High-Frequency Response of Metal-Semiconductor-Metal Photodetectors Limited by Dynamic and Recombination Effects

A simplified quasi-two-dimensional analytical model of planar interdigitated metal-semiconductor-metal (MSM) photodetectors is presented. The model takes into account the transit-time and velocity overshoot effects of photogenerated electrons and holes and their recombination. The response is derived as a function of the signal frequency and the device structural parameters. It is shown that MSM photodetectors with relatively large contact spacing can exhibit rather high-frequency response in the terahertz range due to electron velocity overshoot. The obtained MSM photodetector response is in good agreement with the results of a Monte Carlo simulation. The response-frequency product reveals a high maximum corresponding to a frequency of about a few terahertz. The MSM photodetectors exploiting the velocity overshoot effect can be advantageous in comparison to the MSM photodetectors with ultrashort lifetime of the photogenerated electrons and holes.