Transit-time considerations in metal–semiconductor–metal photodiode under high illumination conditions

Abstract

A two-dimensional self-consistent time-dependent simulation technique has been used to investigate electron–hole transport processes in the active region of metal–semiconductor–metal photodiode structures (MSM-PD) and to analyze their high-speed response at different energy levels of the optical illumination. Charge accumulation and screening of the dark electric field at high optical excitation levels greatly modify the drift conditions of the photogenerated electrons and holes in the active region of the MSM-PD. This effect gives rise to impulse response distortion and reduced bandwidth and efficiency. Some ways of improving the high-speed response of the MSM-PD are analyzed and discussed. The conditions under which screening of the internal field has no effect on the MSM-PD response are formulated. It is shown that large active area MSM-PDs have considerable advantages over smaller area devices in their ability to detect high energy levels of optical radiation without saturation and distortions.