Bias-dependent electron spin lifetimes in n-GaAs and the role of donor impact ionization

TL;DR

This study investigates how electron spin lifetimes in n-GaAs change with applied electric bias, revealing a sharp decrease at the donor impact ionization threshold due to increased delocalized electrons affecting spin relaxation.

Contribution

It demonstrates the bias-dependent collapse of spin lifetime linked to donor impact ionization and delocalized electron dynamics in n-GaAs near the metal-insulator transition.

Findings

Spin lifetime exceeds 100 ns at low bias and low temperature.

A sharp decrease in spin lifetime occurs above 10 V/cm bias.

Donor impact ionization increases delocalized electrons, affecting spin relaxation.

Abstract

In bulk n-GaAs epilayers doped near the metal-insulator transition, we study the evolution of electron spin lifetime $\tau_s$ as a function of applied lateral electrical bias $E_x$. $\tau_s$ is measured via the Hanle effect using magneto-optical Kerr rotation. At low temperatures (T<10 K, where electrons are partially localized and $\tau_s > 100$ ns at zero bias), a marked collapse of $\tau_s$ is observed when $E_x$ exceeds the donor impact ionization threshold at $\sim$10 V/cm. A steep increase in the concentration of warm delocalized electrons -- subject to Dyakonov-Perel spin relaxation -- accounts for the rapid collapse of $\tau_s$, and strongly influences electron spin transport in this regime.