The Effect Of GaN Barrier Growth Atmosphere On Surface Morphology Evolution Behavior Of InGaN/GaN Multiple Quantum Well Structure

Gallium Nitride?GaN?,a wide-band gap semiconductor compound?E_g=3.4eV at 300 K?,is considered nowadays to be one of the most important semiconductor materials after Si.Over the past decades it has been widely used in the development of high brightness blue-green LEDs,short wavelength devices,solar cell,general illumination industry.Although the performance of these nitride-based LEDs had been very successful over the past decades,the progress of high quality LEDs was often limited by the fundamental problems associated with the growth of InGaN/GaN layers,and hence attracted much attention of related researchers.The InGaN/GaN multiple quantum wells?MQW?structures were grown on c-plane sapphire substrate by metal organic chemical vapor deposition?MOCVD?.1)InGaN/GaN MQW blue light emission samples with different hydrogen?H₂?percentage were obtained by varying the H₂ gas flow.The surface morphology evolution of the samples have been evaluated,as well as the photoelectric properties,and proposed physical mechanism.2)The effect of green emission MQWs with GaN barriers grown in the presence of a low ratio of H₂/N₂ mixture gas on surface morphology.And we have investigated the mechanism as well.The main results are as follows:Surface morphology evolution behavior of InGaN/GaN multiple quantum wells?MQWs?with different hydrogen?H₂?percentage during GaN barrier growth have been systematically studied.Ga surface-diffusion rate,stress relaxation and H₂ etching effect are found to be the main affecting factors of the surface evolution.As the percentage of H₂ increases from 0 to 6.25%,Ga surface-diffusion rate and the etch effect are gradually enhanced,which is beneficial to obtain a smooth surface with low pits density.As the H₂ proportion further increases,stress relaxation and H₂ over etching effect begin to be the dominant factors,which degrade the surface quality.Furthermore,the effects of surface evolution on the interface and optical properties of InGaN/GaN MQWs are also profoundly discussed.It is found that the introduction of moderate H₂could effective improve the interface quality and luminous efficiency.The comprehensive study on the surface evolution mechanisms herein provides both technical and theoretical support for the fabrication of high quality In GaN/GaN heterostructures.The effect of green emission MQWs with GaN barriers grown in the presence of a low ratio of H₂/N₂ mixture gas on surface morphology has been studied.It was found that surface morphology and interface quality can be greatly improved with the presence of H₂ for green emission MQWs.Contrary to blue emission MQWs,this improvement of green emission MQWs is mainly due to the enhanced 2-Dimensional?2D?growth by the elimination of inclusions.Systematically study has been made about the the formation mechanism of inclusion in green emission MQWs and its effect on surface morphology.After comparing with blue light emission MQWs,It can be easily noted that the enhancement of green emission MQW structure is much more obvious than that of blue one due to the low mobility of metal atoms in lower growth temperature,as confirmed by the huge improvement of surface and the luminescence efficiency.This study provides both technical and theoretical support,which is particularly important in the case of constructing high quality green LEDs.