Large area microwave-plasma CVD of diamond wafers for optical and thermal applications

Based on numerical simulations, a novel microwave-plasma CVD reactor with an elliptical cavity has been designed that exhibits excellent performance and stability. After the successful test of a system with 2.45 GHz and 6 kW microwave power, an up-scaled version equipped with a 915 MHz, 60 kW generator has been realized, which allows deposition on 6" substrates. These reactors have been utilized to deposit diamond layers of up to 1 mm thickness. CVD diamond wafers with thermal conductivity up to 20 W/cmK have been processed into heat spreaders to be used as submounts of high power laser diodes, thus providing improved cooling performance. The diamond windows exhibit broad-band optical transmission. Optical absorption coefficients at 10.6 mu m below 0. 1 cm(-1) have been measured, suggesting applications as windows for high-power C02 lasers.