Heat capacity and phonon mean free path of wurtzite GaN

The authors report lattice specific heat of bulk hexagonal GaN measured by the heat flow method in the temperature range of $20–300\mathrm{K}$ and by the adiabatic method in the range of $5–70\mathrm{K}$ . The best fit with the accuracy of 3% was obtained for the temperature-independent Debye temperature ${\Theta }_D=365\mathrm{K}$ and Einstein temperature ${\Theta }_E=880\mathrm{K}$ . The authors relate these temperatures to the function of density of states. Using their results for heat conduction coefficient, they established in the temperature range of $10–100\mathrm{K}$ the explicit dependence of the phonon mean free path on temperature ${\ell }_{\mathrm{ph}}\propto T^{-2}$ . Above $100\mathrm{K}$ , there is an evidence of contribution of the Umklapp processes, which limits phonon free path at high temperatures.