Effects of step-graded AlxGa1-xN interlayer on properties of GaN grown on Si(111) using ultrahigh vacuum chemical vapor deposition

We report the growth of high-quality GaN on a Si(111) substrate using a five step-graded AlxGa1-xN (x=0.87-0.07) interlayer between GaN epilayer and AlN buffer layer by ultrahigh vacuum chemical vapor deposition. The crack density and the surface roughness of the GaN layer grown on the graded AlxGa1-xN interlayer were substantially reduced, compared to those of GaN grown on an AlN buffer layer. Significant improvement in the structural and optical properties of the GaN layer was also achieved by the use of a graded interlayer. These results are attributed to the decrease of the lattice mismatch between GaN and AlN layer, and the reduction of the thermal stress by the graded interlayer. (C) 2001 American Institute of Physics.