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Far‐ultraviolet‐C (far‐UVC) light emitting diodes (LED) emitting at an emission wavelength of 226 nm with different n‐AlGaN contact layers, quantum well barriers, and quantum well numbers are compared regarding their emission power, operation voltage, and lifetime. Electroluminescence measurements show higher emission power but also an increased operation voltage with increasing Al mole fraction in the n‐AlGaN contact layer. Furthermore, it is found that both the mean emission power and the device lifetime decrease with increasing Al mole fraction (82–89%) of the quantum well barriers and therefore with increasing barrier height. Finally, 226 nm LEDs with 6 and 9 quantum wells are compared. It is observed that the sample with 9 quantum wells shows an around 30% lower mean emission power but, in contrast, the L70 lifetime of these LEDs is higher by a factor of around five. Based on these optimizations, 226 nm LEDs with a maximum external quantum efficiency of 0.28% (wall plug efficiency of 0.18%) as well as an emission power of 2.1 mW and an operation voltage of 9.6 V at 200 mA are realized. [ABSTRACT FROM AUTHOR]

High-power, broad-area, semiconductor lasers are attractive sources for material processing, aerospace, and laser pumping. The design of the active region is crucial to achieve the required high power and electro-optical conversion efficiency, since the temperature significantly affects the performance of the quantum well, including the internal quantum efficiency and mode gain. In this work, the temperature effects on the active region of a 808 nm high-power semiconductor laser were investigated theoretically and experimentally. The simulations were performed with a Quasi-3D model, which involved complete steady-state semiconductor and carrier confinement efficiency combined with a new mathematical method. The critical aluminum content of the quantum barrier was proposed and the relationship between temperature and various loss sources was disclosed in the temperature range of 213 to 333 K, which provides a reliable reference for the design of epitaxial structures of high-power semiconductor lasers in different operating conditions. Subsequently, the optimized epitaxial structure was determined and used to fabricate standard laser bar chips with a cavity length of 2 mm. The experimental electro-optical conversion efficiency of 71% was demonstrated with a slope efficiency of 1.34 W/A and an injection current of 600 A at the heatsink temperature of 223 K. A record high electro-optical conversion efficiency of 73.5% was reached at the injection current of 400 A, while the carrier confinement efficiency was as high as 98%. [ABSTRACT FROM AUTHOR]

AlGaN based deep ultraviolet (DUV) light-emitting diodes (LEDs), especially with a wavelength below 250 nm, have great application potential in the fields of sterilization and disinfection, gas sensing, and other aspects. However, with the decrease of emission wavelength, performance collapse occurs and the external quantum efficiencies (EQE) of sub-250 nm LEDs are usually below 1% for a long time. Low efficiencies are resulted from problem accumulation of all aspects, including n/p-type doping and contacts, carrier confinements and transports, light extraction, etc. To achieve high EQE of sub-250 nm LEDs, problems and solutions need to be discussed. In this paper, the research progress, development bottlenecks, and corresponding solutions of sub-250 nm LEDs are summarized and discussed in detail. [ABSTRACT FROM AUTHOR]

Summary: Kesterite Cu2ZnSnS4(CZTS) thin‐film technology has been comprehensively investigated over the last decade as a promising candidate in the field of photovoltaic technologies. However, despite numerous strategies to improve the performance, the efficiencies remain stagnant at around 11%. Poorly optimized absorber/buffer interface, non‐absorption of higher wavelength photons, and non‐ohmic back contact are the primary reasons for the poor performance of the CZTS solar cell. The authors of this paper propose a cadmium‐free buffer layer, multiple quantum wells (MQWs) structure, and a back surface field (BSF) layer to overcome these issues, respectively. In this study, the buffer layer, zinc oxysulfide (Zn[O1−xSx]) is considered as an alternative to toxic Cadmium Sulfide (CdS) for better band alignment with the CZTS absorber layer. Cu2ZnSn(SxSe1−x)4 (CZTSSe) is used as a quantum well material in MQWs to increase photon absorption in CZTS solar cells. Tin selenide (SnSe) is used as the BSF layer to reduce the effect of non‐ohmic back contact and to improve the open‐circuit voltage (Voc) of MQW incorporated CZTS solar cells. Detailed analysis and optimization of the modified structure with higher performance are presented. The simulation results obtained provide imperative guidelines for the fabrication of high‐efficiency CZTS solar cells using non‐toxic and earth‐abundant materials. [ABSTRACT FROM AUTHOR]

