Long‐wavelength infrared detectors based on strained InAs–Ga1−xInxSb type‐II superlattices

We demonstrate that infrared detectors made from strained type‐II superlattices consisting of III–V semiconductors can have favorable properties for long‐wavelength (λc >10 μm) detection applications. We specifically consider InAs–Ga1−x Inx Sb strained‐layer superlattices with x≊0.4 . This is a type‐II superlattice where the conduction‐band minimum of InAs is lower in energy than the valence‐band maximum of Ga1−x Inx Sb. Electrons are localized in the InAs layers while holes are localized in the Ga1−x Inx Sb layers. Generally, in a type‐II superlattice such as InAs–GaSb, large absorption coefficients cannot be achieved at the small values of band gap necessary for long‐wavelength detection because the localization of electrons and holes in adjacent layers leads to small optical matrix elements. Therefore, small band gaps and large optical matrix elements appear to be two mutually exclusive requirements in the InAs–GaSb superlattice. Here, we show that it is possible to obtain large optical absorption coef...