Magnetotransport probing of the quality of the heterointerfaces and degree of symmetry of the potential profile of quantum wells in the valence band of the Ge1−xSix/Ge/Ge1−xSix heterosystem

Abstract

It is shown that in a periodic system of p-type Ge1−xSix/Ge/Ge1−xSix quantum wells having a Ge layer more than ∼30 nm wide, the hole gas in each Ge layer is separated into two two-dimensional sublayers concentrated near opposite boundaries of the layer. This follows from the vanishing of the quantum Hall effect plateau and of the corresponding minimum of the longitudinal magnetoresistance for a filling factor ν=1. Here positive magnetoresistance is observed, which is attributed to the presence of two types of holes with different mobilities. A quantitative analysis shows that these are mainly heavy holes having different mobilities in the sublayers that form. The difference of the mobilities indicates that the opposite heterointerfaces of the Ge layers are of different quality. It follows from an analysis of the shape of the quantum Hall effect plateau for ν=2 that the densities of holes in the sublayers formed are close and, consequently, that the profile of the potential wells is close to symmetric.