GaAs MSM photodetectors with recessed anode and/or cathode

The GaAs metal-semiconductor-metal photodetectors (MSM-PD's) with recessed electrodes have been systematically characterized. The recessed cathode results in effective collection of the speed-limiting holes due to both a strengthened electric field and a shortened transit path around the absorption region while the recessed anode gives no significant change on the electric field distribution, as evidenced by the two-dimensional simulation. The experimental results show that the MSM-PD's having the recessed-cathode structure, compared with the conventional one, exhibit a substantial improvement on the speed, peak amplitude, and capacitance, especially at low-bias operation. The fall time of the temporal response approaches its saturation value of about 10 ps at a bias voltage as low as 3 V on the 50 μm × 50 μm detector with a finger width and spacing of 2 μm.