Nonlinear electron and spin transport in semiconductor superlattices

TL;DR

This paper develops a kinetic model for nonlinear charge and spin transport in semiconductor superlattices, deriving drift-diffusion equations and demonstrating stable current and spin oscillations through numerical simulations.

Contribution

It introduces a Chapman-Enskog based derivation of nonlocal drift-diffusion equations for miniband populations and electric fields, including spin effects, in superlattices.

Findings

Stable self-sustained current oscillations observed.

Spin polarization oscillations demonstrated.

Model captures nonlinear electron and spin dynamics.

Abstract

Nonlinear charge transport in strongly coupled semiconductor superlattices is described by Wigner-Poisson kinetic equations involving one or two minibands. Electron-electron collisions are treated within the Hartree approximation whereas other inelastic collisions are described by a modified BGK (Bhatnaghar-Gross-Krook) model. The hyperbolic limit is such that the collision frequencies are of the same order as the Bloch frequencies due to the electric field and the corresponding terms in the kinetic equation are dominant. In this limit, spatially nonlocal drift-diffusion balance equations for the miniband populations and the electric field are derived by means of the Chapman-Enskog perturbation technique. For a lateral superlattice with spin-orbit interaction, electrons with spin up or down have different energies and their corresponding drift-diffusion equations can be used to calculate spin-polarized currents and electron spin polarization. Numerical solutions show stable self-sustained oscillations of the current and the spin polarization through a voltage biased lateral superlattice thereby providing an example of superlattice spin oscillator.