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Homoepitaxial growth of β-Ga2O3 on β-Ga2O3 substrates by halide vapor-phase epitaxy (HVPE) using GaCl and O2 was investigated by both thermodynamic analysis and growth experiments. The thermodynamic analysis clarified that growth of Ga2O3 is expected at high temperatures around 1000 °C using an inert carrier gas. The experimental results revealed that homoepitaxial growth of unintentionally doped (UID) layers with a low effective donor concentration (Nd − Na) of less than 1013 cm−3 is possible at 1000 °C on β-Ga2O3 (001) substrates with a high growth rate of up to 28 μm/h. Furthermore, HVPE growth of intentionally Si-doped β-Ga2O3 layers was investigated by supplying SiCl4, which revealed that n-type carrier density almost equal to the Si-doping concentration can be controlled in the range of 1015–1018 cm−3. The carrier mobility decreased with increasing Si impurity concentration and was about 150 cm2/V·s at room temperature for a layer with a carrier density of 3.2 × 1015 cm−3. Thus, the intentionally Si-doped homoepitaxial layers grown on β-Ga2O3 substrates can be applicable for the production of β-Ga2O3-based power devices.

Homoepitaxial growth of β-Ga2O3 layers by halide vapor phase epitaxy (HVPE) using O2 or H2O as an oxygen source was investigated by thermodynamic analysis, and compared with measured properties after growth. The thermodynamic analysis revealed that Ga2O3 growth is expected even at 1000 °C using both oxygen sources due to positive driving forces for Ga2O3 deposition. The experimental results for homoepitaxial growth on (0 0 1) β-Ga2O3 substrates showed that the surfaces of the layers grown with H2O were smoother than those grown with O2, although the growth rate with H2O was approximately half that with O2. However, in the homoepitaxial layer grown using H2O, incorporation of Si impurities with a concentration almost equal to the effective donor concentration (2 × 1016 cm−3) was confirmed, which was caused by decomposition of the quartz glass reactor due to the presence of hydrogen in the system.

The effect of the growth conditions on halide vapor phase epitaxy of In2O3 on sapphire (0 0 0 1) substrates was investigated. Only the most thermally stable phase c-In2O3 grows at growth temperatures of 400 to 1000 °C. The growth rate increased as the growth temperature increased up to 700 °C, and layers with rough surfaces and a preferred (1 0 0) orientation were grown. Above 700 °C, the growth rate became constant, the preferential orientation changed to (1 1 1), and layers with smooth surfaces were grown. At 1000 °C, the volume fraction of the (1 1 1)-oriented domains in the grown layer reached 99.0%, although there were in-plane twins rotated by 180°. The growth rate also increased as the input partial pressure of the InCl or O2 source gas was increased, and a high growth rate exceeding 10 μm/h was found. The layer grown at 1000 °C was of high purity and incorporated no impurities other than Cl. Optical transmission measurements of this layer showed high optical transmittance at energies below the optical gap of 3.47 eV.

The growth of thick InGaN layers on free-standing GaN (0001¯) substrates was studied using tri-halide vapor phase epitaxy. It was found that high-indium-content InGaN can be grown under higher InCl 3 input partial pressure at higher growth temperature, which allows the fabrication of a high crystalline quality InGaN layer with a smooth surface morphology. Using the growth conditions of high InCl 3 input partial pressure and high growth temperature, crack- and droplet-free InGaN layers with a thickness of over 10 µm and with an indium fraction of 0.05 were successfully grown. Although the surface showed many hillocks, the number of hillocks was reduced upon growth of thicker InGaN layers. Photoluminescence measurements confirm that thick InGaN layers could be successfully grown without degradation of the crystalline quality.

