Study On High-quality Non-polar A-plane GaN Heteroepitaxial

In recent years,the applications of ?-nitride-based power and optoelectronic devices are increasing due to their excellent performances.Up to now,most commercially available ?-nitride-based devices are grown on a c-plane GaN surface.However,the strong internal electrical field caused by the spontaneous and piezoelectric polarizations in c-plane GaN hinders the further improvement in the ?-nitride-based devices.A feasible approach is to grow GaN along a non-polar direction,which is free of polarization,including the?1120?a-and?10-10?m-directions.Heteroepitaxial growth is essential for mass production due to the high cost and limited size of non-polar GaN substrates.Moreover,a-plane GaN grown on r-plane sapphire has been considered as one of the promising solutions.Unfortunately,at present,there are two main problems in a-plane GaN grown on r-plane sapphire substrate:one is the high density of basal plane stacking faults and threading dislocations,and the other is in-plane anisotropy?anisotropy of crystal quality and anisotropy of surface morphology?.In an attempt to solve the above problems,in this paper,on the one hand the growth and characteristics of non-polar a-plane GaN directly grown on an Si O₂ stripe-patterned r-plane sapphire substrate were studied;on the other hand we demonstrate that a low-temperature GaN insertion layer could significantly improve the surface morphology of non-polar a-plane GaN.The main research contents and experimental results are as follows:1. The effects of the stripe-patterned r-plane sapphire substrate along the[0001]direction of GaN and the stripe-patterned substrate along the[1-100]direction on the crystal quality of non-polar a-plane GaN were systematically studied.When the stripes are parallel to[0001]direction,the dislocation density of the a-plane GaN decreases significantly,and when the stripes are parallel to[1-100]direction,the stacking faults density of the a-plane GaN decreases significantly.Besides,the effects of the two stripe-patterned substrates on the surface morphology of a-plane GaN are also compared.2. The effect of 3D layer growth time on non-polar a-plane GaN directly grownon an Si O₂ stripe-patterned r-plane sapphire substrate along the[0001]direction of GaN has been studied.The XRC-FWHMs values of the optimized a-plane GaN are 386arcsec along the c-axis and 289 arcsec along the m-axis.These values are one of the best results for a-plane GaN grown on r-plane sapphire so far,demonstrating significant improvement in crystal quality.Detailed scanning electron microscopy?SEM?,X-ray diffraction?XRD?reciprocal space maps?RSMs?,Williamson–Hall?W-H?analysis and Raman scattering studies are performed to investigate the growth kinetics.This work shows a very promising and simple method to achieve high-quality a-plane GaN films.3. The effects of low-temperature GaN insertion layer on the surfacemorphology of non-polar a-plane GaN were explored.Growth temperature and growth time of the GaN insertion layer are the two key factors in improving the surface morphology of a-plane GaN.The root-mean-square roughness of a-plane GaN is reduced by 75%compared to the sample without the GaN insertion layer.Meanwhile,the GaN insertion layer is also beneficial for improving crystal quality.This work provides a simple and effective method to improve the surface morphology of non-polar a-plane GaN.