичних характеристик матеріалу. Різні механізми розсіювання носіїв враховуються через специфічні для них часи релаксації за допомогою проведення усереднення за максвеллівською функцією розподілу в наближенні електронної температури. Система отриманих рівнянь включає рівняння у частинних похідних як за часом так і за координатами, що дає можливість дослідити характерні прояви імпульсних властивостей напівпровідникових матеріалів, зокрема: «балістичний транспорт» носіїв у просторі та ефект «сплеску» дрейфової швидкості у часі. Вперше розглянуто використання Фур’є-перетворення імпульсної залежності д, The dissertation work proposed a method for modeling and interpreting the high-frequency characteristics of multi-valley semiconductors, in particular, GaN, AlN, and InN. The model is practiced to state-of-the-art, encouraging, and relevant materials GaN, AlN, and InN, which are now recognized under the generic name III-nitrides. The method is noticed by the economical use of computational resources without meaningful loss of accuracy and the feasibility of using both for dynamic tasks over time and variables in the scope of fields. The introduced approach is based on solving a system of differential equating, which are known as relaxation equations and are obtained from the Boltzmann kinetic equating in the relaxation time approximation by averaging over k-space. In English literature, this method is known as the "method of momentum." Indifference to the traditional system of equations for the concentration of carriers, their momentum, and energy, here, alternately of the energy relaxation equation, the equation for electron temperature is done as a measure of the energy of only chaotic movement. The second meaningful difference is that the relaxation times are not defined as integral values from the static properties of the material, but for averaging the quantum-mechanical scattering rates usually used in the Monte Carlo meth-od for particular types of scattering. The averaging was made over the Maxwell distribution function in the electron temperature approximation, as an outcome of which numerous mechanisms of carrier scattering through their explicit relaxation times are taken into account. Since the system of equations applied includes equations in partial derivatives concerning time and coordinates, it performs it possible to examine the characteristic demonstrations of the impulse properties of the mate-rials under consideration, particularly, the time effect of the “overshoot” of drift velocity and the spatial “ballistic transport” of carriers. For the fir

The thesis focuses on the gas flow profile optimization of a non-conventional injector in a hot-wall MOCVD system. The injector’s gas flow profile is simulated with CFD and demonstrates awell-behaved laminar flow with a parabolic profile. To ensure the theory is in coherence with the reality, a qualitative study with five thermocouples in a test graphite piece of the was performed. First the thesis will take you through an introduction of the semiconductor field to arrive in a problem formulation. Then you will read about the principles of MOCVD systems, fluid dynamics principles and thermocouple theory. The experiment’s way of approach is thendescribed through all steps from blue print to results. A discussion about the result and the conclusion will be read before the proposals of future work based on the thesis work. The laminar flow is confirmed according to the resulting data and the limitations of the system is set to two different cases depending on background temperature. At 1000 °C a laminar flow is strongly indicated to be obtained at position 3A, closest to the growth area, within the gas flow range of 25 SLM regardless of background pressure, except for 700 mBar indicating turbulent flow for 15 SLM an up. At 20 and 200 mBar the laminar flow limit is suggested by data to be even higher and reaching a value of 35 SLM. At 450 °C the data indicate a laminar flow up to 20 SLM at position 3A regardless of background pressure condition, except for 700 mBar where the data indicate a laminar flow at 35 and 40 SLM. 50 mBar strongly indicates a laminar flow profile up to a gas flow of 35 SLM. With a background pressure of 20 mBar, the data suggests a laminar flow profile up to at least 25 SLM. At 100 mBar the data indicates a laminar flow within the range of 30 SLM.

The thesis focuses on the gas flow profile optimization of a non-conventional injector in a hot-wall MOCVD system. The injector’s gas flow profile is simulated with CFD and demonstrates awell-behaved laminar flow with a parabolic profile. To ensure the theory is in coherence with the reality, a qualitative study with five thermocouples in a test graphite piece of the was performed. First the thesis will take you through an introduction of the semiconductor field to arrive in a problem formulation. Then you will read about the principles of MOCVD systems, fluid dynamics principles and thermocouple theory. The experiment’s way of approach is thendescribed through all steps from blue print to results. A discussion about the result and the conclusion will be read before the proposals of future work based on the thesis work. The laminar flow is confirmed according to the resulting data and the limitations of the system is set to two different cases depending on background temperature. At 1000 °C a laminar flow is strongly indicated to be obtained at position 3A, closest to the growth area, within the gas flow range of 25 SLM regardless of background pressure, except for 700 mBar indicating turbulent flow for 15 SLM an up. At 20 and 200 mBar the laminar flow limit is suggested by data to be even higher and reaching a value of 35 SLM. At 450 °C the data indicate a laminar flow up to 20 SLM at position 3A regardless of background pressure condition, except for 700 mBar where the data indicate a laminar flow at 35 and 40 SLM. 50 mBar strongly indicates a laminar flow profile up to a gas flow of 35 SLM. With a background pressure of 20 mBar, the data suggests a laminar flow profile up to at least 25 SLM. At 100 mBar the data indicates a laminar flow within the range of 30 SLM.

