Advantages of an indirect semiconductor quantum well system for infrared detection

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Abstract
We have analyzed the infrared intersubband absorption process in quantum well systems with anisotropic bulk effective masses, which usually occurs in indirect semiconductors. We find that the anisotropic effective mass can be utilized to provide allowed intersubband transitions at normal incidence to the quantum well growth direction. This transition is known to be forbidden for cases of isotropic effective mass. This property can be exploited for infrared sensor application of quantum well structures by allowing direct illumination of large surface areas without using special waveguide structures. We have calculated the 10-μm intersubband absorption in quantum wells made of the silicon-based system Si/Si1−xGex. We find that it is readily possible to achieve an absorption constant of the order of 104 cm−1 in these Si quantum wells with current doping technology.