Quantum magnetotransport studies of semiconductor heterostructure devices
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. Resonant interband tunneling is perhaps the most generalized example of quantum transport in semiconductor heterosystems, and yet few studies of interband magnetotunneling have been...
| Summary: | NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.
Resonant interband tunneling is perhaps the most generalized example of quantum transport in semiconductor heterosystems, and yet few studies of interband magnetotunneling have been reported. This thesis presents the results of the first in-depth study of quantum magnetotransport through valence band-like well states in broken-gap semiconductor heterostructures. The transport characteristics of a series of InAs/AlSb/GaSb/AlSb/InAs resonant interband tunneling (RIT) diodes were investigated in magnetic fields as great as 8 tesla oriented both parallel and perpendicular to the tunnel current density. The resulting observations advance the understanding of interband transport and reveal interesting and complex phenomena previously unseen in magnetotunneling investigations.
In magnetic fields perpendicular to the tunnel current density, evidence of both low-mass, negative dispersion, and high-mass, positive dispersion states in the GaSb well is shown. The magnetic field in this geometry has no discernible effect on the RIT transport characteristics at low fields, however, and the transition between this low-field regime, and the expected response at higher field strengths is extremely abrupt. Associated with this marked change in behavior is an additional, narrow peak present in the negative differential resistance (NDR) region of the device at the threshold, or critical, magnetic field. This anomalous discontinuity in device transport violates semi-classical theory and is suggestive of a dramatic and fundamental change in resonant quantum transport.
With the field applied normal to the epitaxial layers, Landau levels form and resonant tunneling through them is observed indirectly via Shubnikov-de Haas-like oscillations of the tunneling conductance. The non-conservation of Landau level index in interband magnetotunneling is first proposed theoretically, and subsequently verified experimentally. Evidence for this effect is asserted from the discontinuous changes in the Shubnikov-de Haas oscillatory phase as a function of applied bias. These phase shifts result from bias-dependent changes in the resonant current path through well hole states of differing longitudinal angular momentum. The data are the first observation of Landau level mixing in interband tunnel devices, and only the second report for magnetotunneling in general. The lack of separate Shubnikov-de Haas oscillations for coupling to spin-up and spin-down states is interpreted to be evidence that the well masses are significantly less than the electrode mass, such that the reduced mass [...] of the two is approximately equal to the well mass, [...].
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