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Carrier lifetime in low carrier concentration 4H-SiC epitaxial layers grown on the C-face was enhanced by using carbon implantation and post annealing. The measured carrier lifetime increased with the thickness of the epitaxial layer and was 11.4 µs for the 150 µm thick epitaxial layer. The internal carrier lifetime was estimated as 21 µs from the dependence of the measured carrier lifetime on the epitaxial layer thickness. This value is almost comparable to the reported values of the internal carrier lifetime for the layers grown on the Si-face.

We investigated the potential of low off angled 4H-SiC epitaxial wafers for use in power device applications. To this end, we successfully grew epitaxial layers on 2 degree off-angled and vicinal 4H-SiC Si-face substrate with good surface morphology and low defects density. Schottky diodes, metal oxide semiconductor (MOS) capacitors, and trench metal oxide semiconductor field effective transistors (MOSFETs) were fabricated on these epitaxial layers, and we investigated their characteristics. The results were comparable, with respect to the Schottky diodes and trench MOSFETs and the reliability of MOS capacitors, to those for similar devices fabricated on 4 degree off-angled 4H-SiC Si-face epitaxial wafers. These results suggest that low off-angled 4H-SiC Si-face epitaxial wafers may be effectively utilized in power device applications.

The surface quality of epitaxial layers grown on 2° offcut substrates was improved. These substrates require a lower growth temperature and a lower C/Si ratio than their 4° offcut counterparts to suppress macro step bunching. Surface morphology, triangular defect density, and doping uniformity presented a trade-off relationship with respect to growth parameters. The implementation of a low C/Si ratio buffer layer led to a balance between surface defect density, which reached a minimum of 0.2 cm−2, and good doping uniformity on an equivalent wafer size (150 mm). An evaluation of metal–oxide–semiconductor capacitors and Schottky barrier diodes fabricated on 2° offcut epitaxial layers showed that the quality of these epitaxial layers was satisfactory for application in devices.

On 4H-SiC Si-face substrates after H2 etching, the defect with “line” feature parallel to a step as “bunched-step line” was observed. Using X-ray topography and KOH etching, we confirmed that the bunched-step line originated from basal plane dislocation (BPD). Use of the substrate with the lowest BPD density will be effective to reduce bunched-step line that would affect oxide layer reliability on an epitaxial layer. However, more detail investigation needs to classify the BPD that would become a starting point of bunched-step line.

The guidelines necessary to improve the n-type doping uniformity on C-face epitaxial growth of 4H-SiC have been examined as far as the practical throughput is maintained, e.g. 3×150 mm wafers with the growth rate higher than 20 μm/h. The flow-channel enlargement was carried out and the effect was estimated by temperature distribution estimation performed by hydrogen etching. Also, effective C/Si was simulated with the temperature distribution obtained from the hydrogen etching experiments. As a result, positional agreement was found between the region where carrier concentration begins to increase and the drastic drop in temperature and the effective C/Si ratio.

Homoepitaxial layers with different growth pit density were grown on 4H-SiC Si-face substrates by changing C/Si ratio, and the influence of the growth pit density on Schottky barrier diodes and metal-oxide-semiconductor capacitors were investigated. Even though there were many growth pits on the epi-layer, growth pit density did not affect the leakage current of Schottky barrier diodes and lifetime of constant current time dependent dielectric breakdown. By analyzing the growth pit shape, the aspect ratio of the growth pit was considered to be the key factor to the leakage current of the Schottky barrier diodes and the lifetime of metal-oxide-semiconductor capacitors.

A metal layer formed on the backside of InGaN/sapphire-based light-emitting diodes deteriorates the inherent optical power output. An experimental approach of a suspended die is employed to study the effects of such metal layers via a direct comparison in radiant flux from a discrete die with and without a reflector. A sphere package that employs no reflector is proposed and fabricated. Light extraction of the sphere design is discussed; a light source in the sphere package would not have to be either an ideal point or placed at the center of the sphere, due to a finite critical angle at the sphere/air interface.

