Vertical transport in a GaInAsSb∕p-InAs broken-gap type II heterojunction

The formation of self-consistent quantum wells for electrons and holes in a P(N)-GaInAsSb∕p-InAs broken-gap type II heterojunction with an abrupt planar interface (a transition layer of the order of 1.2nm thick) upon variation of the type and level of doping of the semiconductors in contact is controlled by the overlap of the energy bands at the heterointerface. In a study of the vertical magnetotransport through a GaInAsSb∕p-InAs broken-gap type II heterointerface it is shown that the increase of the localization of the two-dimensional electrons in the electron channel at the interface leads to the formation of a “soft” Coulomb gap in the tunneling density of states. In magnetic fields below 15T at helium temperature a transition from the state with a “soft” Coulomb gap to an insulator state (a hard energy gap at a conductance value of σtun∼10−8Ω−1) is observed under the condition that the Fermi level for the two-dimensional electrons lies in the interval between the lowest Landau levels for the ν=2 plateau on the ρxy curve. As the external bias across the heterojunction is increased, the threshold offset from the insulator state is due to one-electron tunneling between individual closed regions of extended electronic states of the Landau level closest to the Fermi level.