Porous silicon as an intermediate buffer layer for GaN growth on (100) Si

We report preliminary results on the growth of GaN on (100) Si substrate using porous silicon (PS) as an intermediate buffer layer. The growth was in situ monitored by laser beam reflectivity. Analysis of the evolution of the reflectivity signal indicates a change from relatively flat surface to rough one as the growth temperature (T_g) is increased. At a temperature of about 1050°C, the growth rate is very low and the reflected signal intensity is constant. When the growth temperature is varied, no drastic change of the porosity of the intermediate layer was detected. Scanning electron microscope (SEM) observations of the GaN/SP/Si structure revealed a good surface coverage at 500°C. When T_g increases, the structure morphology changes to columnar like structure at 600°C, and well-developed little crystallites with no preferential orientation appear at 800°C. These observations agree well with the X-ray diffraction (XRD) analysis. A preferential hexagonal growth is obtained at low growth temperature, while cubic phase begin to appear at elevated temperatures.