Impulse response of a heterojunction MSM photodiode

A two-dimensional model is used to simulate drift of photogenerated carriers in the active region of high-speed photodiodes (metal-semiconductor-metal (MSM) rectifying contacts) that are made as a conventional planar structure and a structure with a heterojunction. These two types of photodiode structures are compared in terms of the impulse response and quantum efficiency. Variation of the planar MSM diode response with decreasing size of the interdigitated contact system is analyzed. The possibility of improving the speed of response of the MSM diode is discussed. It is shown that the structure with an InP/GaInAs heterojunction considerably modifies the transport of photogenerated carriers and remarkably improves the response speed.