The effect of the InGaN channel on the performance of high‐electron‐mobility transistors (HEMTs) through the Silvaco Atlas simulator is investigated in detail. It is shown that the 2D electron gas (2DEG) density and carrier confinement of the device can be enhanced by replacing the GaN channel with the InGaN channel. The higher 2DEG density significantly increases the saturation drain current density, thus improving the current drive capability of the device. Meanwhile, better carrier confinement alleviates the short channel effects (SCEs) and traps state‐related current collapse in the GaN buffer, effectively improving the reliability of the device. Better carrier confinement also increases the current gain cutoff frequency (fT) and maximum oscillation frequency (fmax) to 133 and 226 GHz, while the fT and fmax of conventional GaN channel HEMTs are 104 and 167 GHz, respectively. These results indicate that AlInGaN/InGaN HEMTs achieve better performance in direct current (DC) and radio frequency (RF). [ABSTRACT FROM AUTHOR]

To improve the carrier confinement capability and optimize the performance of deep ultraviolet laser diodes (DUV-LDs), we propose the graded rectangular superlattice (GRSL) electron blocking layer (EBL) and the graded trapezoidal superlattice (GTSL) hole blocking layer (HBL) in this paper. Crosslight software is used to simulate and compare the DUV-LDs with rectangular superlattice (RSL) EBL and RSL HBL, GRSL EBL and GRSL HBL, and GRSL EBL and GTSL HBL. The simulation results indicate that GRSL EBL and GTSL HBL increase the carrier concentration in the quantum wells, reduce the electron leakage in the p-type region and the hole leakage in the n-type region, increase the radiation recombination rate, reduce the threshold voltage and threshold current, and increase the electro-optical conversion efficiency and output power of DUV-LDs more effectively. [ABSTRACT FROM AUTHOR]

High-power, broad-area, semiconductor lasers are attractive sources for material processing, aerospace, and laser pumping. The design of the active region is crucial to achieve the required high power and electro-optical conversion efficiency, since the temperature significantly affects the performance of the quantum well, including the internal quantum efficiency and mode gain. In this work, the temperature effects on the active region of a 808 nm high-power semiconductor laser were investigated theoretically and experimentally. The simulations were performed with a Quasi-3D model, which involved complete steady-state semiconductor and carrier confinement efficiency combined with a new mathematical method. The critical aluminum content of the quantum barrier was proposed and the relationship between temperature and various loss sources was disclosed in the temperature range of 213 to 333 K, which provides a reliable reference for the design of epitaxial structures of high-power semiconductor lasers in different operating conditions. Subsequently, the optimized epitaxial structure was determined and used to fabricate standard laser bar chips with a cavity length of 2 mm. The experimental electro-optical conversion efficiency of 71% was demonstrated with a slope efficiency of 1.34 W/A and an injection current of 600 A at the heatsink temperature of 223 K. A record high electro-optical conversion efficiency of 73.5% was reached at the injection current of 400 A, while the carrier confinement efficiency was as high as 98%.

AlGaN based deep ultraviolet (DUV) light-emitting diodes (LEDs), especially with a wavelength below 250 nm, have great application potential in the fields of sterilization and disinfection, gas sensing, and other aspects. However, with the decrease of emission wavelength, performance collapse occurs and the external quantum efficiencies (EQE) of sub-250 nm LEDs are usually below 1% for a long time. Low efficiencies are resulted from problem accumulation of all aspects, including n/p-type doping and contacts, carrier confinements and transports, light extraction, etc. To achieve high EQE of sub-250 nm LEDs, problems and solutions need to be discussed. In this paper, the research progress, development bottlenecks, and corresponding solutions of sub-250 nm LEDs are summarized and discussed in detail.

Herein, the electron–hole wave function overlaps as well as the carrier confinement are both improved by an inversely graded Al‐composition design in the multiple‐quantum‐well (MQW) active region of deep‐ultraviolet light‐emitting diodes (DUV–LEDs). Simulation results show that at a current of 250 mA, the light output power (LOP) of the DUV–LEDs with graded composition MQWs has achieved a remarkable enhancement of 38.7% as compared to that with conventional MQWs, and the efficiency droop is significantly reduced from 32.2% to 9.3%. The enhanced performance is attributed to the increased wave function overlap of the electrons and holes due to the alleviated polarization electric field. Furthermore, the depth of quantum wells (QWs) is increased by the increased polarization‐induced charges and results in a better carrier confinement in the well layers. In addition, the LOP is further enhanced by 20.5% and the efficiency droop is reduced to 6.2% by engineering the last quantum barrier in the graded MQWs, which is attributed to the further reduction in the electron leakage. The proposed structure provides a valuable guideline for the high‐efficiency DUV–LEDs. [ABSTRACT FROM AUTHOR]

