Intrinsic and extrinsic response of GaAs metal-semiconductor-metal photodetectors

Simulation of GaAs metal-semiconductor-metal (MSM) photodetectors using a self-consistent Monte Carlo (MC) method is discussed. Intrinsic device properties are discussed in terms of MC electron and hole transport under low illumination intensity. Parasitic circuit elements are then introduced to more closely model realistic devices using the MC results in a circuit simulator. Intrinsic devices with 0.5- and 1.0- mu m spacing between fingers are dominated by stationary high-field transport. Surprisingly, full-width-half-maximum (FWHM) of 0.5- and 1.0- mu m detectors with parasitics is 4.3 and 3.8 ps, respectively. However, the 1- mu m detector exhibits a long hole tail and transient oscillations. Thus, FWHM results (and intrinsic device response) can be inadequate predictors of ultimate frequency response and scaling behavior. However, an estimate of maximum repetition frequency gives f/sub max/=92 GHz for the 0.5 mu m device, consistent with experimental data.<>