Measurement of thermal conductivity of polycrystalline CVD diamond by laser-induced transient grating technique

The tangential thermal diffusivity D{sub ||} and thermal conductivity k{sub ||} of diamond plates grown from the gaseous phase by chemical vapour deposition (CVD diamond) are determined by the transient grating technique in the temperature range 25 - 200 {sup 0}C. Samples of insulating and boron-doped polycrystalline diamond of thickness about 0.3 mm and diameter 63 mm were synthesised in a microwave discharge in mixtures of methane and hydrogen. In view of the intense light scattering by the samples, a photosensitive grating recording technique was developed and used for measurements. It was found that the value k{sub ||} amounts to 18 - 20 W cm{sup -1} K{sup -1} at room temperature, approaching the thermal conductivity of the highest purity single crystals of diamond. A comparison of the value of k{sub ||} with the normal thermal conductivity k{sub perpendicular} determined by the flash method reveals a thermal conductivity anisotropy of about 10% - 20% associated with the texture of the diamond film, the normal component of thermal conductivity being larger than the tangential component. Boron-doped diamond displays a dependence of the transient grating kinetics on the excitation wavelength. The obtained results indicate that CVD diamond is a promising material for preparing efficient heat sinks, especially of large size, used in microelectronic devices and laser engineering. (laser applications and other topics in quantum electronics)