Vertical-cavity surface-emitting lasers (VCSELs) are a special class of laser diode that use top-side and bottom-side parallel mirrors to emit a laser beam vertically from the top surface, as compared to conventional edge-emitting lasers that emit light from the sides of the devices. Compared to edge-emitting lasers, VCSELs have many unique attributes, such as a low threshold current that leads to low power consumption, high-speed direct modulation, superior beam quality, and they can be easily arranged into two-dimensional VCSEL arrays for scalable power. This leads to several exciting applications; for example, VCSELs are the key component in the Apple iPhone X that enables Face ID, which allows users to securely unlock their devices simply by looking at their phones. However, the VCSEL market is currently limited to red-emitting and infrared-emitting VCSELs that use GaAs-based and InP-based systems. If shorter wavelength emitting VCSELs could be created, it would open up a whole new world of untapped and exciting applications. For example, blue and green VCSELs could be paired with red VCSELs to create next-generation display and projector technology. The low power consumption and high beam quality of VCSEL-based displays would be particularly promising for virtual and augmented reality systems. Shorter wavelength VCSELs can be created using GaN-based materials, but these devices have been very challenging to create. The first GaN-based VCSEL was demonstrated in 2008, and only eight research groups have demonstrated these devices over the following decade. With the first report in 2012, the University of California, Santa Barbara (UCSB) has been the only group in the United States to create GaN-based VCSELs. Compared to the c-plane GaN VCSELs from all of the other groups, VCSELs from UCSB have used m-plane GaN, which uniquely provides 100% polarized emission for both individual VCSELs and VCSEL arrays. The main problem with GaN VCSELs from UCSB has been their ina

High efficiency III-nitride light-emitting diodes (LEDs) have drastically improved solid-state lighting. They are sold in stores and are gradually replacing compact fluorescent lightbulbs because they use less power and last longer. III-nitrides are on the cusp of entering another market. As the size of mobile electronics shrink over time, display technologies must also move to smaller form factors while maintaining high efficiencies. To achieve these goals, III-nitride LEDs are once again a candidate to overtake the state of the art. Incumbent technologies, such as liquid crystal displays (LCDs) and organic LED (OLED) displays, have major issues with power efficiency. A new technology, termed the micro-LED (uLED) display, is poised to enter the market in the next few years. A uLED display is made of inorganic LEDs (such as InGaN or AlGaInP) with dimensions typically below 40 um. uLED displays are promising due to higher luminance (brightness) than OLEDs, wider viewing angles, and significantly higher energy efficiencies. In this thesis, advances in InGaN uLED epitaxial design, nanofabrication, and mass transfer are discussed. Chapter 1 introduces the III-V families (arsenides/phosphides/nitrides) and provides insight into uLED design. While the majority of IngaN uLEDs are grown on sapphire or silicon, there are many reasons to explore homoepitaxial growth on freestanding GaN (particularly on semipolar planes). Chapter 2 presents a comparison of external quantum efficiency (EQE) amongst various sized uLEDs and shows that high EQEs (40-45%) are sustained as the size of the uLED drops. Reasons for efficiency loss are presented and designs aimed at improving uLED efficiencies are highlighted. Chapter 3 discusses the incorporation of tunnel junction contacts to uLEDs to enable new design space (n-type mirrors and multiple active region growths). Chapter 4 examines ideas to eliminate the drop of efficiency with decreasing uLED size that incorporates a current aperture an

8-band k.p theory was applied to bulk GaN and InN. The optical transitionintensity was computed and results show > 80-90% degree of polarization inthe direction of compression. Polarization switching is observed when strainwas reversed from compressive to tensile. 6 band k.p theory was used tostudy InGaN quantum dot/GaN elliptical pyramid structures. The opticaltransition intensity was calculated for different elongations of the pyramid.Elongation of the pyramid gives rise to a small polarization in the directionof the pyramid elongation. The optical transition intensity was calculatedfor elongated quantum dots and was strongly in uencing the polarization inthe direction of the quantum dot elongation, with a degree of polarization of >90%.