Silicon doped homoepitaxial films were grown on beta‑gallium oxide (001) substrates by halide vapor phase epitaxy using gallium monochloride, oxygen and silicon tetrachloride gases as precursors. It was confirmed that the n-type carrier density at room temperature was almost equal to the doped silicon concentration, which was controlled in the range of 1015 to 1018 cm−3. In the doped film with the carrier density of 1 × 1016 cm−3, the activation energy and the mobility at room temperature were 45.6 meV and 145 cm2/V⋅s, respectively. The carrier scattering mechanism in the low carrier density film was dominated by optical phonon scattering with the phonon energy of 33 meV. These results suggest that the doped homoepitaxial film grown by halide vapor phase epitaxy is a high quality film with good crystallinity comparable to bulk crystals.

In this work, we present a method to synthesize arrays of hexagonal InGaN submicrometer platelets with a top c-plane area having an extension of a few hundred nanometers by selective area metal-organic vapor-phase epitaxy. The InGaN platelets were made by in situ annealing of InGaN pyramids, whereby InGaN from the pyramid apex was thermally etched away, leaving a c-plane surface, while the inclined {1011} planes of the pyramids were intact. The as-formed c-planes, which are rough with islands of a few tens of nanometers, can be flattened with InGaN regrowth, showing single bilayer steps and high-quality optical properties (full width at half-maximum of photoluminescence at room temperature: 107 meV for In0.09Ga0.91N and 151 meV for In0.18Ga0.82N). Such platelets offer surfaces having relaxed lattice constants, thus enabling shifting the quantum well emission from blue (as when grown on GaN) to green and red. For single InGaN quantum wells grown on the c-plane of such InGaN platelets, a sharp interface between the quantum well and the barriers was observed. The emission energy from the quantum well, grown under the same conditions, was shifted from 2.17 eV on In0.09Ga0.91N platelets to 1.95 eV on In0.18Ga0.82N platelets as a result of a thicker quantum well and a reduced indium pulling effect on In0.18Ga0.82N platelets. On the basis of this method, prototype light-emitting diodes were demonstrated with green emission on In0.09Ga0.91N platelets and red emission on In0.18Ga0.82N platelets.

Deep-level luminescence at 3.3 eV related to the presence of Al vacancies (V Al ) was observed in room temperature photoluminescence (RT-PL) spectra of homoepitaxial AlN layers grown at 1450 °C by hydride vapor-phase epitaxy (HVPE) and cooled to RT in a mixture of H 2 and N 2 with added NH 3 . However, this luminescence disappeared after removing the near surface layer of AlN by polishing. In addition, the deep-level luminescence was not observed when the post-growth cooling of AlN was conducted without NH 3 . Secondary ion mass spectrometry (SIMS) studies revealed that although the point defect density of the interior of the AlN layers remained low, the near surface layer cooled in the presence of NH 3 was contaminated by Si impurities due to both suppression of the surface decomposition by the added NH 3 and volatilization of Si by decomposition of the quartz reactor walls at high temperatures. The deep-level luminescence reappeared after the polished AlN wafers were heated in presence of NH 3 at temperatures above 1400 °C. The surface contamination by Si is thought to generate V Al near the surface by lowering their formation energy due to the Fermi level effect, resulting in deep-level luminescence at 3.3 eV caused by the shallow donor (Si) to V Al transition.

