Efficient spin injection in self-assembled CdSe quantum dots coupled with a diluted magnetic semiconductor quantum well

Electron-spin injection has been studied from a diluted magnetic semiconductor quantum well (DMS-QW) of Zn1–x–yCdxMnySe into self-assembled quantum dots (QDs) of CdSe through a tunneling barrier of ZnSe. The spin injection is experimentally evidenced by time-resolved circularly polarized photoluminescence (PL) in the QDs with the circular polarization degree up to 40%. The fast injection time of 20 ps can be attributed to the tunneling probability of the electron from the DMS-QW side. In addition to this, circularly polarized PL with the lifetime of 3.5 ns is simultaneously observed, indicating type-II transition between the electron in the QDs and the spin-polarized heavy hole in the DMS-QW. Those PL energies directly indicate that the electron tunneling is assisted by a LO phonon in the CdSe QD. The spin injection via LO-phonon-assisted resonant electron tunneling provides an efficient spin-injection process into the self-assembled QD exhibiting strong quantum confinement effects. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)