Abstract

Recently we have demonstrated¹ that the intrinsic speed of defect-free interdigitated metal-semiconductor-metal (MSM) photodetectors with a thin light-absorbing InP cap layer on top of a reservoir GaInAs layer is comparable to defect-rich low-temperature-grown MSM diodes,² Here, we report on the physical mechanism responsible for this ultrafast response. Through a combination of electro-optic sampling and luminescence up-conversion measurements, we identify ultrafast charge transfer from the InP layer to the GaInAs layer underneath³ as the relevant mechanism. This transfer enhances the bandwidth of the diode through an ultrafast current cutoff. The carriers trapped in the GaInAs layer recombine on a time scale much longer than the transfer time. Thus, they do not contribute significantly to the photocurrent if the electrical bias is set to a moderate level at which the carriers remain confined.

© 1993 Optical Society of America