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Abstract: Optically specular a-plane GaN was grown on r-sapphire substrate by metal–organic chemical vapor deposition (MOCVD). Surface morphology and crystal structure anisotropic behavior related to defects with a specific distribution were characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM). Cathodoluminescence (CL) images and depth-profiling spectra show Basel stacking faults (BSFs) related emission at 3.42eV, yellow band emission at 2.25 and 3.00eV emission bands of the a-plane GaN. From the results of CL and transmission electron microscopy (TEM), the origin of the blue emission band was attributed to donor–acceptor pair (DAP) emission correlated with prismatic stacking faults (PSFs). [Copyright &y& Elsevier]

Abstract: In this paper, three GaN epilayers grown on commercially available cone-patterned sapphire substrates (PSS) by Metal Organic Vapor Phase Epitaxy (MOVPE) were investigated. Voltage dependence of monochromatic cathodoluminescence (CL) was applied to investigate the threading dislocation (TD) behaviors. Fewer TDs were observed in CL images when the penetration depth of electron was made shorter by altering the acceleration voltage from 30 to 5kV. It was shown that many TDs were generated on the peaks of the cones, in-between cones, and in the coalescence regions, while there was almost no TD above the slopes of the cones. When the growth pressure was changed from 200 to 100Torr during the final stage, fewer TDs were observed in CL images, and the full widths at half maximum (FWHMs) for the (002) and (102) reflections’ X-ray diffraction (XRD) rocking curves decreased. Furthermore, when the growth temperature was decreased from 1040 to 1000°C during the middle stage, a clear hexagonal distribution of TDs was observed and the FWHMs for the (002) and (102) reflections’ XRD rocking curves further decreased. Atomic force microscopy (AFM) was used to investigate the surface morphology of the samples. In situ optical reflectivity spectra were measured to monitor the growth mode during the different growth stages. Based on the CL and reflectivity spectra results, the process of TDs’ evolution and distribution was deduced and sketched. [Copyright &y& Elsevier]

Abstract: The negative capacitance behavior in light-emitting diodes and laser diodes has been observed and characterized by using ac admittance–voltage method. Experimental results proved that the strong negative capacitance behavior is always accompanied by remarkable light emission. We confirmed that the negative capacitance is an effect of the junction instead of other behavior or measurement error. We presented a numerical calculation by solving one dimension continuity equation based on a simple diode model. The results show that the negative capacitance behavior in light-emitting diodes has great relation to injected carriers recombination in the active region of luminescence. [Copyright &y& Elsevier]

Abstract: The influence of the annealing pressure of the nucleation layer (NL) on the resistance of GaN films grown on sapphire by means of metal-organic chemical vapor deposition has been investigated. It is found that the sheet resistance of GaN increases significantly with decreasing the annealing pressure. When the annealing pressure is 10 kPa, GaN with sheet resistance higher than 1011 Ω/sq is achieved. It is determined that the edge-component threading dislocations (ETDs) rather than the screw-component ones are the dominant structural feature responsible for the resistance variation. Based on the analysis of in-situ reflectance and atomic force microscopy, it is believed that the island density and island size in the NL are the key factors accounting for the resistance variation in GaN. The high island density and small island size in the NL not only lead to more ETDs in GaN, which introduce more acceptors to compensate the background electrons, but also enhance the rapid coalescence in GaN and thus effectively limit the diffusion of oxygen impurities into GaN epilayers from GaN/sapphire interfaces. [Copyright &y& Elsevier]

InGaN/GaN layers have been grown under low pressure by metal-organic vapor phase epitaxy on sapphire substrate. X-ray diffraction (XRD), photoluminescence, and optical absorption measurements have been performed to study the radiative recombination mechanisms in the samples. The In composition was determined by XRD measurement using Vegard''s law. With increasing In composition, a red shift of absorption edge and a broad Urbach tail in absorption spectra were observed. The InN inclusions in InGaN played a key role in long-wavelength absorption. There existed large Stokes shifts in all thick InGaN layers with different In compositions. The intensities of low-energy emissions were enhanced compared to those of high-energy ones with increasing In composition. We attributed low-energy emissions to deep levels and high-energy emissions to In-rich quantum dots. [Copyright &y& Elsevier]

Plasma-induced damage of n-type GaN in Cl2/CH4/Ar reactants and its recovery by the O2/CHF3 plasma in a reactive ion etching (RIE) system were studied by photoluminescence and Hall measurements. The mobility and optical properties of n-type GaN etched in Cl2/CH4/Ar were degraded gradually with increased radio frequency power. The effects of O2/CHF3 plasma treatment on the electrical and optical properties of n-type etched GaN were investigated by changing the ratio of O2/CHF3 flow rate. It was found that the damage caused by the conventional RIE process could be partly recovered by O2/CHF3 plasma treatment. The recovery mechanism was also discussed. [Copyright &y& Elsevier]