Longitudinal spin-relaxation of donor-bound electrons in direct bandgap semiconductors

TL;DR

This study measures and analyzes the longitudinal spin-relaxation times of donor-bound electrons in GaAs, InP, and CdTe, revealing magnetic field-dependent mechanisms and theoretical insights into spin-phonon interactions.

Contribution

It provides the first comprehensive measurement of $T_1$ in these semiconductors and compares experimental results with theory, highlighting the importance of spin-phonon interactions at high fields.

Findings

Maximum $T_1$ observed: 1.4 ms in GaAs, 0.4 ms in InP, 1.2 ms in CdTe.

Low-field relaxation is density and temperature dependent, dominated by hyperfine interactions.

High-field relaxation follows a power-law dependence with exponent 3 to 4.

Abstract

We measure the donor-bound electron longitudinal spin-relaxation time ($T_1$) as a function of magnetic field ($B$) in three high-purity direct-bandgap semiconductors: GaAs, InP, and CdTe, observing a maximum $T_1$ of $1.4~\text{ms}$, $0.4~\text{ms}$ and $1.2~\text{ms}$, respectively. In GaAs and InP at low magnetic field, up to $\sim2~\text{T}$, the spin-relaxation mechanism is strongly density and temperature dependent and is attributed to the random precession of the electron spin in hyperfine fields caused by the lattice nuclear spins. In all three semiconductors at high magnetic field, we observe a power-law dependence ${T_1 \propto B^{-\nu}}$ with ${3\lesssim \nu \lesssim 4}$. Our theory predicts that the direct spin-phonon interaction is important in all three materials in this regime in contrast to quantum dot structures. In addition, the "admixture" mechanism caused by Dresselhaus spin-orbit coupling combined with single-phonon processes has a comparable contribution in GaAs. We find excellent agreement between high-field theory and experiment for GaAs and CdTe with no free parameters, however a significant discrepancy exists for InP.