Intrinsic photoconductivity in polycrystalline CVD diamond films and in natural and synthetic bulk diamonds

Samples of natural and synthetic bulk diamonds were intrinsically excited using both ultraviolet laser pulses and pulses of synchrotron X-rays. The samples included microwave plasma-enhanced CVD polycrystalline diamond films and both natural type IIa and synthetic bulk diamonds. The diamonds produced by high-pressure synthesis, which have a low impurity content, are found to have much longer carrier lifetimes (greater than 10 ns) than the films (50 ps) and type IIa samples (100-500 ps). The longer carrier lifetimes in the bulk of synthetic diamonds permit carrier diffusion to the surface, and surface recombination becomes significant.