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

We report the fabrication and testing of an 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/sup +/-GaAs/AlGaAs/n/sup +/-GaAs semiconductor capacitor, which is able to store more than 15 000 electrons//spl mu/m/sup 2/ in a voltage range of /spl plusmn/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 /spl mu/V//spl radic/Hz at 10 Hz was measured for a 2/spl times/30 /spl mu/m/sup 2/ gate MODFET. We discuss further possibilities for monolithic integration of the developed devices.