Dynamic performance of UV photodetectors based on polycrystalline diamond

Dynamic behavior of photogenerated carriers in diamond-based UV photodetect ors is investigated over a wide excitation frequency range, enabling an ana lysis of the influence of film morphology and impurity content on device re sponse times. Under pulsed light excitation, short time detector photorespo nse varies from 2.5 to 10 ns, whereas carrier lifetimes estimated under ste ady-state illumination lie in the 0.1-1 ns range, exhibiting a small depend ence on the film microstructure. Conversely, very long response times, stro ngly dependent on film characteristics, are detected by decreasing the exci tation frequency. Such results are discussed in terms of carrier recombinat ion at defect- and impurity-related centers, trapping at localized states c lose to the band edges, and dispersive transport. It is suggested that devi ce response times are mainly related to charge trapping either into discret e or continuously distributed energy levels, rather than to recombination o f carriers at midgap defect states.