G. Bacher

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.

Buried single CdTe/CdMnTe quantum dots realized by focused ion beam lithography

Buried single CdTe/CdMnTe quantum dots are realized by implantation-induced intermixing using a focused 100 keV Ga+ ion beam. For an implantation dose of 5×1013 cm−2 and an annealing temperature of 390 °C, a lateral potential depth of about 65 meV is obtained. By means of photoluminescence spectroscopy, the formation of zero-dimensional multiexcitons in single quantum dots is investigated, yielding a biexciton binding energy of about 3.5 meV. In addition, the occurrence of an excited biexciton transition in the photoluminescence spectrum gives clear evidence of a suppressed exciton spin-flip process in quantum dots.

Phonon interaction of single excitons in CdSe/ZnSe quantum dot structures

In epitaxially grown CdSe quantum dots the LO-phonon coupling is studied by analysing phonon-assisted recombination of a single zero-dimensional exciton. Due to the microscopic disorder of Cd-ions the observed line shape of the LO-phonon replica shows an inhomogeneous broadening and cannot be described by a single Lorentzian peaking at one distinct phonon energy. With increasing excitation density, the radiative decay of biexcitons with a binding energy of 22 meV is observed. Both exciton and corresponding biexciton reveal LO-phonon replica intensities of ∼3% of the respective zero-phonon emission.

Phase matched second harmonie generation using a χ(2) modulated ZnTeZnSe optical waveguide

Abstract Second harmonic generation is investigated in a ZnTe ZnSe waveguide structure grown by metalorganic vapour phase epitaxy on (001)GaAs substrate. A focused Ga+-ion beam is used to generate a first order periodic modulation of the nonlinear susceptibility χ(2) within the waveguide. Using a tuneable ps-KTP optical parametric oscillator a clearly enhanced SHG signal is observed at a fundamental wavelength of λF = 1164 nm.

Implantation induced changes in II-VI semiconductor heterostructures

Focused ion beam implantation was used to modulate characteristic optical properties of II-VI heterostructures on a lateral nm-scale. Three different applications will be discussed, including basic physics as well as optoelectronic applications for the visible spectral range. In waveguides based on ZnSe heterostructures, both gain-coupled distributed feedback operation and quasi-phase matched second harmonic generation are investigated by modulating laterally the optical gain and the second order susceptibility χ(2), respectively. In CdTe/CdMnTe quantum wells, bandgap modulation is demonstrated by ion implantation and subsequent rapid thermal annealing, revealing a large potential for realizing semimagnetic nanostructures by selective interdiffusion.