High efficiency III-nitride light-emitting diodes (LEDs) have drastically improved solid-state lighting. They are sold in stores and are gradually replacing compact fluorescent lightbulbs because they use less power and last longer. III-nitrides are on the cusp of entering another market. As the size of mobile electronics shrink over time, display technologies must also move to smaller form factors while maintaining high efficiencies. To achieve these goals, III-nitride LEDs are once again a candidate to overtake the state of the art. Incumbent technologies, such as liquid crystal displays (LCDs) and organic LED (OLED) displays, have major issues with power efficiency. A new technology, termed the micro-LED (uLED) display, is poised to enter the market in the next few years. A uLED display is made of inorganic LEDs (such as InGaN or AlGaInP) with dimensions typically below 40 um. uLED displays are promising due to higher luminance (brightness) than OLEDs, wider viewing angles, and significantly higher energy efficiencies. In this thesis, advances in InGaN uLED epitaxial design, nanofabrication, and mass transfer are discussed. Chapter 1 introduces the III-V families (arsenides/phosphides/nitrides) and provides insight into uLED design. While the majority of IngaN uLEDs are grown on sapphire or silicon, there are many reasons to explore homoepitaxial growth on freestanding GaN (particularly on semipolar planes). Chapter 2 presents a comparison of external quantum efficiency (EQE) amongst various sized uLEDs and shows that high EQEs (40-45%) are sustained as the size of the uLED drops. Reasons for efficiency loss are presented and designs aimed at improving uLED efficiencies are highlighted. Chapter 3 discusses the incorporation of tunnel junction contacts to uLEDs to enable new design space (n-type mirrors and multiple active region growths). Chapter 4 examines ideas to eliminate the drop of efficiency with decreasing uLED size that incorporates a current aperture an

Vertical-cavity surface-emitting lasers (VCSELs) are a special class of laser diode that use top-side and bottom-side parallel mirrors to emit a laser beam vertically from the top surface, as compared to conventional edge-emitting lasers that emit light from the sides of the devices. Compared to edge-emitting lasers, VCSELs have many unique attributes, such as a low threshold current that leads to low power consumption, high-speed direct modulation, superior beam quality, and they can be easily arranged into two-dimensional VCSEL arrays for scalable power. This leads to several exciting applications; for example, VCSELs are the key component in the Apple iPhone X that enables Face ID, which allows users to securely unlock their devices simply by looking at their phones. However, the VCSEL market is currently limited to red-emitting and infrared-emitting VCSELs that use GaAs-based and InP-based systems. If shorter wavelength emitting VCSELs could be created, it would open up a whole new world of untapped and exciting applications. For example, blue and green VCSELs could be paired with red VCSELs to create next-generation display and projector technology. The low power consumption and high beam quality of VCSEL-based displays would be particularly promising for virtual and augmented reality systems. Shorter wavelength VCSELs can be created using GaN-based materials, but these devices have been very challenging to create. The first GaN-based VCSEL was demonstrated in 2008, and only eight research groups have demonstrated these devices over the following decade. With the first report in 2012, the University of California, Santa Barbara (UCSB) has been the only group in the United States to create GaN-based VCSELs. Compared to the c-plane GaN VCSELs from all of the other groups, VCSELs from UCSB have used m-plane GaN, which uniquely provides 100% polarized emission for both individual VCSELs and VCSEL arrays. The main problem with GaN VCSELs from UCSB has been their ina

8-band k.p theory was applied to bulk GaN and InN. The optical transitionintensity was computed and results show > 80-90% degree of polarization inthe direction of compression. Polarization switching is observed when strainwas reversed from compressive to tensile. 6 band k.p theory was used tostudy InGaN quantum dot/GaN elliptical pyramid structures. The opticaltransition intensity was calculated for different elongations of the pyramid.Elongation of the pyramid gives rise to a small polarization in the directionof the pyramid elongation. The optical transition intensity was calculatedfor elongated quantum dots and was strongly in uencing the polarization inthe direction of the quantum dot elongation, with a degree of polarization of >90%.

Vertical-cavity surface-emitting lasers (VCSELs) have a long history of development in GaAs-based and InP-based systems, however III-nitride VCSELs research is still in its infancy. Yet, over the past several years we have made dramatic improvements in the lasing characteristics of these highly complex devices. Specifically, we have reduced the threshold current density from ~100 kA/cm2 to ~3 kA/cm2, while simultaneously increasing the output power from ~10 µW to ~550 µW. These developments have primarily come about by focusing on the aperture design and intracavity contact design for flip-chip dual dielectric DBR III-nitride VCSELs. We have carried out a number of studies developing an Al ion implanted aperture (IIA) and photoelectrochemically etched aperture (PECA), while simultaneously improving the quality of tin-doped indium oxide (ITO) intracavity contacts, and demonstrating the first III-nitride VCSEL with an n-GaN tunnel junction intracavity contact. Beyond these most notable research fronts, we have analyzed numerous other parameters, including epitaxial growth, flip-chip bonding, substrate removal, and more, bringing further improvement to III-nitride VCSEL performance and yield. This thesis aims to give a comprehensive discussion of the relevant underlying concepts for nonpolar VCSELs, while detailing our specific experimental advances. In Section 1, we give an overview of the applications of VCSELs generally, before describing some of the potential applications for III-nitride VCSELs. This is followed by a summary of the different material systems used to fabricate VCSELs, before going into detail on the basic design principles for developing III-nitride VCSELs. In Section 2, we outline the basic process and geometry for fabricating flip-chip nonpolar VCSELs with different aperture and intracavity contact designs. Finally, in Section 3 and 4, we delve into the experimental results achieved in the last several years, beginning with a discussion on the epi

