Electrical spin injection into single InGaAs quantum dots

Abstract

In the context of a potential future quantum information processing we investigate the concurrent initialization of electronic spin states in InGaAs quantum dots (QDs) via electrical injection from ZnMn(S)Se spin aligners. Single dots can be read out optically through metallic apertures on top of our spin-injection light-emitting diodes (spin-LEDs). A reproducible spin polarization degree close to 100% is observed for a subset of the QD ensemble. However, the average polarization degree is lower and drops with increasing QD emission wavelength. Our measurements suggest that spin relaxation processes outside the QDs, related to the energetic position of the electron quasi-Fermi level, as well as defect-related spin scattering at the III-V/II-VI interface should be responsible for this effect, leading us to an improved device design. Finally, we present first time-resolved electroluminescence measurements of the polarization dynamics using ns-pulsed electrical excitation. The latter should not only enable us to gain a more detailed understanding of the spin and carrier relaxation processes in our devices. They are also the first step towards future time-resolved optical and electrical spin manipulation experiments. © 2009 Springer-Verlag Berlin Heidelberg.