Deposition and crystallization of amorphous GaN buffer layers on Si(111)substrates

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-ra y diffraction (XRD) and a high-resolution transmission electron microscope (HRTEM). The amorphous GaN layers were deposited by MOCVD at 300 degrees C. The islanding process by annealing at higher temperatures has been reveale d by AFM. It is found that the amorphous layers begin to be crystallized by solid-phase epitaxy at 500 degrees C in MOCVD, and the full-developed isla nds formed at about 600 degrees C. XRD data show that the GaN peak appeared only after an annealing at higher temperatures. Cross-sectional HRTEM micr ographs of the buffer region of the samples with amorphous GaN buffer layer s 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 h ave the same crystal orientation. The amorphous buffer layer deposited at 3 00 degrees C and the buffer layer directly deposited at 550 degrees C are u sed in the growth of GaN epilayers, respectively. The XRD results and photo luminescence at room temperature of such GaN epilayers show that using the amorphous GaN buffer layer lead to monocrystalline and a narrower full-widt h at half-maximum (FWHM) of near band emission (16 nm) than using the buffe r layer directly deposited at 550 degrees C (FWHM of 21 nm). These results indicate that the quality of GaN epilayer on Si(1 1 1) can be improved by u sing the amorphous GaN buffer layer. (C) 2000 Elsevier Science B.V. All rig hts reserved.