Papers by Author: Fusao Hirose

Abstract: p-type SiC crystals doped with aluminum and nitrogen were grown by the sublimation method. We found that Al and N co-doping is effective for stabilized growth of p-type 4H-SiC polytype. We studied the relationship of polytype of grown crystals and the condition of Al and N feeding during the crystal growth. p-type 4H-SiC with p~1 x 10¹⁸ cm^-3 are stably-obtained with this method.

Abstract: The nitrogen (N) and aluminum (Al) co-doped growth of n-type 4H-SiC bulk crystals were performed by sublimation method. In the co-doping growth, we achieved the lowest resistivity of 6.9mWcm, and we also confirmed phenomenon of stacking faults suppression in spite of high N concentration more than 8 x 10¹⁹cm^-3.

Abstract: We have developed RAF (Repeated a-face) growth method which is high quality bulk crystal growth technology [1, 2]. A block crystal more than 150 mm square size was produced by the RAF growth method. Since c-face growth crystal was produced on the seed obtained from the block crystal, high quality 150mm 4H-SiC wafer was achieved. This paper reports the results of the quality evaluation.

Abstract: A reduction in threading screw dislocation (TSD) density in 4H-SiC (silicon carbide) crystal is required for SiC power devices. In this study, TSD’s transformation by the RAF (repeated a-face) growth method [1] is observed by transmission X-ray topography (g=0004) of the cross-section of the crystal. Increasing the number of repetitions of a-face growth and offsetting c-face growth to an angle of several degrees reduce TSDs. TSD density is reduced to 1.3 TSD/cm2. The RAF growth method is very effective towards growing high quality SiC crystals.

Abstract: Morphological features, such as the orientation and linearity of basal plane dislocations (BPDs) in SiC crystals, were analyzed by applying a two-dimensional fast Fourier transform (2D-FFT) to X-ray topographic images of the BPDs. An SiC crystal fabricated by an improved repeated a-face (RAF) method and an SiC crystal fabricated by an conventional RAF method discussed in a previous study were evaluated. In the 2D-FFT images of the improved crystal, streaks along the directions were observed, indicating that the BPDs were highly oriented along the directions. The degree of orientation of the BPDs, which may reflect their linearity, was calculated, and the improved RAF crystal had a much higher degree of orientation than the conventional RAF crystal.

Abstract: We investigated a way of reducing the stacking fault (SF) density on a highly nitrogen (N) doped 4H-SiC crystal. SFs were generated at highly N doped crystal exceeding 4 x 1019 cm-3 and the density was increased with increasing N concentration. We found that Al co-doping had the potential to suppress this SF generation and was effective up to an N concentration of about 1 x 1021cm-3. This effect depended strongly on the Al concentration. We discussed the reason for the SF suppression effect of Al co-doping.