High pressure studies of negative differential resistance in InAs/GaSb resonant conduction heterostructures

A single heterojunction of n-InAs/p-GaSb behaves as a two dimensional electron gas (2DEG) back to back with a two dimensional hole gas (2DHG), due to overlap between the GaSb valence band and the InAs conduction band. An unusual feature is the possibility of growing a 'light' GaAs or a 'heavy' InSb interface. The two interface types are predicted to give rise to different electronic and vibrational properties, while the existence of monolayer steps or interdiffusion could give rise to a mixed interface character. In this paper we demonstrate that vertical transport measurements as a function of pressure are a sensitive way of probing the electronic structure of the interface. On biasing InAs negative with respect to GaSb, electron transfer takes place from the 2DEG to the 2DHG, and the current initially increases with bias. At a critical bias, quantum confinement raises the energy of the 2DEG above that of the 2DHG and a region of Negative Differential Resistance (NDR) then occurs. The size of the NDR feature and the critical bias are both reduced by hydrostatic pressure, showing that the band overlap decreases. For a number of samples grown with a heavy interface by atmospheric pressure metalorganic vapour phase epitaxy the NDR vanishes at a threshold, P_c ~ 12 ± 2 kbar. This threshold is consistent with a band overlap of 120 ± 20 meV and a shift of -10 meV/kbar. The NDR properties are found to be very sensitive to the detailed sequence of switching of the precursors during interface growth, as well as to the interface type.