Extraction of a Local Thermal Conductivity in CVD Diamond Films

Abstract

One might expect the columnar-grain microstructure of chemical-vapordeposited (CVD) diamond films to have a strong effect on the thermal conductivity κ. It was recently demonstrated [1] that the local conductivity κ_local at room temperature of high-quality microwave-plasma-deposited diamond indeed exhibits a strong gradient with respect to position in the films. κ_local was deduced by studying a series of films of different thickness prepared under as identical conditions as possible, the only parameter differentiating the samples being the time of deposition. The local conductivity at height z above the substrate was obtained as the derivative of the measured conductance Zicobs: Zκ_obs: κ_local(z) = d (Zκ_obs)/dZ, where the observed conductivity is necessarily averaged over the sample thickness Z by the nature of the measurement. The results, Fig. 1, show that κ_local increases by at least a factor of four going from the substrate surface to the top of a thick (~ 400 µm) sample. Here we present the results of such measurements over a wide temperature range, 6–400K, which allows us to extract the phonon scattering strengths as a function of position z within a sample.