THERMAL-CONDUCTIVITY OF CVD DIAMOND FILMS - HIGH-PRECISION, TEMPERATURE-RESOLVED MEASUREMENTS

We describe a high-precision measuring system for the determination of the in-plane thermal conductivity of CVD diamond samples al temperatu res between 77 and 900 K. The thermal conductivity is determined by es tablishing a well-defined steady-state heat flux through a diamond bar and by measuring the temperature gradient, using an array of eight th ermocouples. The heat is supplied by a meander-shaped microheater loca ted al one edge of the bar. By measuring the temperature distribution without heat production in the microheater, radiation losses are detec ted and corrected for. At room temperature the in-plane thermal conduc tivity of polished CVD diamond samples is determined with an accuracy better than 1%. A variety of CVD diamond samples deposited by microwav e plasma CVD under different growth conditions was investigated. Some of the samples showed extraordinarily high thermal conductivities of u p to 54 W cm(-1) K-1 at -150 degrees C. To our knowledge, this is the highest value reported so far for CVD diamond. The temperature depende nce of the thermal conductivity is well described by Callaway's theory . By fitting theoretical curves to the experimental values, informatio n about defect densities and grain boundaries is derived.