Deposition and crystallization of amorphous GaN buffer layers on Si(1 1 1) substrates

Abstract

The deposition and crystallization of amorphous GaN buffer layers on Si(1 1 1) is firstly investigated by using an atomic force microscope (AFM), X-ray diffraction (XRD) and a high-resolution transmission electron microscope (HRTEM). The amorphous GaN layers were deposited by MOCVD at 300°C. The islanding process by annealing at higher temperatures has been revealed by AFM. It is found that the amorphous layers begin to be crystallized by solid-phase epitaxy at 500°C in MOCVD, and the full-developed islands formed at about 600°C. XRD data show that the GaN peak appeared only after an annealing at higher temperatures. Cross-sectional HRTEM micrographs of the buffer region of the samples with amorphous GaN buffer layers reveal that many domains exist in the GaN buffer layers and these domains misorientate each other with a small angle. The boundaries between domains locate near the bunched steps, and, the films on a terrace between steps have the same crystal orientation. The amorphous buffer layer deposited at 300°C and the buffer layer directly deposited at 550°C are used in the growth of GaN epilayers, respectively. The XRD results and photoluminescence at room temperature of such GaN epilayers show that using the amorphous GaN buffer layer lead to monocrystalline and a narrower full-width at half-maximum (FWHM) of near band emission (16 nm) than using the buffer layer directly deposited at 550°C (FWHM of 21 nm). These results indicate that the quality of GaN epilayer on Si(1 1 1) can be improved by using the amorphous GaN buffer layer.