We report on photoluminescence (PL) spectroscopy and electron microscopy studies of an AlGaN quantum well (QW) structure grown by molecular beam epitaxy under metal-rich conditions with substrate rotation. Both techniques reveal unintentional formation within the AlGaN barriers of a quasiperiodic structure of thin Ga-rich layers, whose period is controlled by both the substrate rotation rate and the AlGaN growth rate. These compositional modulations act as 1-3 monolayer thick QWs emitting below 250 nm with an internal quantum efficiency (IQE) as high as ∼30% at room temperature under weak excitation. Variational calculations of the QW exciton properties indicate that the observed high IQE can result from strong three-dimensional localization of the excitons confined in the narrow QWs. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Growth of Si-doped AlN layers by hydride vapor phase epitaxy on AlN/sapphire templates prepared by metalorganic vapor phase epitaxy and bulk AlN substrates prepared by physical vapor transport was investigated using silicon tetrachloride (SiCl4) as a doping gas. On the AlN/sapphire templates, when the SiCl4 supply was low, the incorporation ratio of Si decreased due to the influence of O impurities resulting from the decomposition of the sapphire. In addition, pits were formed on the surfaces, and the pit density increased significantly at Si concentrations exceeding 2 × 1019 cm-3. In contrast, on the bulk AlN substrates, the Si concentration increased linearly with increasing SiCl4 supply, and a pit- and stress-free layer could be grown with a Si concentration as high as 6.5 × 1019 cm-3. Hall effect measurements revealed that this layer exhibited n-type conductivity with a donor activation energy of 253 meV. However, the carrier density at room temperature (RT) was as low as 3.6 × 1013 cm-3 because of the high compensation ratio due to the presence of acceptors. A broad peak centered at 3.3 eV was observed in the RT photoluminescence spectra of the Si-doped AlN layers grown on the bulk AlN substrates, indicating that Al vacancies formed by the Fermi level effect due to Si doping acted as acceptors that compensated for carriers.

Unintentionally doped n-type beta -Ga2O3 becomes highly resistive after annealing at high temperatures in oxygen ambient. The annealing process also induces an electron paramagnetic resonance (EPR) center, labeled IR1, with an electron spin of S=1/2 and principal g-values of g(xx)=2.0160, g(yy)=2.0386, and g(zz)=2.0029 with the principal axis of g(zz) being 60 degrees from the [001](*) direction and g(yy) along the b-axis. A hyperfine (hf) structure due to the hf interaction between the electron spin and nuclear spins of two equivalent Ga atoms with a hf splitting of similar to 29G (for Ga-69) has been observed. The center can also be created by electron irradiation. Comparing the Ga hf constants determined by EPR with corresponding values calculated for different Ga vacancy-related defects, the IR1 defect is assigned to the double negative charge state of either the isolated Ga vacancy at the tetrahedral site (V-Ga(I)(2-)) or the V-Ga(I)-Ga-ib-V-Ga(I) complex. Funding Agencies|DFGGerman Research Foundation (DFG) [FR2833/63-1]; HLRN [hbc00027]; Institute of Global Innovation Research, Tokyo; University of Agriculture and Technology, Japan

We developed a coherent Raman microspectroscopy that realizes a three-dimensional visualization of the spatial distribution of optical phonon modes in wide-bandgap semiconductors. This microspectroscopy will be a powerful tool for measuring the carrier concentration in semiconductors.

Point defects in semiconductors play a fundamental role for the material properties. Dopants like impurities forming shallow donors and acceptors provide the means of controlling the electrical conductivity of the material, which is the basis of many applications in devices. Native defects like vacancies and interstitial atoms, and their combination with impurities introduce, mostly unwanted deep levels in the bandgap, and thus may serve as traps or recombination centers for the carriers. Some of these defects are introduced during the growth of the material, others by the processing steps necessary in the device production. In this chapter, we present current knowledge about point defects in the III-nitrides based on recent works, both experimental and theoretical, in the field. Materials discussed are AlN, GaN and InN and the ternary alloys between them.

We employ an eigenpolarization model including the description of direction dependent excitonic effects for rendering critical point structures within the dielectric function tensor of monoclinic b ...

