On the characteristics of AlGaN films grown on (111) and (001) Si substrates

High Al-content AlxGa1-xN films were deposited on (001) and (111) Si substrates at 1000°C using high temperature AlN buffer layers. Experimental results show that AlxGa1-xN films grown on (111) Si substrates exhibit better crystalline quality than that in the films deposited on (001) Si substrates. Cracks were found in the high Al-content AlxGa1-xN/(111) Si samples but they were not observed in the AlxGa1-xN films grown on (001) Si substrates having the same film thicknesses and Al compositions. Based upon the results of X-ray diffraction (XRD) and transmission electron microscopy (TEM), it appears that mono-crystalline AlxGa1-xN films were achieved on (111) Si substrates while columnar structure was observed in the AlxGa1-xN/(001) Si samples. According to the depth profiles of AlxGa1-xN/Si samples using secondary ion mass spectroscopic (SIMS) analyses, enhanced Al inter-diffusion in the Al xGa1-xN/(001) Si samples was identified. Room temperature (RT) photoluminescence (PL) measurements of the AlxGa1-xN (x≦0.10)/(111) Si samples exhibit strong near band edge luminescence. The PL emission linewidth was found to decrease with the decrement of Al-content.