Epitaxial Growth of GaN on Si Substrate by Low Pressure Metal-Organic Chemical Vapor Deposition
In this thesis, the heterostructure growth of GaN on Si substrate by Low-pressure metal-organic chemical vapor deposition (LP-MOCVD) is studied. The investigation focuses on the growth of GaN on 6 “ Si (111) wafer. There different approaches werw including in this study. In the first approach, high quality GaN film was successfully grown on 150 mm Si (111) substrate by MOCVD method using multilayer AlN combined with the graded AlGaN layer as buffer. The buffer layer structure, film quality and film thickness are critical for the growth of the crack free GaN film on Si (111) substrate. Using multilayer AlN films grown at different temperatures combined with graded Al1-xGaxN film as the buffer, the tensile stress on the buffer layer was reduced and the compressive stress on the GaN film was increased, as a result, high quality 0.5 μm crack-free GaN epitaxial layer was successful grown on 6” Si substrate. In the second aaproach, the GaN film was grown on Si substrate using multilayer AlN/AlxGa1-xN buffer by low pressure metal organic chemical vapor deposition (MOCVD) method. The AlxGa1-xN films with Al composition varying from 0~ 0.66 was used to accommodate the stress induced between GaN and Si substrate during GaN growth. The correlation of the Al composition in the AlxGa1-xN films with respect to the stress induced in the GaN film grown was studied using high resolution X-ray diffraction including symmetrical and asymmetrical ω/2θ scans and reciprocal space maps. It is found that with proper design of the Al composition in the AlxGa1-xN buffer layer, crack-free GaN film can be successfully grown on 6” Si (111) substrates using multilayer AlN and AlxGa1-xN buffer layers Finally, in the third approach, low stress, low defect density GaN film was successful grown on circle array patterned Si (111) substrate using AlN as the nucleation buffer followed by two steps growth of the GaN film. Raman measurement shows a reduction of the in plane biaxial stress for the GaN film grown on patterned substrate. The slight blueshift of the band edge PL peaks further provides the evidence that the tensile stress in the GaN film was relaxed in the patterned Si substrate. It’s believed that the grain boundaries of the polycrystalline AlN buffer layer and the dislocations in the GaN film grown helped to relieve the stress induced by the lattice and the thermal coefficient mismatches during growth.
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