Properties of InAs/InAlAs heterostructures

InAs is the only binary III-V compound semiconductor that exhibits a natura l surface accumulation due to the high density of donor surface states. The Fermi level is pinned at any surface of an InAs wafer, regardless of orien tation. It is therefore very likely that an accumulation layer is present a t both the top and bottom surface or interface of a thin InAs epilayer with an intermediate bulk-like region between them. Epitaxial layers of InAs sa ndwiched between two 30 nm thick layers of In0.8Al0.2As or In0.52Al0.48As w ere grown on InP substrates by solid-source molecular beam epitaxy. Their s tatic and dynamic properties were determined by means of gated Hall, resist ivity and C-V measurements using a three-layer model to account for interfa ce accumulation as well as the residual bulk-like intermediate region. The InAs/In0.8Al0.2As heterojunction interface has a significantly lower densit y of interface states than that of the In0.52Al0.48As/InAs interface. It is possible to drive such a structure from accumulation through flat band int o depletion by means of moderate negative gate voltages. Using similar meas urements, the effect of the thickness of the InAs layer as well as the pres ence or absence of a step-graded buffer on the density of surface states wa s determined.