Journal of the Korean Physical Society, Vol. 42, No. 6, June 2003, pp. 795∼798 Magneto-Photoluminescence and Spin Dynamics of Self-Assembled CdSe Quantum Dots in Zn 1-x Mn x Se Eunsoon Oh, * S. M. Soh, J. U. Lee, K. J. Yee, J. C. Woo, H. S. Jeon and D. S. Kim BK21 Physics Research Division, Seoul National University, Seoul 151-742 S. Lee Department of Physics, Korea University, Seoul 151-742 J. K. Furdyna Department of Physics, University of Notre Dame, South Bend, Indiana, U.S.A. H. C. Ri, H. S. Chany and S. H. Park Korea Basic Research Institute, Daejon 305-333 (Received 7 February 2003) We have studied photoluminescence spectra of CdSe self-assembled quantum dots (QD’s) em- bedded in Zn1-xMnxSe (x = 0.05 and 0.15) with and without an external magnetic field. Under a magnetic field, the photoluminescence from CdSe QD’s was circularly polarized under light excita- tion above the bandgap energy of ZnMnSe, indicating carrier spin polarization in CdSe QD’s. The time-resolved photoluminescence study showed that spin-flip occured very rapidly as photocarriers transfered from the ZnMnSe to the CdSe QD’s to reach statistical equilibrium of the spin states in the CdSe QD’s. The Zeeman splitting in the CdSe QD’s was several meV, still larger than the thermal energy at 5 K. These results suggest that the spin-polarization in CdSe QD’s is mainly due to the Zeeman splitting of carriers in the CdSe quantum dots. PACS numbers: 75 Keywords: Spin polarization, Magnetic semiconductor, Quantum dot, Photoluminescence I. INTRODUCTION In magnetic semiconductors, electrons and holes ex- perience large spin splitting due to the large exchange interaction between the band carriers and magnetic ions [1, 2]. The spin splitting energy can be measured from the redshift of the luminescence or from the Raman shift associated with spin flip of electrons in the presence of an external magnetic field [3,4]. When the spin splitting is sufficiently larger than the thermal energy, most carriers will relax to the lower energy spin state. Spin polarized carriers in non-magnetic quantum wells can be obtained by injecting the spin-polarized carriers from magnetic semiconductors and has been demonstrated using II-VI and III-V magnetic semiconductors, Zn 1-x Mn x Se [5, 6] and Ga 1-x Mn x As [7]. In multiple quantum well struc- tures whose barriers consist of magnetic semiconductors (e.g., Zn 1-y Cd y Se/Zn 1-x Mn x Se), significant redshifts of * E-mail: esoh@cnu.ac.kr; Present address: Dept. of Phys., Chungnam Nat’l Univ., Daejon 305-764 the luminescence have been observed in magnetic fields due to wavefunction penetration of carriers into the mag- netic barriers [8]. Spin states in quantum dots (QD’s) are of interest for single electron transistors [9] and quantum computing [10]; thus, the spin-polarization and spin dynamics stud- ies in semiconductor QD’s are important. A QD system embedded in magnetic semiconductors provides a nice opportunity to manipulate spin states by using magnetic fields. Spin-polarization studies of quantum dots sur- rounded by magnetic semiconductors are relatively rare, probably because such quantum dots have low lumines- cence efficiency due to the fast energy transfer from car- riers to the localized electrons in the magnetic ions, such as the 3d electrons in the Mn 2+ shell. In this paper, we discuss the magneto-photolumine- scence spectra of self-assembled CdSe QD’s embed- ded in the II-VI magnetic semiconductor Zn 1-x Mn x Se and show that almost perfect spin polarization can be achieved in the QD’s. Under light excitation above the bandgap of ZnMnSe, photocarriers are created in the Zn- MnSe, and they will have statistical distribution of spin -795-