Research On The Proterties Of InGaAs/GaAs Heterojunction Materials Grown By MOCVD

InxGa1-xAs/GaAs heterojunction materials has many advantages such as highabsorption coefficient, high mobility, good uniformity and stability comparing withconventional material and has wide applications in photoelectric devices. InGaAsdetectors with GaAs substrate possess shorter wavelength and have advantages infocal plane arrays. Therefore, there is considerable significance to get high qualityInGaAs/GaAs. High quality InGaAs/GaAs could not be easily got because of thelattice mismatch. Two-step growth was one of the most effective methods in solvingthe mismatch, just as its name implies, the buffer layer with different growthconditions is deposited first, after the anneal, epitaxial layer is grown subsequently.Buffer layer provide nucleation centers for epitaxial layer growth as a template andsuppress the dislocations, therefore epitaxial layer growth exhibits2-D growth modeand the quality of epitaxial layer was improved. In this paper, InGaAs was depositedon GaAs substrate through two-step growth by MOCVD for the first time. Effect ofbuffer layer thickness on quality of epitaxial layer has been studied, and the methodof two-step growth to reduce dislocation density was verified. The research providesa solid foundation for the following infrared detector.The heterostructure InGaAs/GaAs was investigated by scanning electronmicroscopy, atomic force microscopy, X-ray diffraction, Raman scattering spectroscopy, Electrochemical C-V Profiler and transmission electron microscopy.The effect of buffer layer thickness on epitaxial layer morphology, surface roughness,crystalline quality, alloy degree of order, the strain, intrinsic carrier concentrationand dislocation density was studied.SEM and AFM was adopted to investigate the effect of buffer layer thickness onsurface morphology and surface roughness. The results indicated that epitaxial layersurface morphology was improved when the buffer layer thickness exceeds a certainthickness, and the epitaxial layer surface morphology has no obvious changes whenthe buffer layer thickness continues to increase.XRD, Raman spectra and ECV was used to investigate the effect of buffer layerthickness on epitaxial layer quality, dislocation density, alloy degree of order, thestrain and carrier concentration. It was indicated that there exist an optimal bufferlayer thickness to get an epitaxial layer with excellent crystalline quality.The influence of buffer layer thickness on dislocation density and morphologyof epitaxial layer was studied. The results showed that dislocations distributerandomly in buffer layer and epitaxial layer. Certain thickness buffer layer waseffective in strain relaxation and suppression of dislocations. The faults anddislocations was restricted in interface to reduce the density. It is useless to suppressthe dislocations if buffer layer was too thin, then the dislocations will propagate tothe surface from buffer layer. Although thick buffer layer is effective for suppressionof dislocations, lots of dislocations will generate in the interface and upward to theepitaxial layer even to the surface. And the quality of epitaxial layer will decline.