Physics of Single Quantum Well Infrared Photodetectors

Although there has been extensive research1–8 on multi-quantum well infrared photodetectors (QWIPs), which typically contain many (~50) periods, there has been relatively limited experimental work9–11 (using a fixed frequency CO2 laser) done on QWIPs containing only a single quantum well. Recently, we have performed a complete series of experiments12–14 on single quantum well structures with n-type doped well, p-type doped well and un-doped well. These doped-single well detectors are, in fact, particularly interesting since they have exceptionally high optical gain compared to multi well detectors. The optical response of the undoped single quantum well detector is strongly dependent on the bias voltage because the well is filled by tunneling through a thin emitter barrier. In addition, their simple band structures allow accurate calculations of the bias voltage dependence of the potential profiles of each of the two barriers, band bending effects in the contacts, as well as charge accumulation (or depletion) in the quantum well. Therefore by comparing theory with experiment, one can achieve a better overall understanding of the optical and transport physics in these quantum well infrared photodetectors.