Search

Abstract: Epitaxial ZnO thin films were grown by pulsed laser deposition (PLD) in N2 or N2O or O2 background gas on MgO-buffered a-plane sapphire. The excitonic room-temperature cathodoluminescence (CL) intensity, the carrier concentration and the Hall mobility showed well-defined maxima for films grown at PLD gas pressures of ca. 1 mbar N2, N2O, and O2. However, despite the comparable high CL intensities of the ZnO films grown in the three different background gases, their surface roughness varied considerably. Films with rough surface showed a broadening and splitting of the room-temperature CL peak into maxima at 3.21 and 3.26 eV, which could be due to either grain morphology or spatial variation of the electronic defect structure. [Copyright &y& Elsevier]

Abstract: Free-standing, two-dimensional ZnO nanosheets and branched honeycomb-like nanowalls have been grown together with one-dimensional nanothreads on gold covered a-plane sapphire and GaN templates on silicon substrates using Al2O3 assisted carbothermal evaporation of ZnO. In X-ray diffraction 2Θ−ω scans two orientations, ZnO(0001) and ZnO(10-11), of the two-dimensional nanosheets were detected. Temperature dependent cathodoluminescence shows bound exciton and donor–acceptor pair recombinations with a linewidth of 2.1 meV at 10 K. We show that the formation of the novel Al-doped ZnO nanostructures is due a vapor–liquid–solid mechanism. [Copyright &y& Elsevier]

Abstract: Electrical and polarization hysteresis measurements on Pt–BaTiO3–ZnO–Pt heterostructures, grown by pulsed laser deposition on (001)Si, are reported. The layers were deposited without breaking the vacuum using a switchable target holder. Offsets of hysteresis loops along the polarization axis with increasing sweeping voltage, time-dependent charging, and rectifying behavior are observed. A simple electrical circuitry can be used to model the observed hysteresis behavior, where the interface between the wurtzite-structure ZnO and the pervoskite-structure BaTiO3 is seen as the origin of a space charge accumulation region. Coupling between spontaneous wurtzite and switchable ferroelectric polarization is discussed. [Copyright &y& Elsevier]

a-Si/SiO x Bragg-reflectors for the wavelength region from 500 nm to 830 nm with a low number of pairs were grown on cylindrical half-pipes on InP substrates using plasma-enhanced chemical vapor deposition with regard to applications for the confinement of the optical modes in micro-resonators. The optical properties of the Bragg-reflectors were determined by the new method of detection-focal spatially resolved spectroscopic ellipsometry in combination with the confocal micro-reflection technique. [Copyright &y& Elsevier]

The ordinary optical dielectric functions of pulsed-laser-deposition grown wurtzite c-plane MgxZn1−xO (0≤x≤0.53) thin films have been determined by using spectroscopic ellipsometry in the photon energy range from 4.5 to 9.5 eV. The dielectric functions reveal features which resemble those previously detected in uniaxial AlGaN and identified as E1- and E2-type band-to-band transitions with no remarkable dependence of the transition energy on Mg content x. The E1- and E2-type transitions for ZnO are compared with pseudopotential band-structure calculations. [Copyright &y& Elsevier]

Abstract: We report electro-optical measurements of BaTiO3/ZnO heterostructures grown by pulsed laser deposition. The optical properties of the heterostructures were examined with and without an applied bias. A change in the heterostructure optical properties is found and attributed to a linear electro-optical effect causing a change in the band gap. Moreover the formation of an electric polarization in the BaTiO3 layer causes a remanent change in the dielectric function if the bias is removed. The change could be estimated to be around 5meV. [Copyright &y& Elsevier]