A study was made of the evolution of threading dislocations, stress and cracking of GaN films grown onto (111) Si substrates by using various buffer layers including thin AlN, compositionally graded AlxGa1-xN (0 ≤ x ≤ 1), and AlN/AlyGa1-yN/AlxGa1-xN (0 ≤ x ≤ 1, y = 0 and 0.25) multi-layer buffers. A reduction in threading dislocation density was found in GaN films grown onto graded AlxGa1-xN buffer layers, in comparison with those grown directly onto a thin AlN buffer layer. Threading dislocation bending and annihilation occurred in the region in the graded AlxGa1-xN grown under a compressive stress. This led to a decrease in threading dislocation density in the overgrown GaN films. In addition, growth of a thin AlN/AlyGa1-yN bilayer prior to growing a compositionally graded AlxGa1-xN buffer layer significantly reduced the initial threading dislocation density in the AlxGa1-xN buffer layer. This then further reduced the threading dislocation density in the overgrown GaN film. In situ stress measurements revealed a delayed compressive-to-tensile stress transition for GaN films grown onto graded AlxGa1-xN buffer layers or multi-layer buffers; in comparison to the film grown on a thin AlN buffer layer, which subsequently reduced crack densities in the films.

Evolution of Threading Dislocation Density and Stress in GaN Films Grown on (111) Si Substrates by Metalorganic Chemical Vapor Deposition. X.Weng, J.D.Acord, A.Jain, E.C.Dickey, J.M.Redwing: Journal of Electronic Materials, 2007, 36[4], 346-52