We present results of the fabrication and investigation of totally spatially localized crystalline structures. Low temperature photoluminescence exhibits structure that is best explained by a bottleneck for hole energy loss. This bottleneck is believed to be a direct consequence of the modification of the band structure by the fabrication-imposed potential and is believed to be the first evidence for total spatial quantization in a fabricated heterojunction system.
The Hall mobility of holes in silicon p-type inversion layers has been measured as a function of gate voltage (perpendicular electric field), inversion layer orientation [(100), (110), and (111) surfaces], direction of current flow within an inversion layer, and temperature. It has been shown that hole mobility in silicon inversion layers depends not only on the crystalline orientation of the inverted surface, but also on the azimuthal direction of current flow within the inversion layer. Thus, on the (110) silicon surface at room temperature, the inversion-layer hole mobility is 40% higher in the[l̄10] direction than in the [001] direction. Room-temperature piezoresistance tensors have been experimentally determined for inversion layers on the (100), (110), and (111) surfaces of silicon. It is found that, in general, the piezoresistance coefficients are not the same as those for the same directions in bulk silicon and that they depend on the orientation of the surface. The existence of these anomalous effects can be understood in terms of quantization of the carrier wavefunction in the surface channel, which is narrow compared with the carrier wavelength in bulk silicon. This quantization tends to depopulate that part of the Brillouin zone within which k⊥, the component of wavevector perpendicular to the surface, is small. If the dependence of energy on k is not quadratic, as is true for the valence band of silicon, the effective masses for conduction in the plane of the surface can be complicated functions of k⊥. The mass anisotropies estimated from the cyclotron resonance parameters for the valence band of bulk silicon are in qualitative agreement with the experimental mobility values.
An approximate solution is found of a boundary-value problem arising from the continuity equation in an inhomogeneous semiconductor, leading to rotational current vectors. Results are used to predict the effect of carrier-concentration gradients on magnetoresistance. The predicted weak-field effects are especially significant in degenerate semiconductors and n-type III-V intermetallics where the "intrinsic" magnetoresistance is small. In strong fields, even small gradients in carrier concentration can completely alter the field dependence of the magnetoresistance. Experimental results indicate that transverse currents, which do not occur in the simple case discussed, do appear in general, and further perturb the magnetoresistance. The influence of inhomogeneous magnetic fields is discussed briefly.[This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to ]
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