Pyramid-shaped InGaN/GaN micro-light-emitting diodes (μ-LEDs) were grown on a sapphire substrate using the selective area growth technique. A stable emission wavelength of a single μ-LED pyramid at 412 nm was observed under an injection current from 0.05 to 20 mA, despite the non-uniformity of the thickness and composition of the multiple quantum wells (MQWs) on the sidewall. An efficient carrier confinement and, thus, a high luminescence intensity were demonstrated in the middle of the sidewall through spatial-resolved cathodoluminescence (CL) characterization and were predicted by theoretical simulations. An ultra-high output power density of 1.37 kW/cm2 was obtained from the single μ-LED pyramid, illustrating its great potential for application in high-brightness micro-displays and in virtual reality and augmented reality (VR and AR) applications.

In this study, systematic structural design was investigated numerically to probe into the cross-relating influences of n-AlGaN layer, quantum barrier (QB), and electron-blocking layer (EBL) on the output performance of AlGaN deep-ultraviolet (DUV) light-emitting diodes (LEDs) with various Al compositions in quantum wells. Simulation results show that high-Al-composition QB and high-Al-composition EBL utilized separately are beneficial for the enhancement of carrier confinement, while the wall-plug efficiency (WPE) degrades dramatically if both high-Al-composition QB and EBL are existing in a DUV LED structure simultaneously. DUV LEDs may be of great optical performance with appropriate structural design by fine-tuning the material parameters in n-AlGaN layer, QB, and EBL. The design curves provided in this paper can be very useful for the researchers in developing the DUV LEDs with a peak emission wavelength ranging from 255 nm to 285 nm.

In deep-ultraviolet (DUV) light-emitting diodes (LEDs), it is difficult to obtain both efficient carrier confinement and high light extraction, which are quite sensitive to optical polarization and other physical parameters. In this paper, characteristics of DUV LEDs with various n-AlGaN layers and quantum barriers (QBs), and various widths of quantum wells (QWs) are investigated. Specifically, the capability of carrier confinement and properties of optical polarization are analyzed in detail. The simulation results show that LED structure with Al0.64Ga0.36N QBs, n-Al0.7Ga0.3N layer, and 4-nm-thick QWs, which has a peak emission wavelength of 284.5 nm at 60 mA, exhibits high internal quantum efficiency of 25% and high degree of optical polarization of 0.874. [ABSTRACT FROM AUTHOR]

Monolayer two-dimensional transitional metal dichalcogenides, such as MoS2, WS2, and WSe2, are direct band gap semiconductors with large exciton binding energy. They attract growing attentions for optoelectronic applications including solar cells, photodetectors, light-emitting diodes and phototransistors, capacitive energy storage, photodynamic cancer therapy, and sensing on flexible platforms. While light-induced luminescence has been widely studied, luminescence induced by injection of free electrons could promise another important applications of these new materials. However, cathodoluminescence is inefficient due to the low cross-section of the electron-hole creating process in the monolayers. Here for the first time we show that cathodoluminescence of monolayer chalcogenide semiconductors can be evidently observed in a van der Waals heterostructure when the monolayer semiconductor is sandwiched between layers of hexagonal boron nitride (hBN) with higher energy gap. The emission intensity shows a strong dependence on the thicknesses of surrounding layers and the enhancement factor is more than 500-fold. Strain-induced exciton peak shift in the suspended heterostructure is also investigated by the cathodoluminescence spectroscopy. Our results demonstrate that MoS2, WS2, and WSe2 could be promising cathodoluminescent materials for applications in single-photon emitters, high-energy particle detectors, transmission electron microscope displays, surface-conduction electron-emitter, and field emission display technologies. [ABSTRACT FROM AUTHOR]

The characteristics of AlGaN-based ultraviolet light-emitting diodes (UV LEDs) with the last quantum well inserted into electron blocking layer(EBL) have been investigated numerically in this study. The simulation results indicate that the light-emitting EBL(LEEBL) can suppress electron leakage better than traditional EBL due to the superior electron confinement and hole injection of the quantum well in LEEBL. Besides, the LEEBL with a quantum well closer to active region can further improve the performance of the UV LED owning to better electron blocking and hole injection for the quantum wells in active region. As a result, the output power of the UV LED with the quantum well located in the middle of LEEBL increases by 17.83% and the utilization of LEEBL with a quantum well located closer to the active region can further enhance the output power by 54.11% compared with traditional UV LED. [ABSTRACT FROM AUTHOR]