The (Al,Ga,In)N materials system has impacted energy efficiency on the world-wide scale through its application to blue light-emitting diodes (LEDs), which were invented and developed in the 1990s. Since then, cost reductions and performance improvements have brought GaN-based LEDs into the mainstream, supplanting outdated lighting technology and improving energy efficiency.One of the main challenges that still limits commercial LEDs, however, is “efficiency droop,” which refers to the reduction in efficiency as the input current density (and with it, the carrier density) increases. This phenomenon especially plagues high power LEDs, which operate in the current density range of 100-1000 A/cm2.Few practical options exist to directly eliminate efficiency droop, however we investigated two complementary approaches to circumvent the phenomenon. The first “high power solution” would employ blue laser diodes as the engine of solid state white lighting in lieu of LEDs. When laser diodes reach the threshold current density for stimulated emission, the carrier density in the active region clamps, simultaneously clamping droop. The wall plug efficiency of the laser diodes can then continue to rise as input current density increases until another effect (usually thermal) overrides it. The second “low power solution” maintains the blue LED as the solid state lighting engine, but shifts the operation point to low current density (and low carrier density) where efficiency droop effects are negligible and other thermal and electrical constraints in the device design are alleviated, enabling designs for high wall-plug efficiency. Both approaches to circumventing efficiency droop are likely to find a home in diverse future technologies and applications for lighting and displays.The challenge to produce high performance blue laser diodes was approached from an m-plane epitaxy platform. m-Plane is a non-polar orientation of the wurtzite (Al,Ga,In)N, which is free from deleterious pol

Basal plane III-nitride laser diodes have been commercialized for wide ranging technologies, including pico projectors for solid state RGB displays, optical data storage and automotive headlights. Active research is focused in solid state lighting and visible light communications. Despite widespread commercialization, c-plane devices are affected by the inherent spontaneous and piezoelectric polarizations of the basal plane. These polarization effects are significantly reduced in semipolar planes of GaN, creating a vast design space for III-nitride optoelectronic devices. III-nitride semipolar laser design and performance are considerably affected by the material composition and growth conditions of the cladding layers. The bottom cladding design is limited by stress relaxation of ternary alloys while the top cladding is limited by the growth time and temperature of the p-type (Al,In,Ga)N layers. These design limitations have been independently addressed by using limited area epitaxy (LAE) to enable n-AlGaN bottom cladding layers and by using thin p-GaN and transparent conducting oxide (TCO) top cladding layers. In this work, we investigate a new laser design that simultaneously incorporates LAE-enabled n-AlGaN bottom cladding and thin p-GaN and TCO top cladding layers in ( III-nitride laser structures. We evaluate the performance of two different TCOs as the top cladding layer: indium-tin-oxide (ITO) and zinc oxide (ZnO). Thorough optical modeling of the LAE-TCO laser design will be discussed for various Al compositions in the LAE-enabled n-AlGaN bottom cladding and varying p-GaN thicknesses in the top cladding. The LAE-TCO laser design was first demonstrated using ITO as the top cladding layer, with pulsed lasing achieved at 446 nm with a threshold current density of 8.5 kA/cm2 and a threshold voltage of 8.4 V. Insights from the optical modeling in conjunction with improvements in the LAE-TCO laser fabrication process led to the demonstration of the LAE-TCO design

Basal plane III-nitride laser diodes have been commercialized for wide ranging technologies, including pico projectors for solid state RGB displays, optical data storage and automotive headlights. Active research is focused in solid state lighting and visible light communications. Despite widespread commercialization, c-plane devices are affected by the inherent spontaneous and piezoelectric polarizations of the basal plane. These polarization effects are significantly reduced in semipolar planes of GaN, creating a vast design space for III-nitride optoelectronic devices. III-nitride semipolar laser design and performance are considerably affected by the material composition and growth conditions of the cladding layers. The bottom cladding design is limited by stress relaxation of ternary alloys while the top cladding is limited by the growth time and temperature of the p-type (Al,In,Ga)N layers. These design limitations have been independently addressed by using limited area epitaxy (LAE) to enable n-AlGaN bottom cladding layers and by using thin p-GaN and transparent conducting oxide (TCO) top cladding layers. In this work, we investigate a new laser design that simultaneously incorporates LAE-enabled n-AlGaN bottom cladding and thin p-GaN and TCO top cladding layers in ( III-nitride laser structures. We evaluate the performance of two different TCOs as the top cladding layer: indium-tin-oxide (ITO) and zinc oxide (ZnO). Thorough optical modeling of the LAE-TCO laser design will be discussed for various Al compositions in the LAE-enabled n-AlGaN bottom cladding and varying p-GaN thicknesses in the top cladding. The LAE-TCO laser design was first demonstrated using ITO as the top cladding layer, with pulsed lasing achieved at 446 nm with a threshold current density of 8.5 kA/cm2 and a threshold voltage of 8.4 V. Insights from the optical modeling in conjunction with improvements in the LAE-TCO laser fabrication process led to the demonstration of the LAE-TCO design

