Spin Injection and Relaxation in Ferromagnet-Semiconductor Heterostructures

TL;DR

This paper investigates spin injection and relaxation mechanisms in Fe/AlGaAs/GaAs heterostructures across a wide temperature range, revealing distinct regimes and temperature-dependent behaviors affecting spin polarization.

Contribution

It provides a comprehensive description of temperature-dependent spin transport and relaxation in ferromagnet-semiconductor heterostructures, highlighting the role of excitons and free electrons.

Findings

Spin polarization depends on temperature regimes and bias conditions.

Maximum spin polarization occurs between 100 and 200 K.

Steady-state spin polarization of at least 6% is observed at room temperature.

Abstract

We present a complete description of spin injection and detection in Fe/Al_xGa_{1-x}As/GaAs heterostructures for temperatures from 2 to 295 K. Measurements of the steady-state spin polarization in the semiconductor indicate three temperature regimes for spin transport and relaxation. At temperatures below 70 K, spin-polarized electrons injected into quantum well structures form excitons, and the spin polarization in the quantum well depends strongly on the electrical bias conditions. At intermediate temperatures, the spin polarization is determined primarily by the spin relaxation rate for free electrons in the quantum well. This process is slow relative to the excitonic spin relaxation rate at lower temperatures and is responsible for a broad maximum in the spin polarization between 100 and 200 K. The spin injection efficiency of the Fe/Al_xGa_{1-x}As Schottky barrier decreases at higher temperatures, although a steady-state spin polarization of at least 6 % is observed at 295 K.