ALL-GAAS ALGAAS READOUT CIRCUIT FOR QUANTUM-WELL INFRARED DETECTOR FOCAL-PLANE ARRAY/

We report the fabrication and testing of all-GaAs/AlGaAs hybrid readou t circuit operating at 77 K designated for use with an GaAs/AlGaAs bac kground-limited quantum-well infrared photodetector focal plane array (QWIP FPA). The circuit is based on a direct injection scheme, using s pecially designed cryogenic GaAs/AlGaAs MODFET's and a novel n(+)-GaAs /AlGaAs/n(+)-GaAs semiconductor capacitor, which is able to store more than 15 000 electrons/mu m(2) in a voltage range of +/-0.7 V. The sem iconductor capacitor shows little voltage dependence, small frequency dispersion, and no hysteresis. We have eliminated the problem of low-t emperature degradation of the MODFET I-V characteristics and achieved very low gate leakage current of about 100 fA in the subthreshold regi me. The MODFET electrical properties including input-referred noise vo ltage and subthreshold transconductance were thoroughly tested. Input- referred noise voltage as low as 0.5 mu V/root Hz at 10 Hz was measure d for a 2 x 30 mu m(2) gate MODFET. We discuss further possibilities f or monolithic integration of the developed devices.