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<i>β</i> -Ga <sub/>2</sub> O <sub/>3</sub> thin film grown on sapphire substrate by plasma-assisted molecular beam epitaxy
摘要： Monoclinic gallium oxide (Ga2O3) has been grown on (0001) sapphire (Al2O3) substrate by plasma-assisted molecular beam epitaxy (PA-MBE). The epitaxial relationship has been confirmed to be [010](ˉ201)β-Ga2O3||[1ˉ100](0001)Al2O3 via in-situ reflection high energy electron diffraction (RHEED) monitoring and ex-situ X-ray diffraction (XRD) measurement. Crystalline quality is improved and surface becomes flatter with increasing growth temperature, with a best full width at half maximum (FWHM) of XRD ω-rocking curve of (ˉ201) plane and root mean square (RMS) roughness of 0.68° and 2.04 nm for the sample grown at 730 °C, respectively. Room temperature cathodoluminescence measurement shows an emission at ~417 nm, which is most likely originated from recombination of donor–acceptor pair (DAP).
关键词： CL measurement,β-Ga2O3,sapphire substrate,PA-MBE,crystalline quality
更新于2025-09-23 15:22:29
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[IEEE 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Kyoto, Japan (2018.7.9-2018.7.13)] 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Depth profile of ZnAl<inf>2</inf> O<inf>4</inf> layer on sapphire substrate by cathodoluminescence
摘要： ZnAl2O4 for ultraviolet emitting phosphor prepared by deposition of ZnO on c-sapphire substrate and thermal diffusion process. The deflections of Zn and Al atoms in the films were confirmed by cathodo-luminescence properties. The CL intensity of ZnAl2O4 was not saturated from the film annealed for 100 hours, however, the saturation of UV emission was observed under anode voltage of 8 kV in the film annealed for 200 hours. It is thought that the thickness of ZnAl2O4 film became thinner by longer annealing at high temperature because of Zn re-evaporation. From cross-sectional FE-SEM observation, it was confirmed that the correct thickness and atomic distributions in the film. Since the ZnAl2O4 film thickness of the sample annealed for 100 hours was about 1 μm by FE-SEM, it was suitable the penetration depth of the electron into ZnAl2O4 layer
关键词： Sapphire substrate,Thermal distribution,ZnAl2O4,Ultra-Violet emission
更新于2025-09-23 15:21:21
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Effect of Interface State Density of the AlGaN Electron Blocking Layer/GaN Barrier Layer in InGaN Blue Light-Emitting Diodes
摘要： Herein, two kinds of blue InGaN light-emitting diodes (LEDs) were compared in order to understand the effect of the strain originating from two different sapphire substrates. One of the LED types was grown on a patterned sapphire substrate (PSS), and the other was grown on a conventional sapphire substrate (CSS). The internal strains biased on InGaN quantum wells were compared by studying the time-resolved photoluminescence and the electroreflectance. Through analysis of the dynamic capacitance dispersion measurements, the relation between the trap states and trap density of the AlGaN electron blocking layer/GaN barrier interface above the InGaN quantum wells can be understood in great detail. The trapped charges of the CSSs have faster response times than those of the PSSs; this is attributed to the stronger piezo-field, which induces the AlGaN EBL/GaN barrier interface trap states to be effectively located at shallower levels from the conduction band.
关键词： Strain,Patterned sapphire substrate,InGaN quantum wells
更新于2025-09-23 15:19:57
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Light Extraction Efficiency Optimization of AlGaN-Based Deep-Ultraviolet Light-Emitting Diodes
摘要： Using finite-difference time-domain method, the light extraction efficiency (LEE) of AlGaN-based deep-ultraviolet light-emitting diodes (DUV LEDs) is investigated. Simulation results show that compared to flat sapphire substrate, the nano-patterned sapphire substrate (NPSS) expands the extraction angles of top surface and sidewalls. As a result, the LEE of transverse-magnetic (TM) polarized light is improved significantly. Roughening on the backside of n-AlGaN surface significantly enhances the LEE of top surface of thin-film flip-chip DUV LEDs. However, the LEE of sidewalls of thin-film flip-chip DUV LEDs is greatly weakened. For bare DUV LED, the LEE of flip-chip LED on NPSS is estimated to be about 15%, which is around 50% higher than that of thin-film flip-chip DUV LED with roughening on the backside of n-AlGaN surface.
