A simple high-speed Si Schottky photodiode

Design, fabrication, and UV-heterodyne characterization of Ni-Si-Ni metal-semiconductor-metal (MSM) Schottky barrier photodetectors is reported. Planar detectors were fabricated, with a simple 3-level lithography process on bulk Si, in both simple-gap and interdigitated geometries with gap dimensions from 1 to 5 mu m. Frequency response of these devices was characterized using a CW-laser heterodyne system at 334.5 nm. For a 4.5- mu m interdigitated device, a 3-dB response of 16 GHz is measured, giving 22 GHz when deconvolved from the package/connector. A detailed theoretical model of the photodiode response incorporating effects of carrier transport and device geometry is in excellent agreement with the measurement. This model predicts a 86-GHz 3-dB response for the 1- mu m gap geometry devices.>