The isotropic average conduction band minimum electron effective mass in Sn-doped monoclinic single crystal beta-Ga2O3 is experimentally determined by the mid-infrared optical Hall effect to be (0.2846 +/- 0.013)m(0) combining investigations on (010) and ((2) over bar 01) surface cuts. This result falls within the broad range of values predicted by theoretical calculations for undoped beta-Ga2O3. The result is also comparable to recent density functional calculations using the Gaussian-attenuation-Perdew-Burke-Ernzerhof hybrid density functional, which predict an average effective mass of 0.267m(0). Within our uncertainty limits, we detect no anisotropy for the electron effective mass, which is consistent with most previous theoretical calculations. We discuss upper limits for possible anisotropy of the electron effective mass parameter from our experimental uncertainty limits, and we compare our findings with recent theoretical results. Published by AIP Publishing. Funding Agencies|Swedish Research Council (VR) [2013-5580, 2016-00889]; Swedish Governmental Agency for Innovation Systems (VINNOVA) under the VINNMER international qualification program [2011-03486]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University, Faculty Grant SFO Mat LiU [2009 00971]; Swedish Foundation for Strategic Research (SSF) [FL12-0181, RIF14-055]; University of Nebraska-Lincoln; J. A. Woollam Co., Inc.; J. A. Woollam Foundation; National Science Foundation [MRSEC DMR 1420645, CMMI 1337856, EAR 1521428]

The optical properties of the group-III-nitride materials are obviously of direct relevance for optoelectronic applications, but experiments measuring optical properties also give information on a range of electronic properties. There is already a wealth of data in the literature on the optical properties of III-nitrides [1-4], and here we will concentrate on some of the most recent additions to the scientific knowledge. The focus, looking at the present situation concerning technical applications of these materials, has been on GaN, InGaN, and AlGaN in recent decades. AlGaN materials are important for ultraviolet (UV) emitters and high electron mobility transistor (HEMT) structures and AlGaN optical properties have accordingly been studied over the entire Al composition range. InGaN materials (with In content

In this work, growth of InN quantum dots (QDs) on GaN nanowires (NWs) by metal-organic vapour phase epitaxy is demonstrated, illustrating the feasibility to combine 0D and 1D structures for nitride semiconductors. Selective area growth was used to generate arrays of c-oriented GaN NWs using Si3N4 as the mask material. In general, InN QDs tend to form at the NW edges between the m-plane side facets, but the QD growth can also be tuned to the side facets by controlling the growth temperature and the growth rate. TEM characterization reveals that I1-type stacking faults are formed in the QDs and originate from the misfit dislocations at the InN/GaN interface. Photoluminescence measurement at 4 K shows that the peak shifts to high energy with reduced dot size. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The thermal stability of +/- c- and m-plane GaN substrates and its dependence on the m-plane GaN off-cut angle were investigated at and above 1200 degrees C at atmospheric pressure in flowing N-2 w ...

We succeeded in fabricating HVPE-grown Ga2O3 FP-SBDs with a record Vbr/sub> of over 1 kV. This is an important step in the research and development of Ga2O3 power devices toward practical applications and future commercialization. This work was partially supported by Council for Science, Technology, and Innovation (CSTI), Cross-ministerial Strategic Innovation Promotion Program (SIP), "Next-generation power electronics" (funding agency: NEDO).

Photoluminescence spectroscopy is an important approach for examining the optical interactions in semiconductors and optical devices with the goal of gaining insight into material properties. With contributions from researchers at the forefront of this field, Handbook of Luminescent Semiconductor Materials explores the use of this technique to study semiconductor materials in a variety of applications, including solid-state lighting, solar energy conversion, optical devices, and biological imaging.After introducing basic semiconductor theory and photoluminescence principles, the book focuses on the optical properties of wide-bandgap semiconductors, such as AlN, GaN, and ZnO. It then presents research on narrow-bandgap semiconductors and solid-state lighting. The book also covers the optical properties of semiconductors in the nanoscale regime, including quantum dots and nanocrystals.This handbook explains how photoluminescence spectroscopy is a powerful and practical analytical tool for revealing the fundamentals of light interaction and, thus, the optical properties of semiconductors. The book shows how luminescent semiconductors are used in lasers, photodiodes, infrared detectors, light-emitting diodes, solid-state lamps, solar energy, and biological imaging.Show more Show less

