The initiation of GaN growth by molecular beam epitaxy on GaN composite substrates

摘要

We report on an investigation of the initial stages of growth by molecular beam epitaxy (MBE) of GaN layers on composite substrates consisting of hydride vapor have epitaxial (HVPE) GaN films on SiC substrates. In situ reflection high energy electron diffraction (RHEED) and atomic force microscopy (AFM) were used to monitor the surface, reconstruction of the GaN and to measure he structure of the grown surface, respectively. A 1x3 streaky RHEED pattern was observed on the HVPE GaN layers from room temperatures up to 750 deg C. This corresponds to a (3x3) R 30deg reconstruction of the GaN surface. AWt a substrate temperature of 600-650 deg C, growth by MBE of GaN layers on the HOPE GaN substrate leads to a change of he RHEED pattern from 1x3 to hexagonal 2x2 during the first few minutes of epitaxy. RHEED oscillations were observed at the beginning of growth at 40-0 deg C. MBE growth at higher temperatures ￣730-750 deg C significantly enhances the flatness of the surface of the GaN layer. In this case, RHEED patterns were more intense and streaky8 than those seen for GaN layers grown at lower temperatures. The surface of the MBE GaN layers grown at high temperatures were atomically flat within the sensitivity of our AFM system.