ABSTRACT
Since the initial observation of strong intersubband absorption and sensitive direct detection in GaAs multiple quantum well (MQW), detectors made from these structures have been the prototype for a new class of infrared (IR) detectors. The disadvantages of the GaAs MQW direct detector are also well known because they have been a major impediment to the implementation of these devices in IR staring arrays. The most successful quantum-well detectors studied to date have been based on the bound-to-extended-state mode. In this mode an incoming photon polarized perpendicular to the plane of the quantum well excites an electron from the ground state directly to the first extended state above the barriers. The polarization rules associated with intersubband absorption in ellipsoidal-valley and spherical-valley quantum wells can be understood from the following classical argument. In addition to providing a more convenient absorption than GaAs quantum wells, ellipsoidal-valley quantum wells can, in principle, exhibit much less dark current.