We derive a dielectric function tensor model approach to render the optical response of monoclinic and triclinic symmetry materials with multiple uncoupled infrared and farinfrared active modes. We apply our model approach to monoclinic $\beta$-Ga$_2$O$_3$ single crystal samples. Surfaces cut under different angles from a bulk crystal, (010) and ($\bar{2}$01), are investigated by generalized spectroscopic ellipsometry within infrared and farinfrared spectral regions. We determine the frequency dependence of 4 independent $\beta$-Ga$_2$O$_3$ Cartesian dielectric function tensor elements by matching large sets of experimental data using a point by point data inversion approach. From matching our monoclinic model to the obtained 4 dielectric function tensor components, we determine all infared and farinfrared active transverse optic phonon modes with $A_u$ and $B_u$ symmetry, and their eigenvectors within the monoclinic lattice. We find excellent agreement between our model results and results of density functional theory calculations. We derive and discuss the frequencies of longitudinal optical phonons in $\beta$-Ga$_2$O$_3$. We derive and report density and anisotropic mobility parameters of the free charge carriers within the tin doped crystals. We discuss the occurrence of longitudinal phonon plasmon coupled modes in $\beta$-Ga$_2$O$_3$ and provide their frequencies and eigenvectors. We also discuss and present monoclinic dielectric constants for static electric fields and frequencies above the reststrahlen range, and we provide a generalization of the Lyddane-Sachs-Teller relation for monoclinic lattices with infrared and farinfrared active modes. We find that the generalized Lyddane-Sachs-Teller relation is fulfilled excellently for $\beta$-Ga$_2$O$_3$., Comment: 18 pages, 12 figures, 105 references; Presented at IWGO 2015 Nov. 4th, Kyoto, Japan

Electron paramagnetic resonance was used to study the donor that is responsible for the n-type conductivity in unintentionally doped (UID) beta-Ga2O3 substrates. We show that in as-grown materials, the donor requires high tempeature annealing to be activated. In partly activated materials with the donor concentration in the 10(16) cm(-3) range or lower, the donor is found to behave as a negative-U center (often called a DX center) with the negative charge state DX- lying similar to 16-20 meV below the neutral charge state d(0) (or E-d), which is estimated to be similar to 28-29 meV below the conduction band minimum. This corresponds to a donor activation energy of E-a similar to 44-49 meV. In fully activated materials with the donor spin density close to similar to 1 x 10(18) cm(-3), donor electrons become delocalized, leading to the formation of impurity bands, which reduces the donor activation energy to E-a similar to 15-17 meV. The results clarify the electronic structure of the dominant donor in UID beta-Ga2O3 and explain the large variation in the previously reported donor activation energy. Published by AIP Publishing. Funding Agencies|Linkoping Linnaeus Initiative for Novel Functional Materials (LiLi-NFM); Council for Science, Technology and Innovation (CSTI); Cross-ministerial Strategic Innovation Promotion Program (SIP); NEDO, Japan

