Spin-injection and spin-relaxation in p-doped InGaAs/GaAs quantum-dot spin light emitting diode at zero magnetic field

TL;DR

This study demonstrates efficient spin injection and analyzes spin relaxation mechanisms in p-doped InGaAs/GaAs quantum-dot spin LEDs at zero magnetic field, achieving notable polarization up to 100K and elucidating two-step relaxation processes.

Contribution

It introduces a high-efficiency spin injection method in quantum-dot LEDs at zero magnetic field and details the two-step spin relaxation mechanisms affecting polarization.

Findings

Achieved ~19% electroluminescence circular polarization at 100K.

Identified two-step spin relaxation process involving tunneling and quantum dot capture.

Demonstrated bias and temperature dependence of spin polarization.

Abstract

We report on efficient spin injection in p-doped InGaAs/GaAs quantum-dot (QD) spin light emitting diode (spin-LED) under zero applied magnetic field. A high degree of electroluminescence circular polarization (Pc) ~19% is measured in remanence up to 100K. This result is obtained thanks to the combination of a perpendicularly magnetized CoFeB/MgO spin injector allowing efficient spin injection and an appropriate p-doped InGaAs/GaAs QD layer in the active region. By analyzing the bias and temperature dependence of the electroluminescence circular polarization, we have evidenced a two-step spin relaxation process. The first step occurs when electrons tunnel through the MgO barrier and travel across the GaAs depletion layer. The spin relaxation is dominated by the Dyakonov-Perel mechanism related to the kinetic energy of electrons, which is characterized by a bias dependent Pc. The second step occurs when electrons are captured into QDs prior to their radiative recombination with holes. The temperature dependence of Pc reflects the temperature induced modification of the QDs doping, together with the variation of the ratio between the charge carrier lifetime and the spin relaxation time inside the QDs. The understanding of these spin relaxation mechanisms is essential to improve the performance of spin LED for future spin optoelectronic applications at room temperature under zero applied magnetic field.