Theoretical methods for spintronics in semiconductors with applications

Abstract

Theoretical studies of the role of structural inversion symmetry (SIA) and bulk inversion symmetry (BIA) in the band structure and tunneling properties of zincblende heterostructures have been carried out. The effective bond orbital model (EBOM) method is used to examine the spin splitting due to SIA in AlSb/InAs/GaSb asymmetric heterostructures. It is found for the resulting two-dimensional electron gas (2DEG) that large theoretical values of the Rashba coefficient in the range of 50E-10 eV.cm can be achieved for optimized structures. Structures presenting anticrossing of the conduction and valence bands show an appreciable reduction in the value of the Rashba coefficient. The possibility of extracting the Rashba coefficient from magnetization measurements is explored. An expression is derived, valid in the diffusive limit, for the spin polarization of the current resulting from a bias parallel to the plane of the quantum well. The EBOM method is expanded to include BIA effects. The resulting formalism is then used to compute the band structure of an AlSb/GaSb superlattice, where the BIA-induced splitting is observed. The results agree with k.p calculations. The first implementation of an 8-band Envelope Function Approximation method faithful to the T_d symmetry of bulk zincblendes has been made. It has been used to compute the bands for quantum wells with and without BIA effects included, and demonstrates that the BIA effects can be of the same order of magnitude as SIA (i.e., Rashba) effects. A 2-band Hamiltonian describing BIA effects is proposed. The origin of spurious solutions for certain values of the input parameters is determined and a condition for its absence is derived. Modest modifications to the superlattice method allow the computation of spin-dependent transmission coefficients with the multiband quantum transmitting boundary method (MQTBM). The effect of BIA on the transmitted states and the spin filtering action of an asymmetric resonant interband tunneling diode are investigated. Finally, a Monte Carlo single photon generation algorithm is devised. The photons generated are satisfactory for simulation of light emitted from band-to-band spontaneous transitions in crystals. The polarization is determined taking into account the electron spin, making the algorithm suitable for the analysis of optical detection of spin injection experiments.