So far, the semiconductor nanowire research area has mainly delivered results on growth procedures and related material properties. As the development lately has been successful in producing novel nanowire-based structures for optical or electronic applications, the time is ripe to review the device work that has been done and in some cases has produced devices ready for the market. In this chapter, we shall review the specific area of nanowire-based LEDs (NW-LEDs) for visible light, including the application area of “solid state lighting” (SSL). A brief review of the progress in the area of visible light LEDs over the last half century is presented, this also mentions some of the progress made in the planar technology so far. The most successful way of producing white light is still based on the use of phosphors, just like in the present compact fluorescence lamps (CFLs). The reason for this is the high efficiency (external quantum efficiency > 80%) possible at low currents in the violet planar InGaN-based LEDs used to excite the phosphors. These LEDs are presently mainly produced on foreign substrates, leading to a high dislocation density (DD) and a sizeable droop at high injection currents (25–40%). This droop and the down conversion energy loss in the phosphors (20–25%) has motivated the interest for a phosphor-less white light source based on direct mixing of light of different wavelength (such as red, green, and blue; RGB). To be competitive, this solution must be based on highly efficient LEDs for all RGB (red, green, and blue) colors. Since NW-LED structures can be produced basically free of structural defects (even if grown on a foreign substrate), the idea of using the RGB mixing concept for the production of white light sources with an ultimately higher efficiency than for the phosphor-based lamps is a major technical target for a second generation of light sources in the SSL field. Basic concepts behind the design and optical properties of NW-LED structures are discussed in this chapter, with emphasis on the present developments of III-nitride-based structures. The growth procedure relevant for such NW-LED structures is reported in some detail, specifically the core–shell configuration readily produced with metalorganic vapor phase epitaxy (MOVPE). The first generation processing technology for NW-LED structures is briefly described; this is naturally quite different from the established routines for planar LED chips. Experimental data for nitride-based NW-LEDs for blue, green, and even longer wavelengths are given in terms of radiative efficiencies, light outcoupling, droop, and long-term reliability. The experience so far is that for these NW-based emitters, efficiencies can be obtained that are close to those for the corresponding planar LEDs. There are still problems with the reproducibility of the radiative output, as well as a significant droop that would not be expected for m -plane emitters. More work is needed to pinpoint the cause of these problems. Finally, we briefly discuss various applications (also other than white lamps) where the NW-LEDs may have a specific advantage.

In this work we study the optical properties of two high quality fifty-periods of In-polarity InN/In0.73Ga0.27N MQWs samples, grown by radio-frequency plasma-assisted molecular beam epitaxy, with different well (0.5-1 nm) and barrier thicknesses (3-4 nm). We employ spectroscopic ellipsometry at room temperature in the energy range from 0.6 to 6 eV, and incidence angles of 60 and 70°. Ellipsometric data were successfully modelled using the model dielectric function approach and a multilayer model assuming the MQWs as a homogeneous layer. The E0, A and E1 MQWs transition energies were determined and found to exhibit a blueshift with decreasing the well thickness.

We report on optical studies of exciton localization and recombination kinetics in two single 2.2 nm thick AlxGa1-xN/Alx+0.1Ga0.9-xN quantum well structures (x = 0.55 and 0.6) grown by plasma assisted molecular beam epitaxy on a c-sapphire substrate. Strong localization potential inherent for both the quantum well and barrier regions results in merging of the quantum well and barrier emission spectra into a single broad line centered at 285 nm (x = 0.55) and 275 nm (x = 0.6). Time-resolved photoluminescence measurements revealed surprising temperature stability of the photoluminescence decay time constant (approximate to 400 ps) relevant to the recombination of the quantum well localized excitons. This observation implies nearly constant quantum efficiency of the quantum well emission in the whole range from 4.6 to 300 K.

GaN substrates with low dislocation densities were prepared by halide vapor-phase epitaxy (HVPE) on c-plane sapphire and by means of a post-growth laser-induced lift-off or natural stress-induced (self-) separation process. The HVPE growth on InGaN/GaN buffer layers and subsequent self-separation method was seen as advantageous, in comparison with the laser-induced lift-off one, in terms of lower cost and better crystalline quality of the GaN material obtained. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

New electron paramagnetic resonance (EPR) measurements in hexagonal and cubic GaN intentionally doped with silicon are presented. In both type of samples the well-known EPR resonance of the dominant shallow donor is observed, whereby the g-tensors are determined to g(parallel to) = 1.9512, g(perpendicular to) = 1.9485 (free-standing hexagonal GaN) and g = 1.9533 (cubic GaN layer grown on 3C-SiC substrate). The spectra show an exceptionally small line width below 0.4 mT and contain no further signature. As a result, beside the line width itself, the EPR line is characterized by its g-tensor exclusively. With the help of a qualitative analysis of the Si donor wave function within effective mass theory (EMT) and a followed up calculation of the hyperfine (HF) splittings in the framework of density functional theory (DFT) the characteristic shape of the EPR lines can be explained by an enhanced delocalization of the unpaired electrons of shallow Si donors at the gallium sublattice due to overlapping impurity and conduction bands.

