Thermionic emission acrossAlxGa1−xAs single barriers under hydrostatic pressure

We have investigated thermally activated transport across GaAs-${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As-GaAs single-barrier heterostructures under hydrostatic pressures up to 6 kbar. The pressure dependence of the activation energy Φ is measured for different mole fractions x in the alloy barrier. For all samples with X≥0.50, Φ decreases with a pressure coefficient of 17±2 meV ${\mathrm{kbar}}^{\mathrm{-}1}$, indicating the importance of the X valleys in the activated current. However, for a barrier with x=0.38, Φ is only observed to decrease above a pressure threshold of 2 kbar, and no decrease is observed at all for a barrier with x=0.33. In addition to the pressure dependence of the activation energy, an influence of pressure on the prefactor of the activated current is observed. The results are interpreted in terms of a model that takes into account two different transport channels, one via the Γ point and the other via the X point in the ${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As barrier.