Since the initial proposal by Esaki and Tsu [1] and the advent of MBE, the interest in semiconductor superlattices (SLs) and quantum well (QW) structures has increased continuously over the years, driven by technological challenges, new physical concepts and phenomena as well as promising applications. A new class of materials and heterojunctions with unique electronic and optical properties has been developed. Here we focus on devices that involve infrared excitation of carriers in low dimensional solids (quantum wells, quantum dots, and superlattices). A distinguishing feature of these infrared detectors is that they can be implemented in chemically stable wide bandgap materials, as a result of the use of intraband processes. On account of this, it is possible to use such material systems as GaAs/AlxGa1-xAs (GaAs/AlGaAs), InxGa1-xAs/InxAl1-xAs (InGaAs/InAlAs), InSb/InAs1-xSbx (InSb/InAsSb), InAs/ Ga1-x InxSb (InAs/GaInSb), and Si1-xGex/Si (SiGe/Si), as well as other systems, although most of the experimental works have been carried out with AlGaAs. Some devices are sufciently advanced that there exists the possibility of their incorporating in high-performance integrated circuits. High uniformity of epitaxial growth over large areas shows promise for the production of large area two-dimensional arrays. In addition, exibility associated with control over composition during epitaxial growth can be used to tailor the response of quantum well infrared detectors to particular infrared bands or multiple bands.