A sensitive double quantum well infrared phototransistor

Abstract

An infrared phototransistor $(\sim 14.5\mu \mathrm{m})$ on a $\mathrm{Ga}\mathrm{As}∕\mathrm{Al}\mathrm{Ga}\mathrm{As}$ double quantum well (QW) heterostructure is studied. A confined upper QW behaves as a photoactive gate to a conducting channel formed by the lower QW. By properly biasing the narrow gates for isolating the upper QW island, the lateral tunneling rate of cold electrons on upper QW can be tuned and hence the lifetime of photocarriers on the QW island can be controlled. Associated with this controllable lifetime, photoresponse takes a sharp maximum, which reaches as high as $\sim {10}^3\mathrm{A}∕\mathrm{W}$ . Analysis in terms of a simple model suggests that the peak response originates from the interplay∕trade-off between the lifetime of photocarriers and the efficiency of photodetection process. The photodetection efficiency substantially varies as a consequence of large band bending induced by the $300\mathrm{K}$ thermal background radiation. The long (approximately millisecond order) and controllable lifetime in our device paves the way for future development of photon counters in the long wavelength range. In addition, our device has a good compatibility with standard GaAs integrated circuit technology.