Vertical-cavity surface-emitting lasers (VCSELs) have a long history of development in GaAs-based and InP-based systems, however III-nitride VCSELs research is still in its infancy. Yet, over the past several years we have made dramatic improvements in the lasing characteristics of these highly complex devices. Specifically, we have reduced the threshold current density from ~100 kA/cm2 to ~3 kA/cm2, while simultaneously increasing the output power from ~10 µW to ~550 µW. These developments have primarily come about by focusing on the aperture design and intracavity contact design for flip-chip dual dielectric DBR III-nitride VCSELs. We have carried out a number of studies developing an Al ion implanted aperture (IIA) and photoelectrochemically etched aperture (PECA), while simultaneously improving the quality of tin-doped indium oxide (ITO) intracavity contacts, and demonstrating the first III-nitride VCSEL with an n-GaN tunnel junction intracavity contact. Beyond these most notable research fronts, we have analyzed numerous other parameters, including epitaxial growth, flip-chip bonding, substrate removal, and more, bringing further improvement to III-nitride VCSEL performance and yield. This thesis aims to give a comprehensive discussion of the relevant underlying concepts for nonpolar VCSELs, while detailing our specific experimental advances. In Section 1, we give an overview of the applications of VCSELs generally, before describing some of the potential applications for III-nitride VCSELs. This is followed by a summary of the different material systems used to fabricate VCSELs, before going into detail on the basic design principles for developing III-nitride VCSELs. In Section 2, we outline the basic process and geometry for fabricating flip-chip nonpolar VCSELs with different aperture and intracavity contact designs. Finally, in Section 3 and 4, we delve into the experimental results achieved in the last several years, beginning with a discussion on the epi

The (Al,Ga,In)N materials system has impacted energy efficiency on the world-wide scale through its application to blue light-emitting diodes (LEDs), which were invented and developed in the 1990s. Since then, cost reductions and performance improvements have brought GaN-based LEDs into the mainstream, supplanting outdated lighting technology and improving energy efficiency.One of the main challenges that still limits commercial LEDs, however, is “efficiency droop,” which refers to the reduction in efficiency as the input current density (and with it, the carrier density) increases. This phenomenon especially plagues high power LEDs, which operate in the current density range of 100-1000 A/cm2.Few practical options exist to directly eliminate efficiency droop, however we investigated two complementary approaches to circumvent the phenomenon. The first “high power solution” would employ blue laser diodes as the engine of solid state white lighting in lieu of LEDs. When laser diodes reach the threshold current density for stimulated emission, the carrier density in the active region clamps, simultaneously clamping droop. The wall plug efficiency of the laser diodes can then continue to rise as input current density increases until another effect (usually thermal) overrides it. The second “low power solution” maintains the blue LED as the solid state lighting engine, but shifts the operation point to low current density (and low carrier density) where efficiency droop effects are negligible and other thermal and electrical constraints in the device design are alleviated, enabling designs for high wall-plug efficiency. Both approaches to circumventing efficiency droop are likely to find a home in diverse future technologies and applications for lighting and displays.The challenge to produce high performance blue laser diodes was approached from an m-plane epitaxy platform. m-Plane is a non-polar orientation of the wurtzite (Al,Ga,In)N, which is free from deleterious pol

The III-nitride semiconductors, including AlN, InN, GaN, and BN have been demonstrated as technologically exciting materials for a wide range of device applications. With band gaps that span the visible range, GaN, InN, and InGaN alloys are used for high efficiency light emitting diodes for general lighting, as well as laser diodes for optical storage. The wide gaps, large band offsets, and polarization fields in AlN, GaN, and AlGaN alloys are promising for high-frequency, high-power transistors with applications in power conversion and radio frequency amplifiers.Despite the plethora of attractive material parameters of the III-nitride materials there are several issues that significantly limit the efficiency of devices and range of possible applications. In this study, we use first-principles electronic structure calculations to explore several of these properties relevant to understanding growth, processing, and device design.Arguably the most detrimental issue in this material system is the lack of widely available, cost-effective substrates for the growth of films and devices. Heteroepitaxy, as well as the lattice mismatch between the layers of different III-nitride alloys in heterostructures, results in residual stresses in films and devices. Such stress will alter the electronic structure of the materials, so it is necessary for device design to be able to quantify these effects. We explore the influence of strain on the effective mass of carriers in GaN and AlN, a parameter that is tied to the conductivity. In addition, films under tensile strain can crack if the strain energy is sufficient. We explore the propensity for AlN, GaN, and AlGaN to crack on different crystallographic planes.There has been significant work done to overcome the issue of residual strains in III-nitride films, both through the growth of bulk crystals for substrates, and the growth of structures such as nanowires that avoid many of the thickness and alloy-content limitations of epitaxi

