We have studied the evolution of threading dislocations (TDs), stress, and cracking of GaN films grown on (111) Si substrates using a variety of buffer layers including thin AlN, compositionally graded Al x Ga 1-x N (0 ≤ x ≤ 1), and AlN/Al y Ga 1-y N/Al x Ga 1-x N (0 ≤ x ≤ 1, y = 0 and 0.25) multilayer buffers. We find a reduction in TD density in GaN films grown on graded Al x Ga 1-x N buffer layers, in comparison with those grown directly on a thin AlN buffer layer. Threading dislocation bending and annihilation occurs in the region in the graded Al x Ga 1-x N grown under a compressive stress, which leads to a decrease of TD density in the overgrown GaN films. In addition, growing a thin AlN/Al y Ga 1-y N bilayer prior to growing the compositionally graded Al x Ga 1-x N buffer layer significantly reduces the initial TD density in the Al x Ga 1-x N buffer layer, which subsequently further reduces the TD density in the overgrown GaN film. In-situ stress measurements reveal a delayed compressive-to-tensile stress transition for GaN films grown on graded Al x Ga 1-x N buffer layers or multilayer buffers, in comparison to the film grown on a thin AlN buffer layer, which subsequently reduces the crack densities in the films.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Electrical and Electronic Engineering
- Materials Chemistry