Characteristics of QWIPs at low background

Quantum well infrared photodetectors (QWIPs) rapidly become mature in high background applications. On the other hand, the detector properties at low temperature and low background conditions are less well characterized. We h ave studied the current-voltage characteristics of QWIPs under this regime. We found that the current level in a fixed experimental condition can chan ge slowly and substantially with time. The slow time dependence leads to la rge current hysteresis upon thermal cycling at a finite cycling rate. Under certain conditions, this time constant can be exceeding long, which leads to different metastable current states, depending on the experimental histo ry, We also observed that in a long time scale, the de current level of a d etector need not be directly proportional to the background radiation. Spec ifically, we observed that the de current level of some detectors under F/1 6 can be larger than that under F/2 at 10 K and with 290 K background. We a ttribute these phenomena to the effects of unintentional dopants in the QWI P barriers. In addition, we found that the dominant noise in this regime is the 1/f noise caused by the DX centers in the barriers. (C) 2001 Elsevier Science B.V. All rights reserved.