New long-wavelength photodetector based on reverse-biased doping superlattices

Abstract

A new GaAs photodetector of low capacitance and with high sensitivity in the whole 0.8–1.4-μm wavelength range has been fabricated from GaAs doping superlattices grown by molecular beam epitaxy. The highly doped yet semi-insulating superlattice allows application of high reverse bias via selective n+ and p+ electrodes also at room temperature. The excellent photoresponse of the totally depleted device at energies far below the GaAs energy gap arises from the existence of pronounced tail states in the forbidden gap region of the superlattice. Under operating conditions the capacitance of the detector depends only on the electrode geometry and can thus be kept extremely low. This implies high-speed response of the device.