We have demonstrated optically pumped room-temperature pulse lasing at 300.4 nm from an AlGaN-based multiple-quantum-well (MQW) structure grown by plasma-assisted molecular beam epitaxy on a c-sapphire substrate. The lasing was achieved at the threshold peak power of similar to 12 MW/cm(2). The MQW structure involved AlGaN/AlN short-period super-lattices to decrease the threading dislocation densities from 10(11) down to 10(9)-10(10) cm(-2). Studies of time-resolved photoluminescence (TRPL) spectra and cw PL temperature dependences (10-300K) of different MQW structures, as well as numerical calculations of the optical gain and confinement in the laser structure allowed us to conclude about the optimum design of AlGaN-based MQW structures for the lower threshold UV lasing.

Uniform arrays of submicron hexagonal InGaN pyramids with high morphological and material homogeneity, reaching an indium composition of 20%, are presented in this work. The pyramids were grown by selective area metal-organic vapor phase epitaxy and nucleated from small openings in a SiN mask. The growth selectivity was accurately controlled with diffusion lengths of the gallium and indium species, more than 1 μm on the SiN surface. High material homogeneity of the pyramids was achieved by inserting a precisely formed GaN pyramidal seed prior to InGaN growth, leading to the growth of well-shaped InGaN pyramids delimited by six equivalent 10 1 ¯ 1 facets. Further analysis reveals a variation in the indium composition to be mediated by competing InGaN growth on two types of crystal planes, 10 1 ¯ 1 and (0001). Typically, the InGaN growth on 10 1 ¯ 1 planes is much slower than on the (0001) plane. The formation of the (0001) plane and the growth of InGaN on it were found to be dependent on the morphology of the GaN seeds. We propose growth of InGaN pyramids seeded by 10 1 ¯ 1-faceted GaN pyramids as a mean to avoid InGaN material grown on the otherwise formed (0001) plane, leading to a significant reduction of variations in the indium composition in the InGaN pyramids. The InGaN pyramids in this work can be used as a high-quality template for optoelectronic devices having indium-rich active layers, with a potential of reaching green, yellow, and red emissions for LEDs.

We have investigated the feasibility to use GaN lattice-matched Al0.82In0.18N as a starting layer for growth of thick GaN using halide vapor phase epitaxy (HVPE). The buffer, which consisted of Al0 ...

Defect related carrier recombination and transport properties have been investigated in differently doped HVPE GaN substrates and CVD diamond layers. Carrier generation by interband transitions or by deep-defect photoexcitation were realized for studies of GaN samples by using picosecond pulses at 351 nm or 527 nm. This allowed to create favorable conditions for radiative and nonradiative recombination in the crystals and reveal peculiarities of photoelectrical properties of high and low density plasma in undoped, doped, and compensated GaN. In CVD diamonds, carrier diffusion length was found equal to ~ 0.5 μm and non-dependent on nitrogen density, while the carrier lifetime varied from 0.2 to 0.6 ns.

We report on recent optical investigations of free and bound exciton properties in bulk GaN. In order to obtain reliable data it is important to use low defect density samples of low doping. We have used thick GaN layers (of the order of 1 mm) grown by halide vapour phase epitaxy (HVPE) with a residual doping down to