We investigated the influence of thickness fluctuations on the carrier dynamics of CdTe/ZnTe quantum dots (QDs). The temperature dependence of both the red-shift in the band-edge transition energy and broadening of the emission line were evaluated using different models. We showed that the quantum confinement effect and thermal escape of the QDs can be extended to significantly higher temperatures. These results were confirmed by using the discrete recombination model to investigate localized and delocalized states. Taking place into the reducing fluctuations of QDs that the thermally activated transition energies and the carrier scattering via phonons are enhanced. [ABSTRACT FROM AUTHOR]

Dislocations exhibit a number of exceptional electronic properties resulting in a significant increase of the drain current of metal-oxide-semiconductor field-effect transistors (MOSFETs) if defined numbers of these defects are placed in the channel. Measurements on individual dislocations in Si refer to a supermetallic conductivity. A model of the electronic structure of dislocations is proposed based on experimental measurements and tight binding simulations. It is shown that the high strain level on the dislocation core-exceeding 10% or more-causes locally dramatic changes of the band structure and results in the formation of a quantum well along the dislocation line. This explains experimental findings (two-dimensional electron gas and single-electron transitions). The energy quantization within the quantum well is most important for supermetallic conductivity. [ABSTRACT FROM AUTHOR]

In this work, the authors present the results of optical characterization of GaAs-based multiple quantum well heterostructures, together with energy band structure analysis. The optical properties were investigated by applying photoluminescence spectroscopy. Structures with GaInNAs, GaInAs and GaNAs multiple quantum wells emitting around 1 μm, grown by atmospheric pressure metalorganic vapor phase epitaxy, were compared in this work. The role of nitrogen in quantum well carriers confinement potential was analysed. The photoluminescence intensities of the samples were correlated with the analysis of energy band structures and the overlaps of the carriers' wave functions. In addition, the main carrier activation energies were estimated based on photoluminescence temperature dependence and the Arrhenius plots analysis. It was deduced that the thermal photoluminescence decay is most probably related to the escape of electrons whereas the holes, independently of the potential well depth, are additionally confined by the local inhomogeneities or by the Coulomb interaction with the confined electrons. [ABSTRACT FROM AUTHOR]

Dislocations exhibit a number of exceptional electronic properties resulting in a significant increase of the drain current of metal-oxide-semiconductor field-effect transistors (MOSFETs) if defined numbers of these defects are placed in the channel. Measurements on individual dislocations in Si refer to a supermetallic conductivity. A model of the electronic structure of dislocations is proposed based on experimental measurements and tight binding simulations. It is shown that the high strain level on the dislocation core—exceeding 10% or more—causes locally dramatic changes of the band structure and results in the formation of a quantum well along the dislocation line. This explains experimental findings (two-dimensional electron gas and single-electron transitions). The energy quantization within the quantum well is most important for supermetallic conductivity.

In this work, the InGaN/AlGaN multiple-quantum-well (MQW) near-ultraviolet (UV) light-emitting diodes (LEDs) with different aluminum compositions in the barrier layers are investigated and fabricated. The aluminum compositions of LED I, II, and III are 0, 2.5, and 3.85%, respectively. The light output powers of LED I, II, and III at an injection current of 350 mA are 95.46, 135.48 mW, and 179.54 mW, respectively. The light output power measured from LED III was 88% larger than that of LED I. The peak external quantum efficiency was enhanced from 9.24 to 17.26%. This result was attributed to the improvement of carrier confinement in the active region by using AlGaN-based barrier layers. The hot-cold effect of LEDs as functions of junction temperature currently is a very important key issue for actual application to LEDs. As the temperature increased, the injected carriers became excited and easily escaped from the active layer. Thus, the light output power of the LED decreased as the temperature increased. Compared with LED I and LED II, the light output power of LED III with better carrier confinement was decreased more slowly with increasing temperature. [ABSTRACT FROM AUTHOR]

