High quality AlN and GaN grown on compliant Si/SiC substrates by gas source molecular beam epitaxy

Epitaxial layers of AlN and GaN were grown by gas source molecular-beam epi taxy on a composite substrate consisting of a thin (250 nm) layer of silico n (Ill)bonded to a polycrystalline SiC substrate. Two dimensional growth mo des of AlN and GaN were observed. We show that the plastic deformation of t he thin Si layer results in initial relaxation of the AlN buffer layer and thus eliminates cracking of the epitaxial layer of GaN. Raman, x-ray diffra ction, and cathodoluminescence measurements confirm the wurtzite structure of the GaN epilayer and the c-axis crystal growth orientation. The average stress in the GaN layer is estimated at 320 MPa. This is a factor of two le ss than the stress reported for HVPE growth on 6H-SiC(0001).