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GaN grown by metalorganic vapor phase epitaxy
摘要： We report on residual impurities in semi-polar (3031) and (2021) GaN homo-epitaxial layer grown by metal-organic chemical vapor deposition. The (3031) and (2021) GaN layer showed atomically smooth surface and clear steps toward [0001] and [000-1], respectively. The residual impurity concentrations of oxygen and carbon were below the detection limit of secondary-ion mass spectroscopy. Low-temperature photoluminescence revealed that (2021) GaN layer consisted free excitons and Si donor bound excitons, along with two-electron satellite lines and longitudinal optical (LO) phonon coupling transitions. The results indicate semi-polar (3031) and (2021) GaN epitaxial layers are promising candidates in obtaining a high quality GaN drift layer for vertical GaN devices.
关键词： B2. Semiconducting III-V materials,A3. Metalorganic chemical vapor deposition,B1. Nitrides,A1. Crystal structure,A1. Impurities
更新于2025-09-19 17:15:36
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MOCVD Growth and Characterization of InN Quantum Dots
摘要： Metal-polar InN quantum dots (QDs) are grown by metalorganic chemical vapor deposition at temperatures between 500 and 600 °C. Dot densities between 4 × 10^8 and 4 × 10^10 cm^-2 are observed. InN QDs exhibit room-temperature photoluminescence (PL) with peak wavelengths from 1100 to >1550 nm. GaN cap layers grown on InN QDs have little effect on either peak PL wavelength or intensity, a step toward creating multilayer structures for InN QD devices.
关键词： quantum dots,thin films,metalorganic chemical vapor deposition,nitrides
更新于2025-09-19 17:13:59
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Study of Optical Properties of Surface Layers Produced by Laser Surface Melting and Laser Surface Nitriding of Titanium Alloy
摘要： This study measured optical properties, such as specular, di?use, and total re?ection for 808 nm wavelength, characteristic for high power diode lasers radiation, from the surface of titanium alloy Ti6Al4V at delivery conditions, polished, and oxidized. Moreover, the optical properties of surface layers produced by high power direct diode laser (HPDDL) melting and nitriding were determined. Additionally, a methodology for determining the value of absorption for 808 nm wavelength of the HPDDL radiation on the surface of a melt pool during laser surface melting and nitriding of titanium alloy was proposed. The results show that the distinct di?erences in absorption a?ect the heat transfer, thermal conditions of laser heating and thereby the penetration depth during laser melting and nitriding of the titanium alloy.
关键词： high power diode laser,absorption,titanium nitrides,re?ectivity
更新于2025-09-16 10:30:52
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Single photon emission from top-down etched III-nitride quantum dots
摘要： We report the single photon emission properties of III-nitride quantum dots (QDs) fabricated by electrochemical etching method from an epitaxial wafer. Through such top-down fabrication, QDs with diameters of sub-10 nm are obtained, embedded in GaN nanoneedles. Owing to the size induced quantum con?nement effect, the photoluminescence of the QDs exhibits a 3.35 nm blueshift compared with that of the epitaxial wafer. At low temperature, a second order correlation value down to 0.123 is observed, indicating a high-purity single photon emission. Our QDs manifest single photon emission at a temperature up to 130 K with a high degree of polarization of 0.69, comparable to those QDs synthesized by epitaxial growth. Our work demonstrates single photon emission are viable in top-down QDs by electrochemical etching III-nitride wafers.
关键词： single photon emission,III-nitrides,quantum dot,electrochemical etching
更新于2025-09-16 10:30:52
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Effects of Mg and Si doping in the guide layers of AlGaN-based ultraviolet-B band lasers
摘要： We investigated the effects of Si and Mg doping concentrations in the guide layers on the threshold power density of an AlGaN-based optically pumped ultraviolet-B band (UV-B) laser. For Si, a decrease in the threshold power density required for laser oscillation was confirmed at doping concentrations up to an order of 1017 cm?3. However, an increase was confirmed at high concentrations of approximately 1018 cm?3. For Mg doping, no decrease in the threshold power density of the optically pumped laser was confirmed even at low Mg concentrations, and it increased rapidly at 1018 cm?3. These results were characterized by weakly excited photoluminescence and variable stripe length, indicating that they were due to changes in optical gain with increasing or decreasing internal quantum efficiency and changes in internal loss. This suggests that Mg doping of the guide layer in UV-B lasers should be lower than 1018 cm?3 to realize low-threshold power density lasers. On the other hand, doping on an order of up to 1017 cm?3 for Si was effective at reducing the threshold power density. This indicates that the threshold power density increases if it is too high. These results could provide guidance for designing UV-B lasers in the future.
