S.Y. Xie

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-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.

Aluminum and GaN contacts on Si(111) and sapphire

Al and GaN contacts on both Si(111) and sapphire substrates were studied in this letter. After annealing at 450, 520, 600, and 650 °C for 35 min under a N2 flowing ambient, the current–voltage characteristics of Al/GaN contacts on Si(111) substrates were different from those on sapphire ones. The interfacial properties were discussed using the Schottky emission model in which the current is proportional to the square of the applied voltage. The metallurgical reactions were analyzed using photoluminescence (PL) spectra and x-ray diffraction (XRD). After annealing, blueshifts in the PL spectra and new peaks in the XRD data indicated that the wide-band gap interfacial phase AlGaN was formed at the Al/GaN interface.

Microstructures of AlGaN/AlN/Si (111) Grown by Metalorganic Chemical Vapor Deposition

In this paper the X-ray photoelectron spectrum and the Auger electron spectrum were used to study the microstructures of AlGaN/AlN/Si (111) grown by metal organic chemical vapor deposition. The results indicated that a broad transition region, about 20 nm, was present at the interface of AlN/Si and it was composed of AlN and SiN x (0 < x < 4/3). In AIN film the existence of Si-Si bonds was found. In the interface of AlGaN/AlN, the main incorporation form of N 1s varied gradually from AlN to the compound of GaN and AlN The diffusion of Si atoms was so strong at the high growth temperatures that the signal of Si 2p could be found throughout the epilayer.

Microstructures of GaN Buffer Layers Grown on Si(111) Using Rapic Thermal Process Low-Pressure Metalorganic Chemical Vapor Deposition

Microstructures of GaN buffer layers grown on Si (111) substrates using rapid thermal process low-pressure metalorganic chemical vapor deposition are investigated by an atomic force microscope (AFM) and a high-resolution transmission electron microscope (HRTEM). AFM images show that the islands appear in the GaN buffer layer after annealing at high temperature. Cross-sectional HRTEM micrographs of the buffer region of these samples indicate that there are bunched steps on the surface of the Si substrate and a lot of domains in GaN misorienting each other with small angles. The boundaries of those domains locate near the bunched steps, and the regions of the film on a terrace between steps have the same crystal orientation. An amorphous-like layer, about 3 nm thick, can also be observed between the GaN buffer layer and the Si substrate.

The oxidation of GaN epilayers in dry oxygen

The oxidation characteristics of GaN epilayers in dry oxygen have been studied. Bulk /spl theta/-2/spl theta/ X-ray diffraction (XRD) data showed that GaN began to be oxidized at 800/spl deg/C for 6 h. The oxide was identified as monoclinic /spl beta/-Ga/sub 2/O/sub 3/. The oxide layers were observed by a scanning electron microscope, which showed a rough oxide surface and an expansion of the volume of 40%. There is a rapid oxidation process in the initial stage of oxidation, followed by a relatively slow process when the temperature was over 1000/spl deg/C. The two-stage oxidation is limited by an interfacial reaction mechanism and a diffusion mechanism, respectively. The photoluminescence (PL) is seriously influenced by the oxidation.

Chemical structures of AlGaN/AlN/Si [111] by MOCVD using AES and XPS

In this paper X-ray photoelectron spectrum and Auger electron spectrum were used to study the microstructure of AlGaN/AlN/Si [111] grown by metal organic chemical vapor deposition. The results indicated that a broad transition region, composed of AlN, Si/sub 3/N/sub 4/, SiN/sub x/ (x<4/3) and Si was present at the interface of AlN/Si. At the interface of AlGaN/AlN, the main incorporation of N shifted from AlN to the compound of GaN and AlN gradually. The diffusion of Si atoms was very strong at the high growth temperatures and the signal of Si could be found in whole epilayers.