Enhanced long wavelength response in a GaAs photodetector

A metal-semiconductor-metal photodetector (MSM-PD) fabricated on a semi-insulating GaAs has a long wavelength response beyond the energy gap. It is enhanced by applying a second bias voltage to the bottom electrode. When the bias is 100 V, the responsivity exceeds the unit quantum efficiency, which indicates that a photoconductive amplification function exists. Since the dark current is as small as 0.2 nano-amperes, it may be more suitable than an InGaAs or a Ge photodiode for long wavelength detection.