Dynamic performance of UV photodetectors based on polycrystalline diamond

Dynamic behavior of photogenerated carriers in diamond-based UV photodetectors is investigated over a wide excitation frequency range, enabling an analysis of the influence of film morphology and impurity content on device response times. Under pulsed light excitation, short time detector photoresponse varies from 2.5 to 10 ns, whereas carrier lifetimes estimated under steady-state illumination lie in the 0.1-1 ns range, exhibiting a small dependence on the film microstructure. Conversely, very long response times, strongly dependent on film characteristics, are detected by decreasing the excitation frequency. Such results are discussed in terms of carrier recombination at defect- and impurity-related centers, trapping at localized states close to the band edges, and dispersive transport. It is suggested that device response times are mainly related to charge trapping either into discrete or continuously distributed energy levels, rather than to recombination of carriers at midgap defect states.