Electrical Spin Injection into InGaAs Quantum Dots

Abstract

The electrical injection of spin-polarized electrons from ferromagnetic Fe contacts into self-assembled InGaAs quantum dots (QDs) incorporated in GaAs/AlGaAs spin light-emitting diode (spin-LED) structures is summarized here. The emissions from the ensemble QDs are efficient and broad in energy due to inhomogeneous broadening (QD size distribution). The circular polarization was measured as functions of current, magnetic field, and temperature. Electrical spin injection at room temperature was achieved, and the spin polarization of the QD emission was found to be remarkably insensitive to temperature. Robust spin polarization was also found in the emission from the InAs wetting layer (WL). At low temperatures, a sharp drop in QD polarization at fields around 5 T is observed, attributed to an efficient magnetic field-induced spin relaxation mechanism involving a two-step process when the dots are occupied by three electron-hole pairs. A modified growth method was also employed to produce low-density and high-uniformity dots to study the spin population of individual shell states. Sequential filling of the s-, p-, d-, and f-shells and the control of their polarization were demonstrated using a spinpolarized current from the Fe contact, and the s-p and p-d intershell exchange energies were determined. These results demonstrate that the spin polarization in InGaAs QDs is robust and can be controlled by a spin-polarized electrical current, an important step toward utilizing QDs in next-generation devices for information processing. List of Abbreviations 2DEG2-dimensional electron gas