SIMPLE CORRELATION BETWEEN OPTICAL-ABSORPTION AND THERMAL-CONDUCTIVITY OF CVD DIAMOND

The relationship between the thermal conductivity and optical absorption was investigated for over 60 samples of CVD diamond grown in ten different laboratories. The thermal conductivities kappa(parallel to) and kappa(parallel to) (with heat flow parallel or perpendicular to the plane of the sample) were measured by steady state and laser flash techniques respectively. A simple and inexpensive apparatus is described to enable accurate and rapid measurement of the optical absorption coefficient alpha averaged over the visible spectrum. A clear correlation was found between kappa(parallel to) or kappa(perpendicular to) and alpha, which can be fitted using a particularly simple expression with coefficients for kappa(parallel to) vs. alpha which are slightly different from those for k(perpendicular to) vs. alpha. The behavior can be used to obtain estimates of kappa(parallel to) or kappa(perpendicular to) (within uncertainties of approximately +/-3 W cm(-1) K-1) from optical absorption measurements.