The effects of Schottky barrier profile on spin dependent tunneling in a ferromagnet-insulator-semiconductor system

摘要

The insertion of a tunnel barrier between a ferromagnetic (FM) metal source lead and a semiconductor (SC) layer has proved effective in achieving high spin injection efficiency at the FM-SC interface. We investigate the spin transport across a FM-I (insulator)-SC interface, under the influence of a Schottky barrier which arises in the SC layer close to the interface. The spin transport in the presence of an applied voltage is calculated via the nonequilibrium Green's function (NEGF) tight binding model. The NEGF formalism systematically accounts for: (i) the spatial profile of the Schottky barrier, (ii) the coupling between the FM lead and the SC layer, and (iii) the effect of the entire semi-infinite lead, which can be reduced to a self-energy term. We investigate several parameters (e.g., doping concentration, built-in potential and applied bias) which affect the Schottky barrier profile, and hence the spin current across the FM/I/SC system. It is shown that the spin polarization of current can be significantly improved by having a low Schottky barrier height, but a high built-in potential. A high doping density increases the current density by decreasing the Schottky barrier height and the depletion width, but at the cost of reduced spin polarization.