Abstract: To understand formation and deterioration mechanisms of Ta/Ti ohmic contacts that were previously developed for p-GaN, the electrical properties of the Ta/Ti contacts, which were deposited on undoped GaN substrates and subsequently annealed in vacuum (where a slash (/) sign indicates the deposition sequence), were studied. The Ta/Ti contacts displayed good ohmic behavior after annealing at a temperature of 800C for 10 min in vacuum, although the undoped GaN substrates were used. However, deterioration of the present ohmic contacts was observed during room-temperature storage. These contact properties were similar to those observed in the Ta/Ti contacts prepared on p-GaN. Hall-effect measurements revealed that thin n-type conductive layers were found to form on surfaces of both the undoped GaN and p-GaN substrates after annealing at 800C in vacuum.

Reduction of background carrier concentration was investigated for 4H-SiC C-face epitaxial growth in order to realize ultrahigh-voltage power devices. The quantitative contribution of each epitaxial growth parameter was studied, and it has been found that the growth rate increase and the pressure decrease were more effective than the C/Si ratio. Optimizing the parameters has made it possible to achieve a background carrier concentration of 7.6 x 1013 cm[?]3 within the whole area of specular 3-in. wafers. In addition to the background carrier concentration reduction, it has been confirmed that small epitaxial film thickness variation, low surface defect density and carrier lifetime fulfill the requirements for the devices. Moreover, in-process propane annealing has been found effective in improving the carrier lifetime. As a result, the longest lifetime value to date of 1.6 us was obtained for a C-face epitaxial film.

We investigated the potential of low off angled 4H-SiC epitaxial wafers for use in power device applications. To this end, we successfully grew epitaxial layers on 2 degree off-angled and vicinal 4H-SiC Si-face substrate with good surface morphology and low defects density. Schottky diodes, metal oxide semiconductor (MOS) capacitors, and trench metal oxide semiconductor field effective transistors (MOSFETs) were fabricated on these epitaxial layers, and we investigated their characteristics. The results were comparable, with respect to the Schottky diodes and trench MOSFETs and the reliability of MOS capacitors, to those for similar devices fabricated on 4 degree off-angled 4H-SiC Si-face epitaxial wafers. These results suggest that low off-angled 4H-SiC Si-face epitaxial wafers may be effectively utilized in power device applications.

Quantization effects on optical polarization switching in (1122)-oriented InGaN/GaN quantum-well (QW) structures, which were not evident in the previous report by Ueda et al., have been firmly confirmed. The present study found that polarization ratios became more negative as the luminescence photon energy was decreased from 2.6 eV. Enhancement in optical polarization was found in thin QW structures, which is believed to be a result of quantization effects. Sample structures containing thick InGaN and AlGaN layers showed polarization ratios shifted towards positive values; these samples exhibited in-plane luminescence inhomogeneity with stripe morphologies parallel to [1100] and dark lines appearing at angles between 50 and 62° with respect to [1100].

Continuous-wave (CW) operations of semipolar (1 12 2) plane InGaN/GaN laser diodes (LDs) were demonstrated. The LD structures were grown on low extended defect density semipolar (1 12 2) GaN bulk substrates, using conventional metal organic chemical vapor deposition (MOCVD) at atmospheric pressure. The threshold current was 54 mA (6.5 kA/cm2) for the CW operation [39 mA (4.6 kA/cm2) for pulsed mode]. Stimulated emission was observed at 405.9 nm with a spectral line-width of 1 nm. These results indicate that semipolar (1 12 2) GaN is a promising orientation for the realization of blue-green and green LDs.

Semipolar (1122) plane III-nitride laser diodes (LDs) were realized on low extended defect density semipolar (1122) GaN bulk substrates. The LD structures were grown by conventional atmospheric-pressure metal organic chemical vapor deposition (MOCVD), using conditions similar to that of c-plane nitride device growth. The mirror facet for a laser cavity was formed by dry-etching of III-V nitride films without cleaving. Stimulated emission was observed at 426.9 nm with a full width at half maximum (FWHM) of less than 1 nm. The (1122) plane laser diode had threshold currents (Ith) of 306 mA, corresponding to a threshold current densities (Jth) of 12.8 kA/cm2.