All-GaAs/AlGaAs readout circuit for quantum-well infrared detector focal plane array

We report the fabrication and testing of all-GaAs/AlGaAs hybrid readout circuit operating at 77 K designated for use with an GaAs/AlGaAs background-limited quantum-well infrared photodetector focal plane array (QWIP FPA). The circuit is based on a direct injection scheme, using specially 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 semiconductor capacitor shows little voltage dependence, small frequency dispersion, and no hysteresis. We have eliminated the problem of low-temperature degradation of the MODFET I-V characteristics and achieved very low gate leakage current of about 100 fA in the subthreshold regime. The MODFET electrical properties including input-referred noise voltage and subthreshold transconductance were thoroughly tested. Input-referred noise voltage as low as 0.5 mu V/root Hz at 10 Hz was measured for a 2 x 30 mu m(2) gate MODFET. We discuss further possibilities for monolithic integration of the developed devices.