Application of a time-resolved four-wave mixing technique for the determination of thermal properties of 4H–SiC crystals

Abstract

We applied a time-resolved four-wave mixing technique for the determination of thermal diffusivity, sound velocity, thermo-optic and photoelastic coefficients in heavily doped n-type and p-type 4H–SiC substrates. Spatial modulation of thermal properties was achieved by intraband carrier excitation using a light-interference pattern at 1064 nm and subsequent carrier thermalization. Decay of the light-induced thermal grating at its various periods and sample temperatures was monitored by diffraction of a delayed probe pulse at 532 nm wavelength. The grating decay kinetics provided the thermal diffusivity DT = 0.94 cm2 s−1, thermo-optic coefficient dn/dT = 3.6 × 10−5 K−1 and effective photoelastic constant at 300 K. Temperature dependences of dn/dT and thermal expansion almost matched that of the heat capacity, Cp(T), and correlated well with the Eg(T) dependence.