3 $mu$m intersubband quantum well photodetector (QWIP)

Abstract

In recent years photodetectors operating in the mid- to far infrared region of 3-15 $mu m$ have been designed based on electron and hole intersubband transitions in multiple quantum wells and superlattices. In general, QWIPs based on electron transitions show greater detectivity compared to the hole-based photodetectors. However, selection rules for electron intersubband transitions usually forbid the TE mode operation, associated with normal light incidence; Therefore, special coupling structures/geometries have been employed to couple light into the device. The spectral region 3-5 $mu m$ is of interest for a variety of applications such as environmental gas sensing, thermal imaging etc. and is not well covered by existing detectors. We have grown a QWIP operating at $sim 3mu m$ with a normal incidence component which incorporates an InGaAs/GaAs asymmetric quantum well from which photo-excited carriers undergo resonant tunnelling into the AlGaAs barriers. A study of temperature-dependent dark current of this device is presented with a view to obtaining enhanced detectivity at high temperatures.