We have investigated the impact of surface recombination on the effective carrier injection efficiency and the Joule heating of axial InGaN/GaN nanowire light-emitting diodes (LEDs). The results reveal that the carrier injection efficiency of such devices is extremely low (<;10%), due to the severe carrier loss through nonradiative surface recombination. It is further observed that the thermal resistance of typical nanowire LEDs is comparable with, or lower than that of their planar counterparts, in spite of the reduced thermal conductivity of nanowires. The poor carrier injection efficiency, however, leads to significantly elevated junction temperatures for nanowire LEDs. We have further demonstrated, both theoretically and experimentally, that the carrier injection efficiency can be significantly improved in p-doped nanowires, due to the downward surface band bending, and in InGaN/GaN/AlGaN dot-in-a-wire core-shell nanoscale heterostructures, due to the superior carrier confinement offered by the large bandgap AlGaN shell. This paper offers important insight for the design and epitaxial growth of high-performance nanowire LEDs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Effect of strain and exciton carrier confinement on SML QD size distribution is studied. • Sample splits with varying monolayer (ML) coverage, X (0.3, 0.5) and QD stacks, Y (4, 6, 8) were considered. • PL of 0.5 ML showed efficient carrier localization, while 0.3 ML by phonons. • Raman and HRXRD analysis helped us calculate the In% inside SA In x Ga 1− x As layers. • Best results were achieved for 0.5 ML with 4 QD stacks with GS PL peak at 1.19 eV and reduced defects. Strain – induced intermixing in sub – monolayer (SML) quantum dots (QDs) affects primarily the dot size distribution in an erratic way and also the inter – dot coupling efficiency for carrier transport. In this study, we have explored the role of strain and carrier confinement effects in order to control the dot size distribution by varying InAs QDs coverage (X: 0.3 and 0.5 ML) and stacks (Y: 4, 6, and 8) simultaneously. The size variation affects the position of localized levels inside QDs primarily as it is the inter – dot coupling that decides the luminescence efficiency. Next, through multiple stacking of QD layers, strain variation becomes inhomogenous that facilitate a higher degree of In – Ga intermixing which necessitates to estimate the amount of Indium (%) present inside such In–rich islands to progress for a superior optical performance. Hence, we combine and address these above concerns in great detail. The 20 K ground-state (GS) photoluminescence (PL) energy for 0.3 and 0.5 ML samples were centered at 1.24–1.33 eV, and 1.11–1.19 eV respectively. The PL linewidth and activation energy variation with temperature validated that there exists two possible thermal escape pathways for carrier recombination. Besides, PL – excitation (PLE) studies comprehended the influence of phonon and excited states (ES) in the samples. Raman analysis helped us calculate the In% inside QDs by figuring out the shift in InAs QD phonon modes (amount of compressive strain). Furthermore, the structural analysis by high-resolution X-ray diffraction (HRXRD) was done to calculate the strain moderated defect density and also the effect of in – plane compressive strain to the reduction in quantum confinement. The increase in compressive strain inside QDs caused more In–Ga intermixing in 0.3 ML samples and higher defect densities. Altogether we see that sample with 0.5 ML, 4 stacks showed vertically-correlated dot growth (from HR-XTEM) with minimum strain (−0.03383 a.u.), dislocation density (4.887 x 1011 cm−2) and higher In content (62.41%). This high degree of excitonic carrier confinement and strain tuning makes SML QDs an attractive candidate for room-temperature (RT) operable photodetector (PD) devices. [ABSTRACT FROM AUTHOR]

Abstract: The pinch-off current leakage characteristics of Al x Ga1− x N/GaN HEMTs using semi-insulated GaN or Al0.04Ga0.96N buffer layers have been fully investigated. Their gate-drain leakage current densities are only 0.2 and 0.075mA/mm at V GD of 100V respectively, which guarantees excellent reverse Schottky breakdown characteristic. Meanwhile, by introducing low-Al Al x Ga1− x N high-resistivity layer, it shows not only a much sharper sub-threshold turn off characteristic with a higher transconductance peak value, but also very lower deep-depletion leakage current. And its better carrier confinement under high V DS greatly improves both the small-signal characteristic and microwave power performance of GaN HEMT devices. In addition, electrical reliability of Al x Ga1− x N/GaN HEMTs at high voltage operation has been greatly improved. [Copyright &y& Elsevier]

To examine the matrix effect on the light emission of Si nanocrystal (Si-NC), we investigated the photoluminescence (PL) of Si-NC from multilayered samples of Si/SiO and SiO/SiO and single-layered pure Si thin films, which had all been annealed in nitrogen at 1,100 °C for 1 h so as to form Si-NCs. The size range of Si-NC is 1-10 nm. It was found that the density of Si-NC in the pure Si> that in Si/SiO> that in SiO/SiO, but the PL intensity of Si-NC from pure Si< that from Si/SiO< that from SiO/SiO. On the other hand, the PL intensity of Si-NC from Si/SiO sample is higher than that from Si/SiN one. All these results are related to the difference in matrix surrounding Si-NCs, which causes differences in carrier confinement or/and interface state. The results suggest that for light emission of Si-NC, the matrix effect is determinative, and can be more important than the density of Si-NC itself. [ABSTRACT FROM AUTHOR]

