Intrinsic bistability, self-consistency, and transport properties in novel resonant tunneling structures.

摘要

The interplay between charge confinement and intrinsic bistability is studied within the context of three distinct double-barrier resonant tunneling structures. Electrostatic feedback from electrons confined in the central quantum well of a conventional double-barrier diode modifies the potential drops across the two barriers, thus shifting the alignment between the emitter Fermi level and the quasibound state. Spacer layers positioned outside the double-barrier region which incorporate alternately light and heavy doping produce well-like features in the conduction-band profile which also give rise to multiple charge configurations. It is found that the number of solutions is limited by the requirement of self-consistency between the Schrodinger and Poisson equations. We then develop a phenomenological model which explains the bistability and hysteresis in operating current recently reported for a type-II resonant tunneling structure. This device is based on the double-barrier {dollar}InAs/Alsb{lcub}x{rcub}Gasb{lcub}1-x{rcub}Sb (0.4le xle0.6){dollar} materials system and can exhibit room-temperature current densities in excess of {dollar}rm2.5times10sp5 A/cmsp2.{dollar} The dual states correspond to two distinct amounts of charge residing in the electron and hole pockets created by the type-II band offsets. Our simulations indicate that tunneling between heavy- and light-hole levels plays a fundamental role in modifying the potential distribution across the structure via charge transfer between the two barriers. In addition, such transfer is found to be suppressed if the active layers of the device are made sufficiently thick, shallow, or asymmetric. We also explore the possibility of utilizing a double-barrier diode as the coupling mechanism between two classical superconductors to induce large gains in the critical supercurrent flowing through the structure. Resonance effects arising from an optimal alignment between the Fermi level and the subband eigenenergies in the well are shown to enhance the current by up to four orders of magnitude.