Showing papers by "Tsunenobu Kimoto published in 1997"

Step-controlled epitaxial growth of SiC: High quality homoepitaxy

Abstract: Chemical vapor deposition (CVD) of silicon carbide (SiC) onto SiC{0001} substrates and its device applications are reviewed. Polytype-controlled epitaxial growth of SiC, which utilizes step-flow growth on off-oriented SiC{0001} substrates (step-controlled epitaxy), is proposed, and the detailed growth mechanism is discussed. In step-controlled epitaxy, SiC growth is controlled by the diffusion of reactants in a stagnant layer. Critical growth conditions where the growth mode changes from step-flow to two-dimensional nucleation are predicted as a function of growth conditions using a model describing SiC growth on vicinal {0001} substrates. Step bunching on the surfaces of SiC epilayers, nucleation, and step-dynamics are also investigated. The high quality of SiC epilayers was elucidated through low-temperature photoluminescence, Hall effect, and deep level measurements. Excellent doping controllability over a wide range was obtained by in situ doping of a nitrogen donor and aluminum/boron acceptors. Recent progress in SiC device fabrication using step-controlled epitaxial layers is presented. The intrinsic potential of SiC is demonstrated in the excellent performance of high-power, high-frequency, and high-temperature devices, which will develop novel electronics.

Deep Defect Centers in Silicon Carbide Monitored with Deep Level Transient Spectroscopy

Abstract: Electrical data obtained from deep level transient spectroscopy investigations on deep defect centers in the 3C, 4H, and 6H SiC polytypes are reviewed Emphasis is put on intrinsic defect centers observed in as-grown material and subsequent to ion implantation or electron irradiation as well as on defect centers caused by doping with or implantation of transition metals (vanadium, titanium, chromium, and scandium)

Step‐Controlled Epitaxial Growth of High‐Quality SiC Layers

Abstract: The growth mechanism in chemical vapor deposition (CVD) of silicon carbide (SiC) on off-oriented SiC{0001} substrates (step-controlled epitaxy) is reviewed. In step-controlled epitaxy, SiC growth is controlled by the diffusion of reactants in a stagnant layer. Critical growth conditions where the growth mode changes from step-flow to two-dimensional nucleation are predicted as a function of growth conditions using a model describing SiC growth on vicinal {0001} substrates. Step bunching on the surfaces of SiC epilayers is also investigated. Dominant step heights correspond to the half or full unit cell of SiC polytypes. The high quality of the SiC epilayers has been elucidated through Hall effect and deep level measurements. Excellent doping controllability in a wide range has been obtained by in-situ doping of a nitrogen donor and an aluminum acceptor.

Step bunching mechanism in chemical vapor deposition of 6H– and 4H–SiC{0001}

Abstract: Step bunching in chemical vapor deposition of 6H– and 4H–SiC on off-oriented {0001} faces is investigated with cross-sectional transmission electron microscopy. On an off-oriented (0001)Si face, three Si–C bilayer-height steps are the most dominant on 6H–SiC and four bilayer-height steps on 4H–SiC. In contrast, single bilayer-height steps show the highest probability on a (0001)C face for both 6H– and 4H–SiC epilayers grown with a C/Si ratio of 2.0. The increase of C/Si ratio up to 5.0 induces the formation of multiple-height steps even on a C face. The bunched step height corresponds to the unit cell or the half unit cell of SiC. The mechanism of step bunching is discussed with consideration of surface formation processes.

Nitrogen Ion Implantation into α-SiC Epitaxial Layers.

Abstract: N + implantation into p-type α-SiC (6H-SiC, 4H-SiC) epilayers at room and elevated temperatures, mainly obtained by the authors' group, has been reviewed. Since recrystallization of SiC is difficult, the implantation-induced damage should be minimal during implantation to achieve higher electrical activation. The effects of hot implantation are pronounced in high-dose (>10 15 cm -2 ) implantation. The lowest sheet resistance of 542 Ω/? was obtained by implantation at 500 to 800 °C with a 4 x 10 15 cm -2 dose. The properties of pn junctions formed by N + implantation into p-type epilayers are characterized in detail. The forward current is clearly divided into two components of diffusion and recombination currents. The diodes exhihited high breakdown voltages of 615 to 820 V, which are almost ideal values expected from device structure. The reverse leakage current can significantly be reduced by employing hot implantation at 800 °C.

Reduction of Double Positioning Twinning in 3C-SiC Grown on α-SiC Substrates

Abstract: Crystal growth of cubic silicon carbide (3C-SiC) on α-SiC (6H- and 15R-SiC) substrates was carried out by chemical vapor deposition. 3C-SiC (111) can be epitaxially grown on 6H- and 15R-SiC (0001) substrates. Due to the peculiar stacking sequence of α-SiC, double positioning boundaries (DPBs) appear in the 3C-SiC (111) layers. The layer on 15R-SiC has far fewer DPBs than that on 6H-SiC. Successive etching of a thick grown layer and successive observation of a growing surface revealed that the DPBs decreased anisotropically as crystal growth proceeded. Facets formed along DPBs were analyzed by atomic force microscopy. The angles between the facets and the grown surface (111) varied with the crystallographic orientation of DPBs. DPBs may decrease due to the lateral growth from the facets. The difference in the velocities of the anisotropic decrease in DPBs was discussed on the basis of the number of dangling bonds on the facets.

Deep Interface States in SiO 2/p-type α-SiC Structure

Abstract: Thermally grown SiO2/p-SiC interfaces were characterized by a high-frequency C-V measurement using a light illumination technique. A large negative flatband shift at room temperature in a p-type SiC MOS capacitor is caused by fixed charges in SiO2 near the interface and holes captured at deep interface states. The contribution of both components to the voltage shift could be separated by utilizing illumination. By illumination under the deep depletion condition, deep states emit holes and become neutral. Therefore, only fixed charges affect the voltage shift after the emission of holes from the deep states. From this method, the total deep state density was estimated to be 4~6 ×1012 cm-2 and the effective fixed charge density, 1 ~2 ×1011 cm-2, indicating that the flatband shift is mainly caused by holes trapped at deep interface states.

Photoluminescence of 3C-SiC Epilayers Grown on Lattice-Matched Substrates

Abstract: The photoluminescence (PL) spectra of 3C-SiC epilayers grown on 15R-SiC and on 3C-SiC were measured. The PL spectra show strong exciton-related peaks and weak impurity-related peaks. The epilayers are of high quality and have a low density of impurities. Peaks due to excitons bound to neutral nitrogen showed very little shift induced by strain. Peaks considered to be due to free exciton recombination were observed and analyzed. Defect-related bands, usually observed for 3C-SiC grown on Si, were not observed. Although weak defect-related peaks were still observed, the epilayers have a lower density of defects than those on Si.