Our era is defined by its technology, and our future is dependent on its continued evolution. Over the past few decades, we have witnessed the expansion of advanced technology into all walks of life and all industries, driven by the exponential increase in the speed and power of semiconductor-based devices.However, as the length scale of devices reaches the atomic scale, a deep understanding of atomistic theory and its application is increasingly crucial. In order to illustrate the power of an atomistic approach to understanding devices, we will present results and conclusions from three interlinked projects: n-type doping of III-nitride semiconductors, defects for quantum computing, and macroscopic simulations of devices.First, we will study effective n-type doping of III-nitride semiconductors and their alloys, and analyze the barriers to effective n-type doping of III-nitrides and their alloys. In particular, we will study the formation of DX centers, and predict alloy composition onsets for various III-nitride alloys. In addition, we will perform a comprehensive study of alternative dopants, and provide potential alternative dopants to improve n-type conductivity in AlN and wide-band-gap nitride alloys.Next, we will discuss how atomic-scale defects can act as a curse for the development of quantum computers by contributing to decoherence at an atomic scale, specifically investigating the effect of two-level state defects (TLS) systems in alumina as a source of decoherence in superconducting qubits based on Josephson junctions; and also as a blessing, by allowing the identification of wholly new qubits in different materials, specifically showing calculations on defects in SiC for quantum computing applications.Finally, we will provide examples of recent calculations we have performed for devices using macrosopic device simulations, largely in conjunction with first-principles calculations. Specifically, we will discuss the power of using a multi-scale approach t

The III-nitride semiconductors, including AlN, InN, GaN, and BN have been demonstrated as technologically exciting materials for a wide range of device applications. With band gaps that span the visible range, GaN, InN, and InGaN alloys are used for high efficiency light emitting diodes for general lighting, as well as laser diodes for optical storage. The wide gaps, large band offsets, and polarization fields in AlN, GaN, and AlGaN alloys are promising for high-frequency, high-power transistors with applications in power conversion and radio frequency amplifiers.Despite the plethora of attractive material parameters of the III-nitride materials there are several issues that significantly limit the efficiency of devices and range of possible applications. In this study, we use first-principles electronic structure calculations to explore several of these properties relevant to understanding growth, processing, and device design.Arguably the most detrimental issue in this material system is the lack of widely available, cost-effective substrates for the growth of films and devices. Heteroepitaxy, as well as the lattice mismatch between the layers of different III-nitride alloys in heterostructures, results in residual stresses in films and devices. Such stress will alter the electronic structure of the materials, so it is necessary for device design to be able to quantify these effects. We explore the influence of strain on the effective mass of carriers in GaN and AlN, a parameter that is tied to the conductivity. In addition, films under tensile strain can crack if the strain energy is sufficient. We explore the propensity for AlN, GaN, and AlGaN to crack on different crystallographic planes.There has been significant work done to overcome the issue of residual strains in III-nitride films, both through the growth of bulk crystals for substrates, and the growth of structures such as nanowires that avoid many of the thickness and alloy-content limitations of epitaxi

Our era is defined by its technology, and our future is dependent on its continued evolution. Over the past few decades, we have witnessed the expansion of advanced technology into all walks of life and all industries, driven by the exponential increase in the speed and power of semiconductor-based devices.However, as the length scale of devices reaches the atomic scale, a deep understanding of atomistic theory and its application is increasingly crucial. In order to illustrate the power of an atomistic approach to understanding devices, we will present results and conclusions from three interlinked projects: n-type doping of III-nitride semiconductors, defects for quantum computing, and macroscopic simulations of devices.First, we will study effective n-type doping of III-nitride semiconductors and their alloys, and analyze the barriers to effective n-type doping of III-nitrides and their alloys. In particular, we will study the formation of DX centers, and predict alloy composition onsets for various III-nitride alloys. In addition, we will perform a comprehensive study of alternative dopants, and provide potential alternative dopants to improve n-type conductivity in AlN and wide-band-gap nitride alloys.Next, we will discuss how atomic-scale defects can act as a curse for the development of quantum computers by contributing to decoherence at an atomic scale, specifically investigating the effect of two-level state defects (TLS) systems in alumina as a source of decoherence in superconducting qubits based on Josephson junctions; and also as a blessing, by allowing the identification of wholly new qubits in different materials, specifically showing calculations on defects in SiC for quantum computing applications.Finally, we will provide examples of recent calculations we have performed for devices using macrosopic device simulations, largely in conjunction with first-principles calculations. Specifically, we will discuss the power of using a multi-scale approach t

The investigators have undertaken several efforts underlying the enhancement of the performance of nanostructure-based quantum-dot-based optoelectronic devices. These include: the use of colloidal quantum dots as optoelectronic elements; investigating novel nanostructures (including graphene and CNTs as contacts) as components of quantum-dot based optoelectronic devices; investigating confined phonon effects in novel components of the integrated nanostructure-based optoelectronic structures; investigating energy transfer between quantum dot and PS-I; and the investigation of photodetector structures from these nanostructures and conducting polymers. Specific achievements include: first measurement of FRET times between PS-I and semiconductor quantum dots; measurement of large NDR in organic-inorganic optoelectronic structures; measurement of confined phonons in quantum dots; and design of novel three-color organic-inorganic photodetectors.

