InAsSb/InAs: A type-I or a type-II band alignment

Using first-principles band-structure calculations we have studied the valence-band alignment of InAs/InSb, deducing also the offset at the ${\mathrm{InAs}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Sb}}_{\mathit{x}}$/${\mathrm{InAs}}_{1\mathrm{-}\mathit{y}}$${\mathrm{Sb}}_{\mathit{y}}$ heterostructure. We find the following: (i) Pure InAs/InSb has a ‘‘type-II broken gap’’ alignment both with and without strain. (ii) For Sb-rich ${\mathrm{InAs}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Sb}}_{\mathit{x}}$/InSb heterostructures, the unstrained band alignment is type II; both epitaxial strain and CuPt ordering enhance the type-II character in this Sb-rich limit. (iii) For As-rich InAs/${\mathrm{InAs}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Sb}}_{\mathit{x}}$ heterostructures the top of the valence band is always on the alloy layer while the conduction-band minimum can be localized either on the alloy layer (type-I) or on the InAs layer (type-II), depending on the balance between concentration, strain, and degree of ordering/phase separation. In this case, epitaxial strain enhances the type-II character, while ordering enhances the type-I character. Our results are compared with recent experimental observations. We find that the type-I behavior noted for some As-rich InAs/${\mathrm{InAs}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Sb}}_{\mathit{x}}$ interfaces and the type-II behavior noted in other such samples could be explained in terms of the dominance of ordering and strain effects, respectively.