Abstract
In this article we present a theoretical investigation of the tunnelling current in resonant tunnelling diodes based on a realistic tight-binding approach. The hydrostatic pressure dependence of the tunnelling current is calculated and compared with available experimental results. An important contribution from the X valley of the barrier region is demonstrated, which becomes especially significant at high pressures. The level crossing between X and Gamma localized states is shown to modify the peak value of the tunnelling current.