Efficient Room-Temperature Operation of a Quantum Dot Spin-Polarized Light-Emitting Diode under High-Bias Conditions

Abstract

Spin-polarized light-emitting diodes (spin LEDs) are essential for the optical transfer of carrier-spin information in spin-based electronic circuits. Efficient operation under high-bias conditions is required for high-speed transfer of spin information and strong light emission. However, achieving high-electroluminescence (EL) circular polarization is hampered by electric-field-induced spin relaxation during drift transport in undoped $\mathrm{Ga}\mathrm{As}$ barriers. Herein, we demonstrate the efficient room-temperature operation of a spin LED using ($\mathrm{In},\mathrm{Ga})\mathrm{As}$ quantum dots (QDs) tunnel coupled with a 5-nm-thick $\mathrm{Ga}(\mathrm{N},\mathrm{As})$ quantum well (QW). A high-EL circular polarization of approximately 7% is achieved, even under high-bias conditions, in comparison with the lower value of approximately 3% for the conventional QD spin LED without $\mathrm{Ga}(\mathrm{N},\mathrm{As})$. This is realized by an increase of spin polarization after injection into the QDs by utilizing remote spin filtering of QD electrons via an adjacent tunnel-coupled $\mathrm{Ga}(\mathrm{N},\mathrm{As})$ QW. These results demonstrate that the tunnel-coupled structure of ($\mathrm{In},\mathrm{Ga})\mathrm{As}$ QDs and $\mathrm{Ga}(\mathrm{N},\mathrm{As})$ QW is a promising active layer of spin LEDs for achieving both strong EL emission and high-EL circular polarization at room temperature.