Spin-polarized resonant transport in a hybrid ferromagnetic–two-dimensional electron gas structure

Abstract

We investigated the spin-polarized resonant transport in a hybrid high-electron-mobility transistor (HEMT) structure, with source and drain electrodes made of ferromagnetic (FM) material, while the channel consists of a highly doped ${n}^{++}$ AlGaAs-GaAs two-dimensional electron gas (2DEG). The electron transport in the FM layer is modeled using the spin-drift diffusion model, while across the 2DEG layer, ballistic transport is assumed, given the long mean free path within the 2DEG. By solving the two transport models self-consistently, we found that the transport properties of the device, such as the transmission probability, the spin injection (SI) efficiency, and the magnetoresistance (MR) ratio, all exhibit oscillatory behavior when the 2DEG layer width or the 2DEG Fermi energy is varied. The basis of these oscillations is the resonant transport across the 2DEG, which is reminiscent of the spin-polarized resonant tunneling (SPRT), observed recently in magnetic tunnel junctions (MTJs). The hybrid device has distinct advantages over the metal-based MTJ structures in the practical utilization of the SPRT effect. This is because the ballistic charge conduction through the 2DEG enables easy tunability of the MR ratio and SI efficiency, by varying the doping density and gate bias, while avoiding the exponential suppression of MR with barrier thickness, which occurs in MTJ devices. Numerically, the hybrid HEMT device is predicted to be capable of achieving maximum MR and SI ratios approaching 20% and 40%, respectively, at the crest of their respective oscillations.