Tunneling resonances at high pressure in double-barrier structures with AlAs barriers thicker than 50 Å

For pressures above those required to induce the type-I-to-type-II transition, we examine the low bias electronic properties of three AlAs/GaAs double-barrier structures in which the width of at least one of the AlAs layers is 50 {} or more. We observe that the previously reported suppression at low temperature of the low bias X-related resonances is removed when the emitter state lies in a thick barrier, and this is explained by a reversal in the ordering of Xₜ(1) and Xₗ(1), where Xₜ(n) and Xₗ(n), respectively, are the nth confined subband associated with the four transverse and the two longitudinal X minima. We demonstrate for the asymmetric structures that the clearest resonances at high pressure occur in the opposite bias direction to that which gives the strongest resonances at ambient pressure.