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The charge distribution at a semiconductor-insulator interface has been calculated, both for holes and electrons, by solving Schrödinger’s and Poisson’s equations self-consistently for particles obeying Fermi–Dirac statistics. The results have been applied to carriers in the channel of a crystalline MOSFET (metal-oxide-semiconductor field-effect transistor) with the (100) axis perpendicular to the gate oxide. For weak inversion, the self-consistent results do not deviate significantly from those obtained assuming a triangular potential well, but for strong inversion the carriers tend to move closer to the oxide. The energy and occupation levels of the subbands are only affected by a few percent on passing from weak to strong inversion, keeping the transversal interface electric field fixed. Finally the gate capacitance has been calculated and found to agree with the experimental data published elsewhere.

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We present a comprehensive theoretical and experimental analysis of the current response of GaAs metal-semiconductor-metal Schottky photodiodes exposed to 70 fs optical pulses. Theoretical simulations of the carrier transport in these structures by a self-consistent two-dimensional Monte Carlo calculation reveal the strong influence of the distance between the finger electrodes, the external voltage, the GaAs layer thickness and the excitation intensity on the response time and the corresponding frequency bandwidth of these photodetectors. For many experimental conditions, the model demonstrates a clear temporal separation of the electron and hole contributions to the output current due to the different mobilities of the two carrier types. For a diode with an electrode separation of 0.5 μm, an electric-field strength above 10 kV/cm and low intensity of the incident light the theory predicts a pulse rise time below 2 ps, an initial rapid decay as short as 5 ps associated with the electron sweep out and a subsequent slower tail attributed to the hole current. For weaker electric fields and/or higher light intensities a significant slowing down of the detector speed is predicted because of effective screening of the electric field by the photoexcited carriers. Heterostructure layer-based devices are shown to provide superior performance compared to diodes manufactured on bulk substrates. Experimental data obtained by photoconductive or electro-optic sampling on diodes with electrode separation between 0.5 and 1.2 μm agree fairly well with the theoretical predictions.