Microstructural investigations on GaN films grwon by laser induced molecular beam epitaxy

摘要

Microstructural investigations on GaN films grown on SiC and sapphire substrates by laser induced molecular beam epitaxy have been performed. Threading dislocations with Burgers vectors of 1/3<1120>, 1/3<1123> and [0001] are typical line defects predominatly the first type of dislocations. Their densities are typically 1.5x10~(10) cm~(-2) and 4-10~9 cm~(-2) on SiC and sapphire, respectively. Additionally, planar defects characterized as inversion domain boundaries lying of {1100} planes have been observed in GaN/sapphire samples with an inversion domain density of 4x10~9 cm~(-2). The inversion domains are of Ga-polarity with respect to the N-plarity of the adjacent matrix. However, GaN layers grown on SiC show Ga-polarity. Possible reasons for the different morphologies and structures of the films growth on different substrates are discussed. Based on an analysis of displacement fringes of inversion domains, an atomic model of the IDB-II with Ga-N bonds across the boundary was deduced. High resolution transmission electron microscopy (HRTEM) observations and the corresponding simulations confirmed the IDB-II structure determined by the analysis of displacement fringes.