Analysis of GaN Grown on Vertically Standing Fractal-Like Si Nanostructures

Q.X. Wee, C.B. Soh, K.Y. Zang, S.J. Chua, C.V. Thompson
National University of Singapore (NUS), SG

Keywords: GaN, silicon, MOCVD, metal-assisted etching, strain, relaxation, nanostructures


We have investigated the microstructure and optical properties of GaN grown on vertically standing Si nanostructures by MOCVD. The Si nanostructures array is formed by a simple metal-assisted etching of Si(111) substrates, where both metal deposition and silicon etching occur simultaneously in one step, using HF and AgNO₃. It is found that continuous GaN film was formed on shorter Si nanostructures (<300nm), while discontinuous GaN was formed on longer Si nanostructures (~600nm). It should be noted that III-nitride material completely filled in between the gaps of silicon nanostructures for continuous film, while air gap is still present for discontinuous film. Despite having this morphological difference, XRD measurements suggest that both continuous and discontinuous GaN film are relaxed. However, the omega scan of both continuous and discontinuous film have a larger FWHM (49.9 arc-min and 93.4 arc-min, respectively) than GaN grown on flat Si (28.1 arc-min). This suggests that the nanostructures induced crystal misorientation in the GaN grown. A blueshift of the band-edge emission in photoluminescence also indicated that GaN grown on nanostructures are more relaxed than GaN on flat Si. Our research concluded that tensile strain in GaN is reduced by the nanostructures array, but crystal misorientation is resulted.