Spin diffusion in doped semiconductors

TL;DR

This paper investigates how spin diffusion behaves differently in doped semiconductors compared to intrinsic ones, revealing significant enhancements and polarization-dependent effects in various doping and magnetic conditions.

Contribution

It demonstrates that doped semiconductors allow for single-band spin disturbances with enhanced diffusion, and predicts polarization-dependent spin packet velocities in magnetic semiconductors.

Findings

Spin diffusion is qualitatively different in doped vs. intrinsic semiconductors.

Degenerate electron seas significantly enhance spin diffusion in n-doped semiconductors.

Spin packet velocities depend on polarization and doping type, with notable differences in magnetic semiconductors.

Abstract

The behavior of spin diffusion in doped semiconductors is shown to be qualitatively different than in undoped (intrinsic) ones. Whereas a spin packet in an intrinsic semiconductor must be a multiple-band disturbance, involving inhomogeneous distributions of both electrons and holes, in a doped semiconductor a single-band disturbance is possible. For n-doped nonmagnetic semiconductors the enhancement of diffusion due to a degenerate electron sea in the conduction band is much larger for these single-band spin packets than for charge packets, and can exceed an order of magnitude at low temperatures even for equilibrium dopings as small as 10^16 cm^-3. In n-doped ferromagnetic and semimagnetic semiconductors the motion of spin packets polarized antiparallel to the equilibrium carrier spin polarization is predicted to be an order of magnitude faster than for parallel polarized spin packets. These results are reversed for p-doped semiconductors.