关键词： AlGaN,nano-patterned sapphire substrate,light-emitting diodes,deep-ultraviolet,light extraction efficiency
更新于2025-09-23 15:19:57
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Thermally annealed wafer-scale h-BN films grown on sapphire substrate by molecular beam epitaxy
摘要： The effect of high temperature annealing (HTA) on crystalline quality improvement of h-BN films grown on sapphire substrates has been investigated. It is found that BN grown using conventional molecular beam epitaxy is disordered due to the growth temperature below 1000 °C. By annealing at a temperature of 1700 °C, thermodynamically stable crystalline h-BN could be obtained at wafer scale, where diffusion of atoms in the as-grown BN film is enhanced and the structural defect density decreases. The crystalline h-BN has been confirmed by x-ray diffraction, Raman scattering, and atomic force microscopy measurements. This work demonstrates that HTA is a simple and effective way to achieve wafer-scale crystalline h-BN films, which have numerous potential applications in next-generation two-dimensional devices and flexible III-nitride optoelectronic devices.
关键词： crystalline quality,molecular beam epitaxy,sapphire substrate,h-BN films,high temperature annealing
更新于2025-09-19 17:13:59
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Effects of interfaces and current spreading on the thermal transport of micro-LEDs for kA-per-square-cm current injection levels
摘要： The three-dimensional thermal characteristics of micro-light-emitting diodes (mLEDs) on GaN and sapphire substrates were studied with forward-voltage methods, thermal transient measurements, and infrared imaging. The mLEDs on the GaN substrate showed an approximately 10 °C lower junction temperature and smaller amplitude of the K factors than those on the sapphire substrate under the current injection level of 4 kA cm?2. The thermal transient measurement showed that the spreading thermal resistances of the mesa, the GaN epilayer, and the interface of the GaN/substrate were reduced significantly for mLEDs on the GaN substrate because of the high-quality GaN crystal and the interfaces. The infrared thermal images showed lower total average junction temperatures and more uniform temperature distributions for the mLEDs on the GaN substrate, which were also simulated with APSYS software. The thermal transport mechanisms are discussed for the lateral and vertical directions in the mLEDs.
关键词： sapphire substrate,micro-light-emitting diodes,GaN substrate,junction temperature,thermal transport,infrared imaging,APSYS simulation
更新于2025-09-11 14:15:04
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Repeatable Room Temperature Negative Differential Resistance in AlN/GaN Resonant Tunneling Diodes Grown on Sapphire
摘要： Resonant tunneling diodes (RTDs) are candidates for high power terahertz oscillators, and form the basis for understanding the quantum confinement and vertical transport in quantum structures such as quantum cascade lasers and quantum cascade detectors. In this work, repeatable negative differential resistance (NDR) is achieved in AlN/GaN RTDs grown on sapphire substrate by plasma-assisted molecular-beam epitaxy. Two reproducible NDR regions sequentially following two preresonance replicas are demonstrated at room temperature. A current region exhibiting negative correlation with temperature and oscillation-like features is first identified under reverse bias, which is interpreted as a combined contribution of weak resonant tunneling channels through different bound states in the well. The revealed peak-to-valley current ratio ranges from 1.1 to 1.8, and peak current density ranges from 5 to 164 kA cm?2. Using an analytic model, resonant tunneling transports in both bias directions are quantitatively characterized and show good agreements with experiment results, demonstrating the capability of accurate quantum transport control using III-nitride grown on sapphire substrate. The findings will promote the implementation of low cost III-nitride monolithic microwave circuits and resonant tunneling structures based on sapphire, SiC, and even silicon substrates.
关键词： sapphire substrate,AlN/GaN resonant tunneling diodes,repeatable negative differential resistance
更新于2025-09-10 09:29:36
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[IEEE 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Paris, France (2018.7.8-2018.7.13)] 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Observation of Solder Layers for PJVS Chips Formed with Supersonic-Soldering Method
摘要： The InSn solder layers between Si chips for programmable Josephson voltage standard (PJVS) and sapphire substrates for thermal contact were observed using a scanning acoustic microscope. The solder layers were formed with a supersonic-soldering method in several conditions. Based on the results of the observations, the void ratio in the solder layers was estimated to be approximately 20 % – 40 %, which is much improved in comparison to that obtained with a conventional soldering method of approximately 80 %. We are now trying to measure the influence of these soldering methods on the thermal contact of PJVS chips.
关键词： void,InSn solder,thermal contact,Josephson voltage standard chip,supersonic solder,sapphire substrate
更新于2025-09-10 09:29:36
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Suppressing the Initial Growth of Sidewall GaN by Modifying Micron-Sized Patterned Sapphire Substrate with H3PO4-Based Etchant
摘要： Micron-sized patterned sapphire substrates (PSS) are used to improve the performance of GaN-based light-emitting diodes (LEDs). However, the growth of GaN is initiated not only from the bottom c-plane but also from the sidewall of the micron-sized patterns. Therefore, the coalescence of these GaN crystals creates irregular voids. In this study, two kinds of nucleation layers (NL)—ex-situ AlN NL and in-situ GaN NL—were used, and the growth of sidewall GaN was successfully suppressed in both systems by modifying the micron-sized PSS surface.
关键词： growth of GaN,micron-sized patterned sapphire substrate,sidewall GaN
更新于2025-09-09 09:28:46