This chapter serves as an introduction to the chapters on III-nitrides in this book. It gives a brief review of the development of relevant III-nitride materials for light emitters since the late 1960´s, when single crystalline GaN layers grown on sapphire were first demonstrated. The first wave of scientific work died out in the late 1970´s, since low-ohmic p-GaN could not be made at the time. After another 10 years several important breakthroughs were made, using the technology of metal organic vapor phase epitaxy (MOVPE). Smooth thin epilayers could be made, and ways to dope the materials n-type as well as p-type were invented. In the period 1986-1997 high brightness violet and blue double heterostructure (DH) LEDs, narrow quantum well (QW) LEDs, and QW based violet laser diodes with a long operating lifetime of 10000 hours were demonstrated, mainly by Japanese groups. Since then the development efforts have spread worldwide, and a large spectrum of novel applications based on nitride emitters are already in practical use. Perhaps the most important one is the future possibility of using nitride LEDs for general lighting purposes.

We have studied composition and strain in Al1–xInxN films with 0.128≤ x≤ 0.22 grown on GaN-buffered sapphire substrates by metalorganic vapor phase epitaxy. A good agreement between the In contents determined by Rutherford backscattering spectrometry (RBS) and Xray diffraction (XRD) is found for x≤ 18, suggesting applicability of Vegard's rule in the narrow compositional range around the lattice matching to GaN. The increase of the In content up to x = 0.22 leads to a formation of sub-layers with a higher composition, accompanied by deviations from Vegard's rule. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Freestanding GaN layers of various thicknesses grown by HVPE have been studied by time-resolved spectroscopy combined with structural and electrical measurements. We have observed an increase of th ...

We report new data on the transient photoluminescence behaviour of free and donor bound excitons in high quality bulk GaN material grown by HVPE. With 266 nm photoexcitation the no-phonon free exci ...

In this work we are presenting growth results of thick gallium nitride (GaN), numerical modeling and optimization of a vertical hot-walled halide vapor-phase epitaxy reactor. Using a simulation mod ...

The lattice parameters of low-defect density undoped bulk GaN fabricated by halide vapor phase epitaxy (HVPE) and removal of the substrate are precisely determined using high-resolution X-ray diffraction. The obtained values, c = 5.18523 A ˚ and a = 3.18926 A ˚ are compared with the lattice parameters of free-standing HVPE-GaN from different sources and found to be representative for state-of-the-art undoped HVPE bulk GaN material. A comparison with bulk GaN fabricated by the high pressure technique and homoepitaxial GaN layer is made, and the observed differences are discussed in terms of their free-electron concentrations, point and structural defects.

Measurements of the optical Hall effect in naturally doped high-quality wurtzite-structure InN thin films by generalized ellipsometry reveal that both the surface and the interior (bulk) free electron densities decrease with powerlaw dependencies on the film thickness. We discover a significant deviation between the bulk electron and dislocation densities. This difference is attributed here to the existence of surface defects with activation mechanism different from bulk dislocations and identifies the possible origin of the so far persistent natural n-type conductivity in InN. We further quantify the anisotropy of the C-point effective mass.

We report on low-temperature microphotoluminescence (μ-PL) measurements of InAs/GaAs quantum dots (QDs) exposed to a lateral external electric field. It is demonstrated that the QDs’ PL signal could be increased severalfold by altering the external and/or the internal electric field, which could be changed by an additional infrared laser. A model which accounts for a substantially faster lateral transport of the photoexcited carriers achieved in an external electric field is employed to explain the observed effects. The results obtained suggest that the lateral electric fields play a major role for the dot luminescence intensity measured in our experiment—a finding which could be used to tailor the properties of QD-based optoelectronic applications.

Experimental and computation results based on chemical composition assessment of metal-organic chemical vapour deposition grown undoped GaN/AlxGa1-xN multiquantum well structures in the low composition limit of x = 0.07 and wide wells demonstrate composition fluctuations in the barrier layers which lead to large-scale nonuniformities and inequivalence of the different wells. As a consequence the experimental photoluminescence spectra at low temperature show a double peak structure indicative of well-width fluctuations by one lattice parameter (2 monolayers).

Nonpolar a- and m-plane bulk GaN sliced from boules : structural and optical characteristics