Intersubband absorption in Si1−xGex/Si superlattices for long wavelength infrared detectors

We have calculated the absorption strengths for intersubband transitions in n-type Si1−xGex/Si superlattices. These transitions can be used for the detection of long-wavelength infrared radiation. A significant advantage in Si1−xGex/Si superlattice detectors is the ability to detect normally incident light; in Ga1−xAlxAs/GaAs superlattices intersubband absorption is possible only if the incident light contains a polarization component in the growth direction of the superlattice. We present detailed calculations of absorption coefficients, and peak absorption wavelengths for [100], [111], and [110] Si1−xGex/Si superlattices. Peak absorption strengths of about 2000–6000 cm−1 were obtained for typical sheet doping concentrations (≊1012 cm−2). Absorption comparable to that in Ga1−xAlxAs/GaAs superlattice detectors, compatibility with existing Si technology, and the ability to detect normally incident light make these devices promising for future applications.