Type-II InAs/GaInSb superlattices for terahertz range photodetectors

Abstract

We designed InAs/Ga_0.6In_0.4Sb superlattice (SL) material for terahertz-range photodetectors. Depending on the thicknesses of the InAs and Ga_0.6In_0.4Sb layers, the SL energy gap Eg can be adjusted to be between 8-25 meV, which corresponds to a cut-off frequency from 2 to 6 THz. Different designs were numerically evaluated by using the eightband k•p model. The calculations show that the SL energy gap is sensitive to monolayer (ML) scale variations in layer thickness, and that realization of the design parameters requires better than 1ML accuracy of epitaxial growth. A 40-period strained Ga_0.6In_0.4Sb SL with alternating InSb (1ML) and GaAs (1ML) interfaces was grown by a molecular beam epitaxy on a GaSb substrate; the target energy gap Eg was 9 meV. The SL samples were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), photoluminescence and absorption spectroscopy measurements. Despite the large lattice mismatch between InAs and Ga_0.6In_0.4Sb, the XRD and AFM measurements showed that the SL had good structural and surface quality and an accurate layer structure. The surface roughness was 0.22 nm.