Thickness dependent thermal conductivity of Zinc Selenide (ZnSe) – A combined Frequency Domain thermoreflectance and first principles study

Heat dissipation in nanostructures is critical as we reduce the system size in order to improve the system performance and reliability. In this study, we are reporting the length dependence thermal conductivity(k) of zinc-blende Zinc-Selenide (ZnSe) between 10 nm and 10000 nm. We measure the k of bulk Zinc-Selenide using Frequency Domain Thermoreflectance (FDTR) as well First principles calculations. This experimental method utilizes optical pump-probe technique which comprises of a pump laser, which is provides the heat to material under study and probe laser which measures the corresponding change in the temperature as function of the changing reflectivity of the material being heated by the continuous wave pump laser. The measurement is done by fitting the measured the phase lag, induced by the thermoreflective response of the material φ = φpump - φprobe to the phase lag that is measured using the 2D diffusion model, using various input parameters such as transducer thickness, thermal properties of the thin film metal transducer and the effective spot size of the probe beam that was measured during the experiment. Thermal conductivity of bulk ZnSe through FDTR measurement is 18 Wm^-1K^-1 which is in good agreement with the first principles calculations. Based on an agreement between FDTR and first principles computations, we are reporting the thickness (L=10 nm- 10000nm) dependent thermal conductivity of ZnSe. At nanometer length (L=100 nm), k of 7.08 Wm^-1K^-1 shows that ZnSe will be a candidate material for thermal interface materials.