# CSIP - a Novel Photon-Counting Detector Applicable for the SPICA Far-Infrared Instrument

## TL;DR

The paper introduces a novel GaAs/AlGaAs quantum-well photon detector, CSIP, with high responsivity and sensitivity, suitable for far-infrared applications, filling a gap in current detector technology.

## Contribution

A new charge-sensitive infrared phototransistor (CSIP) device with high responsivity, low noise, and broad wavelength applicability for FIR photon detection is proposed and characterized.

## Key findings

- Achieved NEP of 7x10^-19 W/Hz with ~2% quantum efficiency.
- Demonstrated high dynamic range >10^6 and operation above 2K.
- Potential to detect 35-60 um FIR photons filling existing technological gaps.

## Abstract

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 um) has an excellent sensitivity; the noise equivalent power (NEP) of 7x10^-19 W/rHz with the quantum efficiency of ~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 (>2K). We discuss possible applications of the CSIP to FIR photon detection covering 35 -- 60 um waveband, which is a gap uncovered with presently available photoconductors.