Tunneling-current measurements in ${\mathrm{Ga}}_{1-x}{\mathrm{Al}}_x\mathrm{As}-\mathrm{GaAs}-{\mathrm{Ga}}_{1-x}{\mathrm{Al}}_x\mathrm{As}$ heterostructures under hydrostatic pressure show that nonresonant tunneling occurs preferentially through the lowest potential barrier, while resonant tunneling is determined solely by a $\Gamma$-point profile. For fixed voltages, the low-temperature current through a 100 Å-40 Å-100 Å structure with ${\mathrm{Ga}}_{0.60}$${\mathrm{Al}}_{0.40}$As barriers increased with pressure, up to 11 kbar. The rate of increase showed an abrupt rise at ∼4 kbar, which is attributed to tunneling through a $\Gamma -X$ barrier. This interpretation is consistent with a rapid increase of the tunneling current in AlAs-GaAs-AlAs, even at low pressures. On the other hand, a negative-resistance feature associated with resonant tunneling via quantum-well states, shifted smoothly to lower voltages with pressure, indicating that the energy of the confined states is established by a pressure-dependent $\Gamma$-point profile.

• Received 3 July 1986

DOI:https://doi.org/10.1103/PhysRevB.34.6026