Impulse responses of submicron GaAs photodetectors

Metal–semiconductor–metal photodetectors with different submicron spacings (d = 100, 300, 500, 700 and 900 nm) were fabricated on GaAs with a carrier recombination time of 100 ps by electron beam lithography. Temporal responses of the detectors were measured by photoconductive sampling in order to identify factors which limits the response speeds. At a low excitation of <100 μW, the response speeds of 100, 300 and 500 nm spacing detectors are limited by parasitic capacitances of the submicron structures. The speeds of 700 and 900 nm spacing detectors are limited by an electron/hole transport in the semiconductor. At a high excitation of >100 μW, the response speeds of the all spacing detectors are limited by field screening caused by electron–hole plasma.