ELIMINATION OF LOW-FREQUENCY GAIN IN INALAS INGAAS METAL-SEMICONDUCTOR-METAL PHOTODETECTORS BY SILICON NITRIDE-PASSIVATION/

We report the reduction of low frequency gain and surface recombinatio n in InAlAs/InGaAs metal-semiconductor-metal (MSM) photodetectors, by surface passivation with plasma-enhanced chemical vapor deposition (PE CVD) of silicon nitride. A corresponding improvement in device speed, measured in the frequency-domain, is demonstrated. Large (100 mu m)(2) devices exhibit near-transit-time-limited bandwidth (>10 GHz) followi ng passivation, and device characteristics have been stable over a per iod of several months. We propose a physical model for electron trappi ng at the free surface, to explain the low frequency gain in nonpassiv ated devices and its subsequent elimination.