Spin-polarization dynamics in electrically excited single InGaAs quantum dots

Potential applications of semiconductor quantum dots include spin memory and quantum information processing devices. For these, a rapid spin-initialization process would be desirable. In this contribution, we demonstrate nanosecond-pulsed electrical spin-injection into quantum dots embedded in a spin light-emitting diode. As inferred from time-resolved electroluminescence experiments, the circular polarization degree of the emitted light exhibits a peak at the beginning of the electroluminescence signal, indicating that the spin-initialization is more efficient in pulsed operation than under constant-current excitation. Results for the quantum-dot ensemble, the wetting layer states, and for single quantum dots are presented. We attribute these observations to energy-dependent spin-relaxation processes in the device.