Study On The Luminescence Properties Of InGaN/GaN Thin Films And LED Under The Control Of Epitaxial Structure

Gallium nitride and its relevant alloy semiconductor materials are parts of the third-generation compound semiconductors for replacing the first?Si?Ge?and second?In P?Ga As?generations.Due to their superior optoelectronic properties,they have attracted widespread attentions in recent years.Among these ternary alloy materials,In_xGa_1-xN alloy has continuously adjustable bandgaps from 0.7 e V to 3.4 e V which covers the whole visible range.Therefore,it has great potentials in realizing full-color lighting,aerospace,medical,communication,luminescence,and so on.However,experiments have shown that when the In composition was greater than 20%,due to the lattice mismatch between the substrate and the epitaxial crystal,the piezoelectric field strength and internal strain of the material became high,and the dislocation density increased.This result leads to a low internal quantum efficiency of the active layers in GaN based devices composed of high In composition,which limits the development of LED devices with longer emission wavelength based on InGaN materials.To break through this bottleneck,the epitaxial structure of the corresponding LED device needs to be improved:for example,choose to replace the substrate seeking alternative substrates,or introducing quantum dot?QD?structure to release the internal stress existing in the thin film.During these processes,accurate thin-film microstructure characterizations and optical or optoelectronic performance analysis are necessary.Based on the above,in this work,a series of high-In composition InGaN/GaN heterogeneities thin film on Zn O and green light QD type InGaN LED were studied by multiple spectrum methods?high-resolution X-ray diffraction,X-ray photoelectron spectroscopy,Raman scattering spectroscopy,and time-resolved spectroscopy,etc.?,which has an important role in further guiding the growth of InGaN LED with high luminous efficiency through metal-organic chemical vapor deposition?MOCVD?technology.The main research contents are as follows:?1?A series of InGaN/GaN heterojunction films with high In composition was grown by MOCVD as research objects.By quantitative analysis using high-resolution X-ray diffraction,Rutherford backscattering spectroscopy and X-ray photoelectron spectroscopy,the In composition of InGaN/GaN heterojunction thin films were found as about 19%to 65%.The thickness of GaN buffer and InGaN layer are about 28 nm?57 nm and 52 nm?91 nm,respectively.Meanwhile,the crystal quality of InGaN epitaxial films with different components was analyzed by X-ray photoelectron spectroscopy,Rutherford backscatter spectroscopy,Raman scattering spectroscopy,and Photoluminescence spectroscopy.The results turned out that quality of InGaN/GaN/Zn O thin films with growth temperature in the range of 680??720?is better than other growth temperature.The above research shows that as the growth temperature increases,the diffusion of Zn and O atoms from the Zn O substrate to InGaN layer increases,which reduces the In composition and increases the interlayer compressive strain,resulting in the formation of impurity energy level.The above process is the root cause of the epitaxial thin film crystal quality degradation.?2?Based on the growth technology of MOCVD method,In-rich clusters are intentionally introduced into quantum wells,and the quasi-quantum dot structure is constructed by controlling the shape,size and In/Ga ratio,and these units were used as the research objects.Quantitative analysis using transmission electron microscopy and variable temperature steady-state photoluminescence spectroscopy showed that the average width of quantum dots and quantum wells were 2.4 nm and 4.5 nm,respectively.Furthermore,a more comprehensive carrier recombination dynamics model that integrates the exciton recombination model and the ABC recombination model was proposed to clarify the competition between radiated and non-radiated recombination of green light QD InGaN LED and various recombination paths relationship.Research based on the carrier recombination dynamics model shows that free carrier recombination occupies a dominant position at high temperature,low pulse injection,high energy state,and Schottky-Read-Hall non-radiative recombination?SRH?at a high defect density.Therefore,the free carrier recombination cannot be ignored,which further proves the necessity of proposing a new carrier recombination dynamic model.?3?Compared with the previously used method of relative internal quantum efficiency obtained by assuming that there is no non-radiative recombination at0 K,the new method based on the new model can be used to obtain the internal quantum efficiency more accurately and conveniently without any assumptions.And through analysis,the results show that there is a close relationship between the internal quantum efficiency and the concentration of injected carriers.Therefore,it is meaningful to discuss the internal quantum efficiency only if the carrier concentration is provided.