M. K. Welsch

Optical spectroscopy on individual CdSe/ZnMnSe quantum dots

Optical single dot studies in wide-band gap diluted magnetic CdSe/ZnMnSe quantum dots have been performed. Due to the sample design, the photoluminescence energy of the quantum dot signal is energetically below the internal Mn2+ transition, resulting in high quantum efficiencies comparable to nonmagnetic CdSe/ZnSe quantum dots. Magnetic-field- and temperature-dependent measurements on individual dots clearly demonstrate the exchange interaction between single excitons and individual Mn2+ ions, resulting in a giant Zeeman effect and a formation of quasi-zero-dimensional magnetic polarons.

Optical Spectroscopy on Single Semimagnetic Quantum Dots — Probing the Interaction between an Exciton and Its Magnetic Environment

Single diluted magnetic semiconductor (DMS) quantum dots are studied by means of photoluminescence spectroscopy and magnetoluminescence. The sp-d exchange interaction between a single electron-hole pair and roughly 100 Mn spins within the dot is demonstrated to result in (i) a significant enhancement (more than one order of magnitude) of the emission linewidth and (ii) a strongly modified magnetic field dependence of the polarization degree in a single DMS quantum dot as compared to a non-magnetic reference sample.

Selective thermal interdiffusion using patterned SiO2 masks: An alternative approach to buried CdTe/CdMgTe quantum wires

Buried CdTe/CdMgTe quantum wires with a lateral confinement potential of about 290 meV have been realized. Using electron beam lithography, SiO2 stripes are defined on a single quantum well sample and a subsequent 2 h annealing step in a Zn atmosphere results in a surprisingly strong interdiffusion between Cd and Mg atoms under the capped areas, causing a lateral modulation of the band gap. We obtain, e.g., for a nominal wire width of 100 nm, a lateral subband splitting of more than 8 meV, while the extension of the squared exciton wave function of the ground state is reduced to about 20 nm due to the error function-like potential shape.

Photoluminescence spectroscopy on single CdSe quantum dots in a semimagnetic ZnMnSe matrix

Abstract Photoluminescence spectroscopy with high spatial resolution has been applied to study single CdSe quantum dots embedded in a semimagnetic ZnMnSe matrix. The exchange interaction between the exciton and Mn 2+ ions of the crystal matrix results in the formation of a ferromagnetically aligned spin complex, a quasi-0D excitonic magnetic polaron. We demonstrate, that the energy shift of the EMP with temperature and excitation power, respectively, directly reflects the change of the magnetization, in particular the spin temperature, on a nanometer scale.

Semimagnetic (Cd,Mn)Te single quantum dots — technological access and optical spectroscopy

An alternative technological approach for the realization of (Cd,Mn)Te nanostructures is presented. Focused ion beam lithography and subsequent thermal annealing are used for a lateral modulation of the bandgap, allowing both, the realization of quantum wires and quantum dots with adjustable size and a well-defined lateral potential. Due to the high quantum efficiency of the buried nanostructures, photoluminescence spectroscopy even on single quantum dots becomes accessible, allowing an experimental insight on optical transitions in three-dimensionally confined semimagnetic structures.

Optical Spectroscopy on Buried CdTe/Cd(Mn,Mg)Te Single Quantum Dots

Technische Physik, Experimentelle Physik III, Am Hubland, Universita¨t Wu¨rzburg,D-97074 Wu¨rzburg, Germany(Received August 30, 1999)Focused ion beam lithography and subsequent thermal annealing is used to prepare buried CdTe/Cd(Mg,Mn)Te single dots. A well defined lateral potential with a depth of more than 220 meV isachieved, thus exceeding the thermal energy kT at room temperature significantly. The high quan-tum efficiency of the dots allows the investigation of single excitons as well as multiexcitons in thesame single quantum dot.