Selective growth of high quality GaN on Si(111) substrates

We demonstrate selective growth of high-quality GaN by gas-source molecular beam epitaxy on Si(111) wafers patterned with SiO2. GaN was grown on wafer s having two different buffer layers. The first buffer layer contains two A lGaN/GaN superlattices, separated by GaN spacer, grown on AlN, with a total thickness of 400 nm. The second is a thin AlN (1.5 nm) buffer layer. X-ray diffraction confirms (0001) growth orientation, smooth interfaces, and coh erence lengths comparable to the layer thickness in both samples. In the ca se of the thin AlN buffer layer, the tensile stress measured by the E-2 Ram an line shift is attributed to the mismatch in the thermal expansion coeffi cients of GaN and Si. However, when the AlGaN/GaN superlattice buffer layer is grown first, a reduced stress is measured. High carrier concentrations (approximate to 10(18) cm(-3)) are seen in the GaN grown on the thin AlN bu ffer layer, which we attribute to the incorporation of silicon from the sub strate during the growth process. The superlattice buffer layer is seen to inhibit this diffusion, resulting in a carrier concentration of < 10(17) cm (-3) in the GaN. (C) 2000 American Institute of Physics. [S0003-6951(00)012 14-6].