Low-frequency gain in MSM photodiodes due to charge accumulation and image force lowering

To understand the nature of low-frequency gain in MSM photodiodes, Schottky barrier height was measured for an MSM photodiode fabricated on GaAs-based layers. The Schottky barrier height showed a dependence on the light irradiation and bias. This can be explained by a lowering of the Schottky barrier due to charge accumulation at surface states and image-force lowering at the edges of metal electrodes where electric field is extremely high. Thermionic hole emission is proposed as a source of low-frequency gain of MSM photodiodes.