Thermal conductivity of Sc_xAl_1-xN and Y_xAl_1-xN alloys

Owing to their very large piezoelectric coefficients and spontaneous polarizations, (Sc,Y) xAl(1-x)N alloys have emerged as a new class of III-nitride semiconductor materials with great potential for high-frequency electronic and acoustic devices. The thermal conductivity of constituent materials is a key parameter for design, optimization, and thermal management of such devices. In this study, transient thermoreflectance technique is applied to measure the thermal conductivity of ScxAl1-xN and YxAl1-xN (0 = x = 0.22) layers grown by magnetron sputter epitaxy in the temperature range of 100-400 K. The room-temperature thermal conductivity of both alloys is found to decrease significantly with increasing Sc(Y) composition compared to that of AlN. We also found that the thermal conductivity of YxAl1-xN is lower than that of ScxAl1-xN for all studied compositions. In both alloys, the thermal conductivity increases with the temperature up to 250 K and then saturates. The experimental data are analyzed using a model based on the solution of the phonon Boltzmann transport equation within the relaxation time approximation. The contributions of different phonon-scattering mechanisms to the lattice thermal conductivity of (Sc,Y) xAl(1-x)N alloys are identified and discussed.