Time response analysis of ZnSe-based Schottky barrier photodetectors

We report on the characterization of ZnSe- and ZnMgBeSe-based Schottky barrier photodetectors grown on semi-insulating GaAs(001) by molecular-beam epitaxy. The spectral response of the devices shows a very sharp cutoff at variable wavelength, determined by the alloy composition, with a large stop-band rejection. Short-wavelength responsivities of 0.10 A/W and detectivities as high as 1.4×1012 cm Hz1/2 W−1 at −3.5 V bias have been achieved. Their time response behavior has been analyzed in detail. When light is switched off, the devices show photocurrent decays in the microsecond range, consisting of two exponential components with very different time constants. The slower component becomes dominant for high load and reverse bias. This behavior is related to the strong frequency dependence of the device capacitance.