The impact of the Si cap/SiGe layer on the Hf-based high-k /metal gate SiGe channel pMOSFET performance and reliability has been investigated. We proposed an optimized strain SiGe channel with a Si cap layer to overcome the Ge diffusion and confine the channel carriers in the strained SiGe layer without the formation of a significant parasitic channel at the interface. With this optimized Si/SiGe stack channel, a high-performance Hf-based high-k/metal gate SiGe pMOSFET can be obtained with an appropriate VTH ( \sim0.3 V), low C–V hysteresis (< 5 mV), and better ION - IOFF, VTH rolloff, and VTH stability. By the way, the related interface trap density in the high-k gate stack layer can also be reduced, thus improving the device's NBTI and HCI stressing-induced reliability. [ABSTRACT FROM PUBLISHER]

Abstract: FinFETs with ultra-large height-to-width ratio have been processed on (110) bulk silicon wafers by employing crystallographic etching of silicon with TMAH, which results in nearly vertical sidewalls with a (111)/〈112〉 surface orientation. Tall fins, which corresponds to wide transistor channels per single fin offer more efficient use of the silicon area and improved performance for multi-fin devices in high-frequency analog applications. N-channel FinFETs with 1.9-nm-wide fins demonstrate the downscaling potential of the technology and devices with a height of the active part of the fin of 625nm have the largest aspect-ratio of the fins reported thus far. Both devices with highly and moderately scaled fin-widths exhibit excellent subthreshold performance while electrons have higher mobility in 15-nm-wide FinFETs, which gives them larger on-state currents. The comparison between FinFETs and wide tri-gate devices shows that FinFETs have better current drivability in this simple process, even with larger source/drain series resistances. The differences in threshold voltage and low-field electron mobility between 1.9-nm-wide and 15-nm-wide FinFETs have been related to the increase in subband energies due to carrier confinement in the extremely narrow fins. [Copyright &y& Elsevier]

Total internal reflection optical switches offer a switching operation which can be wavelength insensitive, thermally stable and polarisation independent. The implementation of such a switch based upon carrier injection in silicon is difficult due to the long diffusion lengths of injected free carriers. In this paper experimental results are presented which show that a reflective type switching operation is obtainable if a barrier formed of defective silicon is used to reduce free carrier diffusion. [ABSTRACT FROM PUBLISHER]

Abstract: This paper examines the DC power requirements of PIN diodes which, with suitable applied DC bias, have the potential to reflect or to permit transmission of millimetre wave energy through them by the process of inducing a semiconductor plasma layer in the I region. The study is conducted using device level simulation of SOI and bulk PIN diodes and reflection modeling based on the Drude conduction model. We examined five diode lengths (60–140μm) and seven diode thicknesses (4–100μm). Simulation output for the diodes of varying thicknesses was subsequently used in reflection modelling to assess their performance for 100GHz operation. It is shown that substantially high DC input power is required in order to induce near total reflection in SOI PIN diodes at 100GHz. Thinner devices consume less DC power, but reflect less incident radiation for given input power. SOI diodes are shown to have improved carrier confinement compared with bulk diodes. [Copyright &y& Elsevier]

Abstract: A blue organic light emitting device (OLED) with improved efficiency and good color purity is reported. The highest occupied molecular orbital (HOMO) level of the hole transport layer (HTL) and that of the emissive layer (EML) differs by 0.3eV. This energy level mismatch confines the carriers at the HTL/EML interface. Conventional devices have only one HTL/EML interface, with a current efficiency of 2.9cd/A. Without adding a separate hole blocking layer, incorporating multi-layers of the same HTL and EML increases this efficiency to 5.8cd/A, with only a small increase in operating voltage yielding increased power efficiency also. But, there are an optimum number of layers, beyond which efficiency loss results. Also, including the multilayer structure simultaneously improves the blue color co-ordinates. To gain insight into the role of multilayer structures in modifying charge transport and recombination zone a simulator was developed. The simulated results could qualitatively explain the experimental observations. [Copyright &y& Elsevier]

