Effects of high space-charge fields on the impulse response of the metal–semiconductor–metal photodiode

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 analyse their high-speed response and quantum efficiency at high energy levels of the optical illumination. Different collection rates of the carriers result in space-charge fields and partial screening of the dark internal electric field. This effect gives rise to impulse response distortion and degradation of the quantum efficiency. Several ways of improving the high-speed response of the MSM–PD are analysed. The conditions for neglecting space charge effects are formulated. Modelling data are compared with experimental results on GaAs-based MSM–PD.