A relatively large sample of gallium nitride (GaN) was grown as a single crystal using the hydride vapor phase epitaxy (HVPE) process. The thermal diffusivity of the single crystal has been measured using a vertical-type laser flash method. The thermal expansion was measured using a dilatometer in order to estimate the thermal diffusivity with sufficient reliability. The effect of sample thickness and temperature on thermal diffusivity was evaluated. The specific heat capacity of GaN was also measured by using a differential scanning calorimeter. The thermal properties of single-crystal GaN have been compared with the measured thermal properties of single-crystal silicon carbide (SiC). The thermal conductivity of single-crystal GaN at room temperature is found to be 253 AE 8:8% W/mK, which is approximately 60% of the value obtained for SiC. The excellent thermal property that is obtained in this study clearly indicates that GaN crystals are one of the promising materials for use in high-power-switching devices.
High-temperature powder X-ray diffraction measurements for ScAlMgO 4 (R 3m in space group) grown by Czochralski method were carried out from 303 to 1473 K. The obtained temperature-dependent unit cell parameters were expressed as L a ¼ 0:32489ð3Þ þ 1:78ð8Þ Â 10 À6 ðT À 273Þ þ 6:2ð6Þ Â 10 À10 ðT À 273Þ 2 for the a-axis and L c ¼ 2:5138ð2Þ þ 2:52ð5Þ Â 10 À5 ðT À 273Þ þ 5:6ð4Þ Â 10 À9 ðT À 273Þ 2 for the c-axis, where T is temperature in kelvin. The axial thermal expansion coefficients for the a-axis estimated from the unit cell parameters were comparable to those of GaN and ZnO. A c-plane ScAlMgO 4 substrate can be easily obtained with using cleavage plane along c-plane, which is parallel to a-axis. Thus, ScAlMgO 4 is one of the promising substrates for c-plane epitaxial growth of GaN and ZnO. High temperature X-ray single crystal structural analysis of ScAlMgO 4 demonstrated the mechanism of the nonlinear variation of the obtained cell parameters as a function of temperature.
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