Effects of the V/III Ratio of a Low-Temperature GaN Buffer Layer on the Structural and Optical Properties of a-GaN Films Grown on r-Plane Sapphire Substrates by MOCVD

We investigate the effects of the V/III ratio of a low-temperature GaN buffer layer on the growth of the overlaying nonpolar-plane GaN film grown on-plane sapphire by metal-organic chemical-vapor deposition(MOCVD).With other experimental conditions keeping fixed,the low-temperature GaN buffer layers are grown under various V/III ratios of 1000,3000,6000 and 9000,respectively.The characteristics of the-plane GaN films are analyzed by scanning electron microscopy,high resolution x-ray diffraction,Raman spectrum,and low temperature photoluminescence.The results show that the V/III ratio of the buffer layer has significant effects on the crystal quality of the a-plane GaN film,and a V/III ratio of 6000 is found to be the most suitable condition to achieve pit-free flat GaN surface.

Properties of Si Doped Al_(0.4)Ga_(0.6)N Epilayers with Different AlGaN Window Layer Grown on High Quality A1N Buffer by MOCVD

Si-doped Al_(0.4)Ga_(0.6)N(Si-Al_(0.4)Ga_(0.6)GN)epilayers grown on an AlGaN window layer(WL)with different Al contents are prepared using a high-quality A1N buffer layer by metal-organic chemical vapor deposition.Surface morphology,crystalline quality and electric properties of these epilayers are investigated by using atomic force microscopy,x-ray diffraction,Raman scattering spectrum and Hall techniques.Results show that the surface morphology of these epilayers are mainly determined by the Si-doping level which,together with the effect of Al content of WL,also has an obvious impact on the electron concentrations.On the other hand,the insertion of AlGaN WL is helpful to the increase of Si doping level and conductivity of subsequently grown Si-Al_(0.4)Ga_(0.6)N epilayers.However,the insertion as well as the increase of Al content of WL result in increase of dislocation densities,compressive strain in Si-Al_(0.4)Ga_(0.6)N epilayers,and tilt of A1N subgrains at the top interface of the buffer layer.Further,the degradation of crystalline quality with the Al content of WL exerts a decisive influence on the conductivity of the Si-Al_(0.4)Ga_(0.6)N epilayers grown on WL with Al content of 0.6 through a dramatic decrease in electron mobility.