Quantum dots-in-a-well infrared photodetectors

Novel InAs/InGaAs quantum dots-in-a-well (DWELL) infrared photodetectors are reported. These detectors, in which the active region consists of InAs quantum dots embedded in an InGaAs well quantum well, represent a hybrid between a conventional quantum well infrared photodetector (QWIP) and a quantum dot infrared photodetector (QDIP). Like QDIPs, the DWELL detectors display normal incidence operation without gratings or optocouplers while demonstrating reproducible “dial-in recipes” for control over the operating wavelength, like QWIPs. Using femtosecond spectroscopy, long carrier lifetimes have been observed in DWELL heterostructures suggesting their potential for high temperature operation. Moreover, the DWELL detectors also have demonstrated bias-tunability and multi-color operation in the mid wave infrared (MWIR, 3-5 μm), long wave infrared (LWIR, 8-12 μm) and very long wave infrared (VLWIR, >14 μm) regimes. We have recently realized LWIR 320 × 256 focal plane arrays (FPAs) operating at liquid nitrogen temperatures. One of the potential problems with these detectors is the low quantum efficiency, which translates into low responsivity and detectivity. Some solutions to mitigate these problems are suggested at the end of the paper.