Thermal conductivity of heavily doped bulk crystals GaN:O. Free carriers contribution

Abstract

Here we report the results of an experimental study of the thermal conductivity of GaN crystals doped by oxygen with concentrations of 4 × 1016, 2.6 × 1018 and 1.1 × 1020 cm−3, carried out in the temperature interval 7–318 K. We observed the highest thermal conductivity ever reported for GaN, 269 Wm–1 K–1 at 300 K, in the sample with the lowest oxygen content. This result is explained by the renormalization of GaN elastic constants, caused by the effect of spontaneous polarization. Results were analyzed using the Callaway model. The contribution of phonon scattering by free carriers in doped GaN crystals was considered for the first time. We show that free electrons reduce the thermal conductivity by up to 32%–42% at 300 K for a sample with a 1.1 × 1020 cm−3 of oxygen concentration.