DOUBLE-PEAKED DECAY OF TRANSIENT PHOTOCURRENTS IN GAAS METAL-SEMICONDUCTOR-METAL PHOTODETECTORS

A double peak is sometimes seen on a picosecond time scale in the deca y of the transient photoconduction of GaAs metal-semiconductor-metal s tructures. This is known from experiments on micron-scale structures o f both conventional and backgated design. A previous numerical simulat ion, using a drift-diffusion calculation and an idealized one-dimensio nal model of the conventional structure, shows that the double-peaked behavior can arise from the effect of the photogenerated carriers on t he internal fields. Here we extend this to a two-dimensional calculati on to investigate the photoconduction decay in both the conventional a nd backgated designs. We calculate the instantaneous distribution of c harge and field in the structures during and after a pulse of illumina tion, and we show for each design how the interplay of carrier and dis placement currents can produce intrinsically a nonmonotonic decay with features qualitatively like those seen experimentally. (C) 1997 Ameri can Institute of Physics.