For more than fifteen years, III-nitrides have become the materials of choice for the realization of optoelectronics devices operating in the visible-UV spectral range. Yet, while nitride-based technology has truly exploded, the structural quality of this material-class is still low, which is a key issue regarding the radiative efficiency of light-emitting devices. A lot of work is thus devoted to improve the crystal quality of GaN and related materials. As current developments, we mention the reduction of threading dislocations, or the growth of III-nitrides heterostructures along non-polar crystal orientation. In parallel to the efforts dedicated to improve the quality of nitride-based epilayers, it is mandatory to grasp the mechanisms ruling the light-matter interaction, and, in particular, to detail the impact of defects on the radiative efficiency of optoelectronic devices. As a part of this research, the present thesis work is dedicated to the understanding of exciton relaxation and recombination phenomena in nitride-based nanostructures. This experimental study is carried out by time-resolved photo- and cathodoluminescence. We first focus on the emission properties of GaN nanocolumns, nanostructures that raise currently a huge interest, as they are free of any extended defect. Still, contrasting with their perfect structural quality, the low-temperature photoluminescence spectra of these nano-objects exhibit broad excitonic emission lines. In addition, one observes an intense emission line centered at 3.45 eV, a line absent from the luminescence spectra of high-quality GaN thick layers. We first demonstrate that these two features arise from the statistical distribution of donor atoms across the nanocolum: when a donor nucleus is located in the vicinity of the surface, its wave function is perturbed and the emission properties of donor bound excitons is profoundly altered. Based on a qualitative model, we estimate to 8 nm the thickness of the surface shell la

Ill-Nitride based optoelectronics support a variety of promising applications due to their tunable direct bandgap extending from deep ultraviolet towards green. We started by studying blue and green light emitting diode (LED) structures based on InGaN/GaN multiquantum wells (MQWs), grown on regular and lateral epitaxial overgrowth (LEO) GaN templates. We apply a unique pulsed epitaxy approach to achieve green LEDs. We also studied InGaN quantum dots for improved emission in the green spectrum. A novel hybrid green light-emitting diodes (LEDs) comprised of w-ZnO/ (InGaN/GaN) multi-quantum-wells/p-GaN were developed. The low temperature pulsed laser deposition (PLD) of the ZnO avoids the degradation typical when capping structures via metalorganic chemical vapor deposition. The results indicate that hybrid LED structures hold the prospects for developmenting green LEDs with superior performance. We also report on the current-voltage characteristic under forward biases obtained in low leakage, small size p-(In,Ga)N/GaN-n multiquantum well diodes. The detection of very low photon fluxes was reported under gated biasing in the 1 MV/cm range. We also reported on the fabrication and current-voltage characteristics of nanostructured p-i-n photodiodes based on GaN. Strong rectifying behavior was obtained; In contrast to GaN bulk p-i-n diodes, devices reproducibly show ideality factors lower than 2., The original document contains color images. All DTIC reproductions will be in black and white.

III-Nitrides, due to their large conduction band offset and fast transition speeds, are promising constituents for intersubband (ISB) devices. In addition, III-Nitrides are characterized by a very large phonon energy (90 meV). This makes them ideally suited to the realization of near room temperature operating THz lasers. The objective of this program has been to demonstrate the potential for using III-Nitrides to realize a room temperature operating terahertz intersubband laser., The original document contains color images.

AlGaN alloys with high Al contents, covering from 350 nm to 200 nm, are ideal materials for the development of efficient ultraviolet (UV) light sources/sensors. There are many problems and questions that still stand in the way of the practical device implementation of UV photonic devices. Among these, the attainment of highly conductive Al-rich AlGaN remains one of the biggest obstacles for the III-nitride research. The objectives of this program were to address some of the fundamental material and device issues and to explore potential applications of III-nitrides for UV micro- and nano-photonic devices. The KSU team has achieved 1. n-type Al-rich AlGaN alloys with record high conductivities. 2. converted highly insulating AlN to n-type conductive AlN by Si doping. 3. nano-fabrication and characterization of III-nitride photonic crystals (PC) and demonstrated the first current-injected III-nitride PC emitter operating below 330 nm. 4. p-type conduction in Al-rich AlxGa1-xN for x up to 0.7. 5. nano-fabrication of deep UV photonic crystals on AlN wafers. 6. achieved 280 nm UV LEDs that are among the best in the world. 7. demonstrated the operation of 200 nm DUV Schottky detectors based on AlN having a detectivity that is comparable to those of photomultiplier tubes., The original document contains color images.

