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The spin-dependent tunneling phenomenon in symmetric and asymmetric resonant semiconductor heterostructures is employed in a theoretical study to investigate the output tunnel current polarization at zero magnetic field. A simple model of the resonant tunneling structures and a simple one-electron band approximation with spin-orbit interaction are used in this work. It is shown that asymmetry in the electron distribution at the electrode regions provides spin-polarized tunnel current. An approach to optimize this spin-dependent effect is explored theoretically. In asymmetric resonant tunneling structures, we estimate theoretically that the polarization can reach 40% with a moderate applied electric field.

We present a theoretical study of the effect of the spin-orbit interaction on the electron magnetization and magnetic susceptibility of small semiconductor quantum dots. Those characteristics demonstrate quite interesting behavior at low temperature. The abrupt changes of the magnetization and susceptibility at low magnetic fields are attributed to the alternative crossing between the spin-split electron levels in the energy spectrum, essentially due to the spin-orbit interaction ͑an analog of the general Paschen-Back effect͒. Detailed calculation using parameters of InAs semiconductor quantum dot demonstrates an enhancement of paramagnetism of the dots. There is an additional possibility to control the effect by external electric fields or the dot design.

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In this article we present a unified model for studying the effect of the sizes and shapes of small semiconductor quantum dots on the electron and hole energy states. We solved the three-dimensional effective one band Schrödinger equation for semiconductor quantum dots with disk, lenticular, and conical shapes. For small InAs/GaAs quantum dots we found a substantial difference in the ground state and first excited state electron energies for dots with the same volume but different shapes. Electron energy dependence on volume is found to be quite different from the commonly quoted V Ϫ2/3. The exponent can vary over a wide range and depends on the dot shapes.