Abstract: We report the influences of quantum dot (QD) shape on the lasing characteristics such as threshold current, slope efficiency, and wavelength stability. The average heights of the shape-engineered InAs/InAlGaAs QDs (SEQDs) and the conventionally-grown Stranski-Krastanov InAs QDs (CQD) were 10±0.5 and 2.5±0.5 nm, respectively. For the cavity length of 0.5 mm, the threshold current of the laser diodes (LDs) with the InAs/InAlGaAs SEQDs as an active layer (SEQD-LD) was decreased by 3.6 times smaller than that of the LDs with the InAs CQDs (CQD-LD). Also the slope efficiency for the SEQD-LD was increased to 0.15 from 0.087 W/A of the CQD-LD. While the lasing wavelength of the CQD-LD was red-shifted by 0.032 μm with increasing cavity length from 0.5 to 0.75 mm, the lasing emission of the SEQD-LD was red-shifted only by 0.012 μm with increasing cavity length from 0.5 to 1.5 mm. From these results, the gain of the QDLDs was enhanced by increasing the height of the QDs due to the enhancement in the confinement of the carrier wave-functions. [Copyright &y& Elsevier]

Total internal reflection optical switches structures are well known. However, previously reported switches based upon carrier injection have suffered from the diffusion of carriers within the guiding layer leading to inefficient reflection. While some attempts have been made to restrict the diffusion of carriers in devices fabricated in materials other than silicon, carrier diffusion has still been possible. In this paper, we propose the use of a thin SiO2 barrier around the carrier injection region to improve the performance of the device. Modeling data has shown that high-performance switching is possible by confining the carriers in this way. Modeling suggests that switching times of the order of 5 ns can be achieved with a switching current of the order of 30 mA. [ABSTRACT FROM PUBLISHER]

To improve the pinched-off characteristics of an AIGaN/GaN heterojunction field effect transistor (HJFET), the conduction band potential of an incorporated A1x Ga1-xN buffer is designed to be upwardly convex in a band diagram. This approach utilizes the polarization effects specific to GaN-based materials by lowering the Al content x from 30% to 5% almost linearly toward the front side. Fabricated field effect transistors (FETs) adopting the designed buffer have demonstrated the following advanced characteristics in comparison to those of a FET adopting a conventional GaN buffer: less than one-tenth of the buffer leakage current, a gate-to-drain breakdown voltage BVgd twice or more as high, and remarkably improved carrier confinement and pinched-off behavior. The FETs are operated in an enhancement mode with a gate-to-channel distance thick enough to prevent tunneling current through the gate. [ABSTRACT FROM AUTHOR]

The effect of quantum confinement in thin silicon-on-insulator double-gate MOSFETs has been directly determined from subthreshold current measurements for the first time. By comparing temperature-dependent subthreshold characteristics of p-type devices with different silicon layer thicknesses, the offset in the valence band edge induced by spatial carrier confinement in these very thin silicon layers was measured electrically. Changes in the band structure are important for future CMOS devices such as FinFETs. [ABSTRACT FROM AUTHOR]

In this study we analyzed the envelope functions obtained by solving the effective-mass Schrödinger equation including the non-parabolicity of the valence band in p-type FD-SOI devices. In order to carry out this task, we used two different algorithms to solve the effective-mass Schrödinger equation in barriers, and calculated the envelope functions and eigenenergies yielded by these methods for several states along the subbands. This study enabled us to propose a method for selecting the most appropriate envelope functions for each subband. Finally, we quantified the differences in phonon and interface-roughness scattering rates resulting from using the envelope function proposed rather than that obtained by simpler approaches in barriers. [ABSTRACT FROM AUTHOR]

We report distinct optical/electrical properties inherent to build-in nanostructures in transparent oxide based materials, oxychalcogenides LaCuOS and LaCuOSe having naturally formed multi-quantum well structures and 12CaO·7Al2O3 (C12A7) with a unique nanoporous structure. LaCuOSe doped with Mg ions exhibit degenerative p-type conduction presumable due to “modulation doping mechanism” with a high mobility of 4.0 cm2 V-1 s-1 even at high hole concentration (∼2×1020 cm-3). The room temperature exciton, having a large binding energy (∼50 meV) due to the confinement effect of carriers in the CuS or CuSe layer, induces a large optical nonlinearity at room temperature (RT) (χ(3) = 2–4×10-9 esu) near the absorption band. The H- ion entrapped in nanosize cages in C12A7 lattice causes an persistent conversion at RT from an electric insulator (<10-10 S cm-1) to a semiconductor (0.3–100 S cm-1) by capturing electrons photo-ionized from H- ions in the cages. This is a first electronic conductor based on main group light metal oxides. [Copyright &y& Elsevier]

Nitride-based Al0.24Ga0.76N/GaN heterostructure field effect transistors (HFETs) with carrier confinement layers were successfully fabricated. It was found that the source–drain (S–D) leakage currents of the HFETs with carrier confinement layers were much smaller. It was also found that we could enhance the two dimensional electron gas (2DEG) carrier mobility from 1070 to 1180 cm2/V/s by the insertion of a Mg-doped semi-insulating carrier confinement layer with a Cp2Mg flow rate of 2.36×10-8 mole/min. At the same time, we could also achieve a smoother sample surface. The dc and rf characteristics of these HFETs were also found to be good. [Copyright &y& Elsevier]

