The resonances of a resonant tunneling structure are probed by a magnetic field applied parallel to the interfaces, which enables us to investigate the local band structure in k space. By rotating the magnetic field in the plane of the interfaces, the energy surface at constant kw is investigated. Using this technique we have studied differently strained Si/Sii-.vGe.v quantum wells; we see a large anisotropy of the energy levels, with the symmetry axes of light holes and heavy holes being rotated 45° with respect to each other.
Resonant tunneling measurements are used to probe the inhomogeneous strain in individual SiGe quantum dots. Current–voltage characteristics of strained Si/SiGe resonant tunneling diodes of diameter D⩽0.25 μm exhibit additional fine quasi-periodic structure in the resonant peaks. The fine structure is consistent with lateral quantization in the SiGe quantum well due to in-plane confining potentials arising from inhomogeneous strain, which we calculate by finite element techniques for various D. Quenching of the fine structure by a magnetic field is consistent with the effective length scale of the strain-induced potential.
The effect of a parasitic parallel conducting layer on the measurement of longitudinal and transverse magnetoresistances of a high mobility two-dimensional (2D) electron gas in modulation-doped heterostructures is considered. A circuital analysis which takes into account the effect of circulating currents at the Hall contacts is presented, and previous descriptions of this situation are shown to be inapplicable. The resultant equations correctly predict the behavior of the longitudinal and transverse magnetoresistances at both high and low magnetic fields, and correlate well with the measured values. They also allow one to accurately determine the 2D mobility and density as well as the parallel layer resistivity.
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