High temperature annealing in air has been applied as an effective ex-situ surface treatment for the alpha-Al2O3(0001) substrates used in molecular beam epitaxy (MBE) growth of III-nitrides. The method is based on the criterion that atomically smooth surface of terrace-and-step like structure, which is considered to be crucial in obtaining a high quality epilayer, could be produced upon high temperature annealing. The annealed surface was mostly studied by atomic force microscopy (AFM) imaging. In this work, the effects of high temperature annealing on the surface morphology, crystalline quality, optical quality and surface reconstruction behaviour of alpha-Al2O3(0001) substrates were fully studied using AFM, triple-axis high resolution X-ray diffraction (THRXRD), spectroscopic ellipsometry (SE) and insitu reflection high-energy electron diffraction (RHEED). A new strategy, H-2 thermal cleaning at 1100 degrees C followed by O-2 annealing at 1300 degrees C was proposed as an efficient surface treatment for alpha-Al2O3 (0001) substrates for MBE growth., QC 20101006

There is a need for single photon detectors for a variety of scientific, military, and civilian applications. Compared to photomultiplier tubes or superconducting single photon detectors, the use of Geiger-mode avalanche photodiodes (APDs) presents advantages such as lower operation voltages, reduced sizes, and reduced need for cooling, which may enable the fabrication of more compact, lower power, and all-solid-state APD/CMOS integrated arrays. APDs based on wide-band-gap semiconductors are of special interest when there is a need for reliable ultraviolet detection with single photon counting capabilities. The tunable response of AlGaN detectors allows for solar- to visible-blind performances within the same material system, without the need of filters. We report on the growth, fabrication, and characterization of back-illuminated GaN APDs on thick AlN templates. Comparison of the performance of these same devices under front and back illumination allows us to reach a better understanding of carrier multiplication in this material and to determine experimentally both electron and hole ionization coefficients. Devices of various mesa sizes were fabricated and the effects of increased area on device performance were studied. Finally, devices were characterized in Geiger mode to evaluate their capabilities for single-photon detection., The original document contains color images.

Wide-gap III-Nitride based white light emission had been proven to yield luminescence efficiency (20-30 Lumen/W) and the III-Nitride devices proved long lifetime (>10khr). It is expected that high efficiency III-Nitride based white light emission will be the major lighting source for daily illumination in the coming decades. In 1998, the world energy consumption of energy is 69,000 TWh. There had been 2300 TWh consumption in illumination with rather inefficiently way. To further largely improve the luminescence efficiency beyond 100 Lumen/W and to increase thermal stability of the III-Nitride based LED, devices in the quantum structure is the viable way to pursuit.

We present calculations of the band structure, density of states and the real and imaginary parts of the dielectric functions in intrinsic TIN and AlN, both for wurtzite and the zinc-blende polytypes. They are based on the local density approximation (LDA) within the density functional theory (DFT), employing the first-principles, full-potential linearized augmented plane wave (FPLAPW) method. We correct the band gap of the AlN by using a quasi-particle method proposed by Bechstedt and Del Sole. The calculated energy gaps, lattice constants and dielectric constants for AlN are in good agreement with available experimental values while for TIN there is no experimental investigation., QC 20100525 QC 20111011

We report on the complex nature of infrared luminescence and absorption in InN films, which cannot be entirely explained by the concept of a conventional narrow-gap semiconductor. In particular, it concerns the detection of peaks near absorption edges by both thermally detected optical absorption and photoluminescence excitation spectroscopy and the observation of extraordinarily strong resonant enhancement of emission. To describe the experimental data a model is proposed, which takes into account surface plasmons in metal-like inclusions, modifying the optical properties of InN. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA,.

We report on low temperature photoluminescence (PL) in In xGa1-xN multiple quantum wells (MQWs) with x in the range 0.1 and highly Si doped barriers of In0.01Ga0.99N. One sample with 3 QWs of width 3.5 nm and barriers of width 10.5 nm had the MQW in the depletion region of the outer surface. Two PL peaks were observed, one QW exciton from the QW closest to the GaN buffer, one lower energy peak related to a 2DEG at the interface to the GaN buffer layer. In a second similar sample 5 QWs of width 3 nm and with 6 nm highly Si doped In0.01Ga 0.99N barriers the MQW was placed in the n-side depletion region of a pn-junction. At low temperatures the PL and electroluminescence (EL) spectra are quite different at no, low, or reverse bias, the PL appearing at higher energy. At high forward bias a spectral component at the EL position appears. This proves a strong influence of the depletion field on the optical spectra. Preliminary results are also reported for n-doped Al0.07Ga 0.93N/GaN structures, with near surface MQWs.

We present a full band calculation of the doping-induced energy shifts of the conduction-band minimum and the valence-band maximum for n- and p-type GaN and AlN. Both wurtzite and zinc-blende structures have been considered. The resulting optical and reduced band-gap energies are presented as functions of the ionized impurity concentration in the heavily doped regime. The computational method is based on a zero-temperature Green's function formalism within the random phase approximation and with the local-field correction of Hubbard. The calculation goes beyond the spherical approximation of the energy bands by using energy dispersions and overlap integrals from a first-principle, full-potential band-structure calculation. Inclusion of the spin-orbit interaction is crucial for describing the uppermost valence bands properly, and we show that the nonparabolicity of the valence bands influences the energy shifts strongly, especially the shift of the optical band gap. With the full band structure, we can explain the results of photoluminescence measurements by Yoshikawa [J. Appl. Phys. 86, 4400 (1999)]., QC 20100525