Research On The Growth Mechanism Of GaN And In GaN Based On MBE

With the advent of the 5G era and the all-round improvement of the demand for lighting and display,the third-generation semiconductor represented by nitride and Si C have a full bloom.Nitride semiconductor materials,with their superior optoelectronic performance advantages,quickly gain a foothold in the current environment of rapid innovation and iteration of semiconductor technology.At the same time,with a series of civilian applications such as solid-state white light lighting,Micro-LED displays,and high-power power electronic devices,Nitride semiconductor materials have absolute right to speak in the above industry with great market prospects.At the same time,nitride semiconductor materials are also of far-reaching significance to national defense.Their wide application in solar-blind detection and visible light communication is worth investing a lot of manpower and material resources.However,the development of nitride semiconductors has always been restricted due to the difficulty in the epitaxial technology,especially high-quality and high-In content In Ga N,high-quality and high-Al content Al Ga N,p-type Al Ga N and other problems.Researchers related also focus on researching and solving these problems.In this background,this thesis is based on molecular beam epitaxy(MBE)technology,which focuses on the MBE epitaxy of nitride materials.This thesis studies the growth mechanism and growth mode of MBE's homoepitaxial Ga N;then explores the influence of growth parameters on the properties of MBE heteroepitaxial In Ga N films,and further masters the methods of adjusting the composition and other characteristics of In Ga N;finally,summarizes the growth process of MBE epitaxial In Ga N under In-rich conditions,which is based on the modification effect of metal droplets formed by In atom clusters on MBE heteroepitaxial In Ga N.Based on these,the research content and results of this thesis are as follows:(1)In the process of MBE homoepitaxial Ga N,when the Ga source is sufficient,it can be observed from RHEED that the desorption of Ga atoms due to temperature is generally divided into two stages: the desorption of the two Ga wetting layers and the rest desorption of Ga atoms.The Ga atom desorption time in the first stage becomes longer as the Ga beam flux increases and the substrate temperature decreases;the Ga atom desorption time in the second stage increases as the temperature decreases,but does not change with the Ga beam flux.Therefore,the two stages of Ga adsorption can be deduced: the adsorption of the two Ga wetting layers and the adsorption of the remaining Ga atoms.(2)MBE homoepitaxial Ga N usually has three growth modes,namely: nitrogenrich growth mode,slightly Ga rich growth mode and excessive Ga-rich(Ga droplets)growth mode.In the nitrogen-rich growth mode,there is no Ga droplets attached,the surface morphology is rough and porous,the yellow band of PL spectrum defects is obvious,and the crystal quality is poor;in the Ga droplets growth mode,the surface is densely packed with Ga droplets,and the surface morphology presents a twodimensional step in addition to hexagonal hillocks,the PL yellow band becomes weaker,and the crystal quality is improved;while the sample grown in the slightly Ga growth mode has no Ga droplets or a few Ga droplets on the surface,and the PL spectrum has the weakest yellow light at the same growth temperature,so the crystal quality is the best.In this growth mode,the surface roughness of the Ga N epitaxial layer can be as low as 0.28 nm,and the FWHM of the PL band edge peak at room temperature is 6.16 nm.(3)In MBE heteroepitaxial growth of In Ga N films,reducing the growth temperature and increasing the In beam current within a certain range can increase the incorporation efficiency of In atoms,thereby increasing the In composition of In Ga N.With the increase of the In composition,although the PL band edge peak is red-shifted,the band edge luminescence peak broadens and the crystal quality decreases.At the same time,the graininess and roughness of the In Ga N surface are enhanced to a certain extent.The growth time is also very important for the incorporation of In atoms.In the early stage of In Ga N thin film heteroepitaxial growth,the incorporation of In atoms is small.As the growth time goes on,the incorporation efficiency of In atoms will gradually increase.(4)In droplets play an important role in MBE heteroepitaxial In Ga N.On the one hand,growth conditions will affect the distribution and morphology of In droplets.The increase of the growth temperature will make the In droplets show a smooth and round appearance,while the In droplets will appear tailed under the condition of low growth temperature.At the same time,the density of In droplets distributed on the surface of In Ga N will increase with the increase of the In beam current and the decrease of the growth temperature.(5)On the other hand,the presence of In droplets will change the growth conditions near the droplets,making the In Ga N growth process in the area covered by the In droplets different from other areas,and the properties are also different from the area without In droplet coverage.Under the coverage of In droplets,In atoms are more likely to migrate to In droplet clusters instead of participating in the growth of the In Ga N,resulting in the growth rate and In composition below the area covered by In droplets being lower than other areas.