Quantification of atomic intermixing in short-period InAs/GaSb superlattices for infrared photodetectors

Abstract

Cross-sectional scanning tunneling microscopy (XSTM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) are applied for characterizing the MBE-grown short-period InAs/GaSb superlattices for mid- and long-wavelength infrared detection. The focus of this study is on atomic intermixing in close proximity to the interfaces, which is a key issue for device performance. HAADF-STEM permits visualization of the anion-cation dumbbells in individual sub-layers and is even capable to resolve anions and cations separated by 0.15 nm within a dumbbell. On this basis, the interfacial width is extracted with high accuracy. XSTM technique allows us direct counting of certain kinds of atoms within atomic rows, which sheds light on compositional fluctuations and isovalent atomic intermixing. Both methods reveal rather abrupt interfaces with InAs-on-GaSb interfaces being slightly wider than GaSb-on-InAs interfaces. According to HAADF-STEM, in the set of investigated samples, the 90%-to-10% interface width is confined within 2.6–4.4 monolayers (0.8–1.3 nm). In all the samples studied, XSTM analysis showed some residual concentration (on the level of a few atomic percent) of Sb atoms in the middle of the InAs sub-layers, as a result of As/Sb substitutions during growth. The level of intermixing is diminishing with increasing the thickness of individual InAs layers.