Chapter 10 - Structural defects in nitride heteroepitaxy

Abstract

GaN films must be grown heteroepitaxially on a variety of alternative substrates because of the difficulty in growing sufficiently large GaN substrates. Despite large differences in lattice parameters and thermal expansion coefficients, GaN thin films have been grown on c-plane sapphire, a-plane sapphire, and SiC. As a consequence of heteroepitaxy, the resulting film suffers from a large density of extended defects. The differences in lattice parameter and coefficient of thermal expansion lead to large dislocation densities, whereas, the differences in the surface and the interfacial energies often lead to the formation of islands and planar defects. Heteroepitaxial c-axis growth of a polar material like GaN also introduces the problem of inversion domain boundaries (IDBs) as well as the possibility that the deposited film may have one of two polarities: Ga-terminated or N-terminated. Extended defects in heteroepitaxial GaN films grown by MOVPE (metalorganic vapor phase epitaxy) scatter carriers result in lower mobility and surround themselves with point defects and impurities, which act to compensate the dopants.