Research On Dislocation's Formation,Evolution And Inhibition In In_xGa_1-xAs Films Grown In Mismatch System

The ternary compound In_xGa_1-xAs,as a second-generation semiconductor material,becomes one of the basic materials of photoelectronic and electronic devices owing to its excellent optical and electrical properties.In_xGa_1-xAs has high stability,well-controlled large-area uniformity,high optical absorption coefficient,and large migration rate.In_xGa_1-xAs can be generated from two materials InAs and GaAs at any ratio.The lattice constant and band gap change in an approximately linear way with the variation of In.Especially,In_0.53Ga_0.47As that matches with the lattice constant of the InP substrate has verified In_xGa_1-xAs is one preferred infrared detector material at near-infrared band 0.9-1.7?m.In recent years,however,the demand for high-In In_xGa_1-xAs detectors is gradually intensified in the fields of space imaging?including earth remote sensing,atmospheric exploration,environmental monitoring?and spectroscopy,particularly the In_0.82Ga_0.18As infrared detecting devices with the cutoff wavelength 2.6?m?corresponding to In ratio of0.82?.Since the lattice constant of high-In In_0.82Ga_0.18As is 0.5986 nm,neither InP nor GaAs could well match with its crystal lattices,which leads to lattice mismatch during epitaxial growth.Moreover,the lattice mismatch would increase the dislocation and defect densities of epitaxial materials,thereby weakening the performances of devices.Thus,how to prepare high-quality In_xGa_1-xAs becomes one key technical issue to be solved.So far,the most commonly-used method is to introduce a buffer layer in between the epitaxial layer and the substrate,so as to address the lattice mismatch,which has brought about some achievements.Nevertheless,there is no substantial research or breakthrough concerning the interface problem,defect problem and mismatch dislocation of heteroepitaxial growth,the principle of the buffer layer inhibiting mismatch dislocations,or the proliferation of dislocation movement.In this study,from the perspective of microstructure microscopic analysis and using high-resolution transmission electron microscopy?TEM?,we studied the lattice mismatch of heterogrowth materials induced by the variation of In components.The forming mechanism of dislocations and the distributive laws of defects at the interface and epitaxial layer were clarified by analyzing the interface and defects in the epitaxial growth of In_xGa_1-xAs at the mismatch status.By optimizing the growth parameters and the buffer layer structure,we studied how to control the defects in mismatched heterogeneous structural materials.The findings theoretically and scientifically underlie the production of high-quality heteroepitaxial materials.Firstly,rules about the interfacial distribution of mismatch dislocation were clarified through tests with the In_xGa_1-xAs/InP mismatch system.Rules about the periodical arrangement in the dislocation aggregation zone were validated by computing the lattice constants of the mismatch materials at the two interfacial ends.The minimum length and the corresponding count of crystal cells in the mismatch dislocation aggregation zone on the interface were calculated at different degrees of mismatch.Then effects of positive and negative mismatch on the interfacial dislocation were studied.A new dislocation generation?origin?model was built by introducing dislocation and validated using the In_0.82Ga_0.18As extending layers at different growing temperatures and through the similar growth mismatch.Secondly,on basis of a film 2D-3D growth model,by combining dislocation movement and surface morphology,the relationships of dislocation movement with surface morphology and film quality were modeled.We thought the movement of mismatch dislocation was released at the surface of the epitaxial layer,and the dislocation aggregated at the surface of the epitaxial layer,leading to the surface roughness fluctuation at the epitaxial layer.Thus,the quality of the epitaxial films of In_xGa_1-xAs can be determined from the surface roughness.Thirdly,the addition of the buffer layer largely improved the quality of the epitaxial layer.We analyze the dislocation distributive laws at the interface and on surfaces.Moreover,the mechanism of buffer layer is explained by the proposed interface disorder model.Fourthly,the wettability between molten metal In and GaAs substrate was studied by means of high temperature and high vacuum wettability test system and extrusion drop method.The interfacial reaction between molten metal in and GaAs substrate was clarified,and the wettability between molten metal in and GaAs substrate was obtained.The formation mechanism of In_xGa_1-xAs on GaAs surface is also discussed.Fifth,a new method to prepare In_xGa_1-xAs buffer layer on GaAs substrates is proposed.In_xGa_1-xAs epitaxial layer was grown on the nano-In_xGa_1-xAs film as buffer layer,and the In_xGa_1-xAs epitaxial layer with good quality was obtained.