Abstract

MSM photodetectors are attractive for integration with receiver circuits since they have lower capacitance than p-i-n detectors with the same surface area. Low external quantum efficiency (20% to 40%), however, is a disadvantage of MSMs, which is primarily due to finger electrode shadowing. Several research teams had investigated novel ways to enhance the quantum efficiency such as transparent indium tin oxide electrodes (ITO-MSM) [1], and a Bragg mirror on the bottom to define a Fabry-Perot cavity [2]. The ITO MSMs demonstrated much higher quantum efficiency, but speed degradation was also noted due to the high resistivity ITO contacts. The Bragg mirror design produced only a moderate increase in efficiency. In this paper, inverted MSMs (I-MSMs), with metallized fingers on the bottom of the MSMs, are reported at 850 nm in GaAs/AIGaAs, with record external quantum efficiency for normal incidence MSMs at this speed.

© 1996 IEEE