PHOTOCONDUCTIVE SWITCH WITH CVD DIAMOND FILMS BY ULTRAVIOLET-LIGHT PULSE

Photoconductive properties of optical switch with CVD (Chemical Vapor Deposition) diamond film have been investigated. High resistivity of t he film and a new configuration of the diamond gap have made it possib le to avoid surface flashover and to apply static high electric field up to 2 x 10(6) V/cm. The mobility-carrier lifetime product (mu tau) w as increased to be linearly proportional to electric field for every g rain size sample, and no saturation was measured even at 3 X 10(5) V/c m. Larger grain size samples had larger mu tau value. The carrier life time was estimated from the fall time of the output waveform of the sw itch. Temporal response was 45 ps in 0.5 mu m grain size sample, which was reduced to 1/5 from that of natural diamond. It is also revealed that larger grain size samples had longer carrier lifetime. The grain size dependence is attributed to the decrease of the mobility and the lifetime inside the grain, and is not due to increasing recombination ratio at the grain boundary in smaller grain size samples.