A differential photoconductive AND gate with Be-doped low-temperature-grown InGaAs-InAlAs MQW MSM-PD's

A novel photoconductive AND gate that overcomes the problems of: 1) the long tail of photoconductive switches and 2) signal leakage via switch capacitance (signal feedthrough) is proposed. We use Be-doped low-temperature (LT)-grown InGaAs-InAlAs MQW metal-semiconductor-metal photodetectors (MSM-PD's) to get a shorter turn-off time and propose a differential AND gate to cancel the signal feedthrough. A comparison between LT-grown MSM-PD's and those fabricated by ion implantation shows that the LT-grown ones are ultrafast with a full width at half maximum of 5.3 ps and are suitable for low-bias operation. It is experimentally confirmed that the differential AND gate completely cancels the signal feedthrough in the picosecond region. The differential AND gate: with the LT MSM-PD's achieves return-to-zero (RZ) 20 Gb/s AND operation.