High-responsivity InGaAs MSM photodetectors with semi-transparent Schottky contacts

High-performance metal-semiconductor-metal photodetectors (MSM-PD´s) with interdigitated semi-transparent Au Schottky contacts have been fabricated on pseudomorphic In/sub 0.9/Ga/sub 0.1/P-InP-InGaAs heterostructure. The responsivity measured at 1.55-μm wavelength is greatly enhanced from 0.4 A/W to 0.7 A/W as the thickness of the Au electrodes is decreased to 10 nm. This corresponds to a 75% improvement over the conventional MSM-PD´s with opaque metal electrodes. With a pseudomorphic InGaP barrier-enhancement layer, these devices exhibit a dark current density as low as 1.6 pA/μm². Extremely linear photoresponse without any internal gain is also observed for these detectors. The full-width at half maximum of the temporal response for the devices with semi-transparent electrodes is about 85 ps compared to 80 ps for the conventional ones.