Nanostructures naturally formed in oxide semiconductor crystals are discussed in relation to their electronic structure and properties. Three different crystals are studied: (i) layered oxychalcogenides LnCuOCh (Ln=lanthanide, Ch=chalcogen), (ii) homologous series layered oxides RMO3(ZnO)m (R=In, Lu etc., M=In, Ga etc., m=integer), and (iii) nanoporous crystal 12CaO7 · Al2O3 (C12A7). Coexistence of moderately large mobility, intense photoluminescence arising from room-temperature exciton and high-density hole is explained by a natural modulation doping structure in LnCuOCh. C12A7 exhibits different properties by replacing free O2- ions anions clathrated in its subnanometer-sized cages with O-, H-, and electron. The electronic structures of the clathrated anions were investigated by ab initio calculations and discussed in terms of possible quantum structures and applications. [Copyright &y& Elsevier]

In this study, a triangular-barrier and a double-barrier structure are combined to form a double-barrier-emitter triangular-barrier optoelectronic switch (DTOS). In the structure center of the triangular barrier, a p-type delta-doped quantum well is inserted to enhance the hole confinement. Owing to the resonant tunneling through the double-barrier structure and avalanche multiplication in the reverse-biased junction, N-shaped and S-shaped negative-differential-resistance (NDR) phenomena occur in the current-voltage (I-V) characteristics under normal and reverse operation modes, respectively. The NDR characteristics show variations from dark to illumination conditions. Temperature effects on the NDRs of the DTOS are also obvious. The illumination and temperature influences on the device characteristics are investigated in this paper. [ABSTRACT FROM AUTHOR]

The 400-nm In0.05Ga0.95N-GaN MQW light-emitting diode (LED) structure and In0.05Ga0.95N-Al0.1Ga0.9N LED structure were both prepared by organometallic vapor phase epitaxy. It was found that the use of Al0.1Ga0.9N as the material for barrier layers would not degrade crystal quality of the epitaxial layers. It was also found that the 20-mA electroluminescence intensity of InGaN-AlGaN multiquantum well (MQW) LED was two times larger than that of the InGaN-GaN MQW LED. The larger maximum output intensity and the fact that maximum output intensity occurred at larger injection current suggest that AlGaN barrier layers can provide a better carrier confinement and effectively reduce leakage current. [ABSTRACT FROM PUBLISHER]

Pyramid-shaped InGaN/GaN micro-light-emitting diodes (μ-LEDs) were grown on a sapphire substrate using the selective area growth technique. A stable emission wavelength of a single μ-LED pyramid at 412 nm was observed under an injection current from 0.05 to 20 mA, despite the non-uniformity of the thickness and composition of the multiple quantum wells (MQWs) on the sidewall. An efficient carrier confinement and, thus, a high luminescence intensity were demonstrated in the middle of the sidewall through spatial-resolved cathodoluminescence (CL) characterization and were predicted by theoretical simulations. An ultra-high output power density of 1.37 kW/cm2 was obtained from the single μ-LED pyramid, illustrating its great potential for application in high-brightness micro-displays and in virtual reality and augmented reality (VR and AR) applications. [ABSTRACT FROM AUTHOR]

We investigate the effects of structural asymmetry on the electronic and optical properties of indium gallium nitride (InGaN) quantum wells (QW's). Using a pulsed current excitation technique, spectral blue shift as large as 80 meV is observed in a strained 3.0-nm In0.2Ga0.8N QW as the pulsed current increases from 1 mA to 1 A. Based on a self-consistent calculation, we are able to quantify a gain competition process among the interactions of piezoelectricity, many-body, charge screening, and band filling effects. Such interactions are shown to provide a mechanism for shaping the QW confined potential such that superior carrier confinement and charge screening of the piezoelectric field can be obtained in the asymmetric InGaN QW. At high carrier injection of Ninj>2×1019 cm-3, a tenfold increase in the TE-polarized optical gain can be achieved by using the asymmetric GaN-InGaN-AlGaN QW instead of the symmetric InGaN-AlGaN QW. Due to the diminishing of piezoelectricity-induced quantum-confined Stark effect, the calculated optical gain spectra of the asymmetric InGaN QW exhibit a spectral blue shift with respect to those of the symmetric InGaN QW [ABSTRACT FROM PUBLISHER]