ABSTRACT
The terms “intersubband” (ISB) or “intraband” refer to electronic transitions between confined states in either the conduction band or the valence band of semiconductor heterostructures. The first measurement of ISB absorption in GaAs quantum wells (QWs) was performed by West and Eglash, (West and Eglash 1985) and the results which led to the fabrication of the first QW infrared photodetector (QWIP) (Levine et al. 1987; Levine 1993). In 1994, Faist et al. (1994) presented a major breakthrough in the ISB technology: the quantum cascade laser (QCL). This was the beginning of the tremendous development of the ISB technology, which resulted in commercially available infrared (IR) optoelectronic devices. For an introduction to ISB physics, we refer the readers to Bastard (1988) or Liu and Capasso (2000).
