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

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.