Cross-plane temperature-dependent thermal conductivity of Al-doped zinc oxide thin films

We measured the cross-plane thermal conductivity of Al-doped zinc oxide (ZnO) with 0.5-1.5 at.% of Al. Al-doped ZnO thin films were prepared on SiO2/Si substrates by sol-gel spin coating. Thermal conductivity was measured at temperatures ranging from 20 to 300 K, using the four-point-probe 3-ω method. The measured thermal conductivity of the Al-doped ZnO thin films decreased as Al doping increasing up to 1.5 at.%. The average thermal conductivities of un-doped and Al-doped ZnO thin films were 1.1-5.6 W/m · K at 300 K. We suggest that this reduction of thermal conductivity with Al doping could reflect the combined effects of enhanced phonon scattering from grains and Al impurities, and the increasing porosity of the films with increasing Al doping. We also confirmed that the thermal conductivity of the films depends on Al doping.