Electrical Transport Properties of Undoped CVD Diamond Films

Polycrystalline diamond films synthesized by microwave-assisted chemical vapor deposition (MACVD) were examined with transient photoconductivity, and two fundamental electrical transport properties, the carrier mobility and lifetime, were measured. The highest mobility measured is 50 centimeters squared per volt per second at low initial carrier densities ( 15 per cubic centimeter). Electron-hole scattering causes the carrier mobility to decrease at higher carrier densities. Although not measured directly, the carrier lifetime was inferred to be 40 picoseconds. The average drift length of the carriers is smaller than the average grain size and appears to be limited by defects within the grains. The carrier mobility in the MACVD films is higher than values measured in lower quality dc-plasma films but is much smaller than that of single-crystal natural diamond.