We describe a novel GaAs/AlGaAs double-quantum-well device for the infrared photon detection , called Charge-Sensitive Infrared Phototransistor ( CSIP ) .
The principle of CSIP detector is the photo-excitation of an intersubband transition in a QW as an charge integrating gate and the signal amplification by another QW as a channel with very high gain , which provides us with extremely high responsivity ( 10 ^ { 4 } – 10 ^ { 6 } A/W ) .
It has been demonstrated that the CSIP designed for the mid-infrared wavelength ( 14.7 \mu m ) has an excellent sensitivity ; the noise equivalent power ( NEP ) of 7 \times 10 ^ { -19 } W/ \sqrt { Hz } with the quantum efficiency of \sim 2 \% .
Advantages of the CSIP against the other highly sensitive detectors are , huge dynamic range of > 10 ^ { 6 } , low output impedance of 10 ^ { 3 } – 10 ^ { 4 } Ohms , and relatively high operation temperature ( > 2 K ) .
We discuss possible applications of the CSIP to FIR photon detection covering 35 – 60 \mu m waveband , which is a gap uncovered with presently available photoconductors .