Type-II InAs/GaSb superlattices for very long wavelength infrared detectors

Type-II superlattices (SLs) can be designed for semiconductor band gaps as large as View the MathML source down to semimetallic. This flexibility in design makes them an excellent candidate for infrared photodiodes with cut-off wavelengths beyond View the MathML source. There are relatively few options for high-performance infrared detectors to cover wavelengths longer than View the MathML source, especially for operating temperatures above View the MathML source. In the past few years, excellent results have been obtained on photoconductive and photodiode samples designed for infrared detection in the very long wavelength infrared (VLWIR) range View the MathML source. There is a variety of possible designs for these SLs which will produce the same narrow band gap by adjusting individual layer thicknesses, or indium content, in the InGaSb layer. Several of these different design options have been grown and characterized. These designs often require monolayer control per layer over hundreds of repeats in the SL. Photoresponse spectra for type-II SLs are compared to show how the design choices not only change the band gap but also the band structure, as reflected in features observed in the spectra. Theoretical modeling results are used to interpret the photoresponse spectra. SLs with cut-off wavelengths ranging from 15 to View the MathML source are covered.