Papers by Author: Hiromu Shiomi

Abstract: The effects of basal-plane defects on the performance of 4H-SiC Schottky diodes using a Ni electrode are demonstrated. Systematic characterization was performed using 4H-SiC epitaxial layers grown by sublimation epitaxy on substrates with various off-axis angles. As the off-axis angle increases, the ideality factor of the current-voltage characteristics increases, and the Schottky barrier height decreases, corresponding to an increase in the number of basal-plane defects. The reverse-bias current degrades for high off-axis samples. These results indicate that basal-plane defects degrade the device performance. Schottky diodes that possesses good characteristics were obtained for samples with low off-axis angles (2o- and 4o-off samples).

Abstract: Thermal anisotropy in 4H-, and 6H-SiC bulk single crystal wafers was studied by the PPE method. The thermal diffusivities of the [1-100] and [11-20] orientations (^c-axis) samples were higher than those of the [0001] orientation (//c-axis) samples. Moreover, the thermal anisotropies of the lattice component and the carrier component were analyzed by Raman measurement.

Abstract: 4H-SiC was grown on 4H-SiC (1100) substrates by sublimation boule growth, and transmission electron microscopic investigation was carried out. Two basal-plane-dislocations in the same basal plane (the BPD pair), whose dislocation line extend toward the [1100] growth direction, were observed as aligned along [0001]. The density of the BPD pairs along [0001] was in the same order with that of the stacking faults in the sample. A threading screw-dislocation was observed in between aligned BPD pairs. It is proposed that the interaction between stacking faults and threading screw-dislocations on the grown surface generates the BPD pairs. Since a high density of stacking faults is inherent to the growth on the substrates perpendicular to (0001), keeping an atomically flat grown surface is important to prevent the generation of the threading screw-dislocations, and thus to suppress the generation of the BPD pairs in case of the growth on (1100) and/or (11 2 0) substrates.

Abstract: The advantage of room-temperature photoluminescence (PL) mapping was demonstrated for nondestructive detection of stacking faults (SFs) in off-oriented 4H-SiC epitaxial and bulk wafers. In mapping of the SF-related emission at 2.9 eV on the wafers, the SFs in the surface region appeared as a bar-shaped pattern with the long side perpendicular to the off-cut direction. The use of 266 nm light excitation is essential to detect the SF pattern in the bulk wafers because of its shallow penetration depth. The dark lines crossing the bar-shaped patterns in the epitaxial wafers are ascribable to the basal plane dislocation located close to the SF-planes.

Abstract: The effectiveness of room-temperature photoluminescence (PL) mapping was demonstrated for nondestructive detection of structural defects, such as dislocations, micropipes and stacking faults, in SiC wafers. PL spectra of bulk wafers were dominated by deep-level emissions due to Si vacancies, vanadium and undefined centers like UD-1 at room temperature, while those from epitaxial wafers involved near band-edge emission. We developed a whole-wafer PL intensity mapping system with a capability of zooming in on the area of interest with a spatial resolution as high as 1 μm, and showed that the mapping patterns agree well with the etch-pit patterns originating from the structural defects both on a wafer scale and on a microscopic scale. The intensity contrast around the defects varied depending on the emission band, suggesting differences in their interactions with impurities and point defects.

Abstract: We demonstrate high-speed and high-quality 6H-SiC homoepitaxial growth on a 1°-off c-plane SiC substrate by a closed-space sublimation method. By optimizing the size of single-crystal source materials in the growth system, a high-quality 6H-SiC epilayer with an X-ray diffraction rocking curve (0006) full-width at the half maximum (FWHM) of 38 arcsec was obtained. We also carried out doping of nitrogen and boron during the growth of the SiC epilayer. A strong donor-acceptor pair (DAP) emission at a peak wavelength of 570 nm under excitation by a 395 nm nitride-based light-emitting diode (LED) was observed. The 6H-SiC with DAP emission is promising for use as a phosphor in a nitride-based LED, because high-quality nitride layers can be grown on the SiC substrates with small off-oriented angles.

Abstract: Growth of 4H-SiC bulk crystals on 4H-SiC {03-38} seeds was done. 4H-SiC {03-38} is obtained by inclining the c-plane toward <01-10> at a 54.7 degrees angle. Growth on the 4H-SiC {03-38} seed has the potential to achieve high quality crystals without micropipes and stacking faults. Micropipe-free c-plane 4H-SiC wafers were achieved by growth on the 4H-SiC {03-38} seed. A transmission X-ray topograph image of the micropipe free c-plane wafer revealed that there are no macroscopic defects with displacements.