The spin-dependent tunneling phenomenon in symmetric and asymmetric semiconductor heterostructures at zero magnetic field is studied theoretically on the base of a single conduction band and spin-dependent boundary conditions approach. It is shown that the spin-orbit splitting in the dispersion relation for the electrons in A III B V semiconductor quantum-tunneling structures can provide a dependence of the tunneling transmission probability on the electron's spin polarization. The dependence is calculated and discussed for different kinds of tunnel heterostructures.

Spin-dependent tunneling in symmetric and asymmetric double-barrier semiconductor heterostructures is studied. The effective one-band Hamiltonian approximation and spin-dependent boundary conditions approach are used for a theoretical investigation of the influence of electron spin on the tunneling probability. It is shown that spin-orbit splitting in the dispersion relation for electrons in A III B V semiconductors can provide the dependence of the tunneling transmission probability on the electron-spin polarization without additional magnetic field. The dependence can be controlled by an external electric field, and may be significant for realistic models of double-barrier semiconductor heterostructures. ͓S0163-1829͑99͒02320-6͔

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.

Multiple quantum well infrared photodetectors (QWIPs) with bi-periodic grating couplers have been demonstrated. The bi-periodic grating consists of two gratings with different periods. The response linewidths of such QWIPs are found to be much wider than those of conventional grating coupled QWIPs. By using bi-periodic gratings for coupling the radiation into QWIPs, the influence of variation of material and grating quality on the performance of QWIP can be largely eliminated.