Dark current suppression in GaAs metal-semiconductor-metal photodetectors

We demonstrate a novel technique for decreasing the dark current in GaAs and AlGaAs-GaAs metal-semiconductor-metal (MSM) photodetectors without compromising the responsivity or the bandwidth. This technique involves the placement of the electrode tips and the contact pads on top of an insulating layer of silicon nitride to eliminate parasitic leakage paths and high electric field regions near the tips of the electrodes. For GaAs devices biased at 5 V with a 50×50-μm² active area and 3-μm electrode spacing and width, the dark current was reduced from 48.8 to 2.49 nA and the noise equivalent power was reduced from 119 to 26.9 nW. For similar AlGaAsGaAs devices, the dark current was reduced from 1.6 to 0.3 nA and the noise equivalent power was reduced from 19.2 to 8.12 nW.