J. Geurts

Secondary phase segregation in heavily transition metal implanted ZnO

With micro-Raman spectroscopy and x-ray diffraction (XRD), we studied ZnO crystals implanted with Mn, Fe, Co, and Ni, respectively, with implantation concentrations from 4 up to 16u2002at.u2009%. Using thermal treatments in air up to 700u2009°C, we analyzed the annealing effect on the ZnO crystal lattice as well as the onset of secondary phases and their microstructure on the sample surface. While the 500u2009°C treatment induces a considerable annealing, secondary phases are observed for transition metal (TM) concentrations ≥8u2002at.u2009% after the treatment at 700u2009°C. Their microstructure strongly depends on the TM species. Various stoichiometric and nonstoichiometric TM oxide precipitates as well as elemental TM clusters are identified by their Raman and XRD signatures and their possible magnetic impact is discussed.

Raman identification of the in-plane axes of zincblende (100) surfaces: Basic principles and application to II–VI/III–V heterostructures

We use the interference of deformation-potential- and Frohlich-induced Raman scattering from LO phonons in zincblende materials to identify the in-plane axes of zincblende (100) surfaces and interfaces. This procedure, which allows e.g. to distinguish between the [011] and the [0–11] direction, is demonstrated experimentally for n- and p-type GaAs(100). The main potential of the method is its application to heterostructures. Here it allows the unambiguous assignment of polarized Raman scattering features from surfaces and interfaces to their characteristic symmetry directions. Two examples are presented: (i) localized vibrations of CdSe monolayers, embedded in BeTe stacks, and (ii) vibration modes of Te dimers on clean (2×1) reconstructed BeTe(100) surfaces.