关键词： Doping,Laser diodes,Metaloganic vapor phase epitaxy,Impurities,Nitrides
更新于2025-09-16 10:30:52
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Kinetic Monte Carlo simulations of the dynamics of a coupled system of free and localized carriers in AlGaN
摘要： A model for the dynamics of a coupled system of free and localized carriers in semiconductors with strong carrier localization is suggested. Kinetic Monte Carlo technique is exploited for simulations. The model is verified by fitting the simulated and experimental temperature dependences of photoluminescence (PL) band intensity, peak position, and band width, and the carrier density dependence of PL efficiency in AlGaN quantum wells. The influence of carrier localization conditions on the dominating carrier migration and recombination processes is revealed. The efficiency droop effect is shown to be caused by peculiarities of carrier localization without significant influence of Auger recombination.
关键词： AlGaN,nitrides,carrier localization,efficiency droop,Monte Carlo simulations
更新于2025-09-12 10:27:22
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[IEEE 2019 Global LIFI Congress (GLC) - Paris, France (2019.6.12-2019.6.13)] 2019 Global LIFI Congress (GLC) - Design and Fabrication of Micro LEDs for High Data Rate LiFi Communications
摘要： In this research, we have investigated P-I-N structures based on InGaN/GaN materials suitable for different size and adapted to the requirements of device characterization. The fabrication has been performed using different designs. Besides, the optimization of the fabrication process has been performed for multi scaled device fabrication (ranging from 5×5 μm2 to 100×100 μm2) in terms of photolithography, etching, metal deposition and passivation. We have considered μ-photodiodes with planar and vertical configurations. Design and fabrication of specific coplanar RF electrical transmission lines have been performed in order to reduce the influence of parasitic capacitances. We have therefore evaluated the size effect on capacitance which affects the speed of the devices, and consequently the cut-off frequency. The reported cut-off frequency @ -3dB has been evaluated as 1.5 GHz for a diameter of 25μm. This result indicates a potential response for LiFi needs as a part of optical wireless secured communication technology.
关键词： LiFi,devices fabrication,frequency,III-nitrides
更新于2025-09-12 10:27:22
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[IEEE 2019 European Space Power Conference (ESPC) - Juan-les-Pins, France (2019.9.30-2019.10.4)] 2019 European Space Power Conference (ESPC) - High Efficiency Lattice-Matched 4J Space Solar Cells on GaAs
摘要： A lattice-matched four-junction solar cell on a GaAs substrate, for space applications, is demonstrated. The solar cell incorporates MBE grown GaInP, GaAs, GaInNAsSb and GaInNAsSb junctions with band-gaps of 1.9 eV, 1.4 eV, 1.2 eV and 0.9 eV, respectively. For AM0 illumination, the cell exhibited a maximum efficiency of 27%. For this performance, a high collection efficiency for the bottom cell is required. The high efficiency and current generation for the four-junction solar cell is primarily enabled by achieving a very low background doping level (~5×1014 cm-3) and high charge carrier lifetimes (2-4 ns) for the GaInNAsSb bottom junction. Achieving an efficiency of 33% is deemed possible by further reduction of reflection, shadowing and transmission losses.
关键词： four-junction solar cell,dilute nitrides,molecular beam epitaxy
更新于2025-09-12 10:27:22
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Influence of Showerhead–Sample Distance (GAP) in MOVPE Close Coupled Showerhead Reactor on GaN Growth
摘要： The distance between the showerhead and the sample surface (GAP) is one of the main growth parameters of the commonly used research reactor, Close Coupled Showerhead. We examine its influence on the growth rate of GaN layers deposited under various conditions (growth temperature, carrier gas, V/III ratio and growth pressure). Regardless of other growth parameters, increasing the GAP value leads to a reduction in the growth rate.
关键词： nitrides,metalorganic vapour phase epitaxy,epitaxy
更新于2025-09-11 14:15:04
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Dyakonov Surface Electromagnetic Waves in III-Nitride Heterostructures
摘要： Lossless Dyakonov surface electromagnetic waves (DWs) that may be excited at the interfaces between non-polar III-nitride wurtzite semiconductors and optically isotropic dielectrics are considered theoretically. Because of stringent requirements on optical properties of the dielectrics suitable for DW excitation, those of them satisfying the existence conditions of surface electromagnetic waves are selected to operate in pair with AlGaN materials in a wide spectral range. DWs formed at the representative HfO2/AlN and SrTiO3/GaN interfaces are discusses in detail, including their propagation directions, angle bands of existence, and localization lengths of the surface waves near the interfaces.
关键词： field localization,birefringence,surface electromagnetics waves,oxide dielectrics,non-polar III-nitrides
更新于2025-09-10 09:29:36