No abstract

Step bunching on 6H–SiC (0001)-vicinal face etched by HCl at 1300–1500 °C is investigated by atomic force microscopy. When the substrate has the inclination toward near 〈011̄0〉 or even 〈112̄0〉, continuous parallel and periodic microsteps with six-bilayer height are laid perpendicular to the off direction, although those perpendicular to 〈112̄0〉 are apt to decompose into three bilayer or less. Formation mechanism of unit-cell-height steps is discussed based on consideration of bond configuration at step edges.

We succeeded in growing InN films two-dimensionally by radio-frequency plasma-excited molecular beam epitaxy (RF-MBE), using a low-temperature-grown InN buffer layer. From the results of reflection high-energy electron diffraction (RHEED) observation and X-ray diffraction (XRD) measurement, it was found that a single crystal of InN films with a wurtzite structure was obtained. Moreover, from the results of Hall effect measurement, it was found that the InN films had quite high electron mobilities. The best electron mobility at room temperature obtained in this study was 760 cm2/V·s and the corresponding carrier density was 3.0×1019 cm-3. To our knowledge, this electron mobility is the highest value ever reported for single crystal InN films.

We report epitaxial GaN layers grown on 6H-SiC (0001) substrates. A two stage substrate preparation procedure is described which effectively removes oxygen from the SiC substrate surface without the need of elaborate high temperature processing. In the first step, dangling Si bonds on the substrate surface are hydrogen passivated using a HF dip before introduction into vacuum. Second, the substrate is treated with a hydrogen plasma reducing the amount of oxygen-carbon bonding to below the x-ray photoemission detection limit. Upon heating in the molecular beam epitaxy (MBE) growth chamber, the SiC substrates are observed to have a sharp (1×1) reconstruction with Kikuchi lines readily visible. GaN epilayers deposited on AlN buffer layers by plasma enhanced MBE show sharp x-ray diffraction and photoluminescence peaks.

PACS: 78.55.Cr; 78.60.Hk; 78.66.Fd Optical characterization of In x Ga 1--x N layers was done by photoluminescence, cathodoluminescence and optical absorption measurements. PL emissions less than 1.9 eV were observed from In x Ga 1--x N films with x > 0.53 that showed no phase separation. A bowing parameter of 2.3 eV was obtained from the relationship between PL emission energy and alloy composition. Absorption edge dependence on In composition was similar to the luminescence peak dependence on In composition. These optical properties indicate that the bandgap energy of InN is below 1.0 eV.