GaAs MSM photodetectors with recessed anode and/or cathode

The GaAs metal-semiconductor-metal photodetectors (MSM-PDs) 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-PDs 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 /spl mu/m/spl times/50 /spl mu/m detector with a finger width and spacing of 2 /spl mu/m.