Search results for "Wurtzite crystal structure"
showing 10 items of 87 documents
Electronic and optical properties of InN nanowires
2016
Abstract We have employed a multiband envelope function method to study wurtzite [0001] InN nanowires of cylindrical cross section. The electronic subband structure and optical absorption spectrum are calculated as a function of the nanowire radius. The energies of the Γ -point conduction band states show a monotonous increase with decreasing radius. On the other hand, the size dispersion of the valence band states is more involved, showing various crossing and anticrossing effects due to the interplay between the confinement and band mixing effects. Thus, for small ( R 2 nm ) nanowires the highest valence band state has dominant p z -symmetry, but for R > 2 nm the highest state has dominan…
Structural, electrical and optical properties of zinc‐iridium oxide thin films deposited by DC reactive magnetron sputtering
2014
ZnO-IrO2 thin films were deposited on glass by DC reactive magnetron sputtering at room tem-perature. Structural, electrical and optical properties were investigated as a function of iridium atomic concentra-tion in the films. XRD data shows that ZnO-IrO2 thin films are X-ray amorphous and Raman spectrum resembles the spectrum of IrO2, without any distinct features of wurtzite ZnO structure. The lowest film resistivity and the highest transmittance achieved in the present study were 1.4 × 10-3 Ωcm and 33% at 550 nm, respectively. However, resistivity and transmittance are inversely related to the iridium concentration in the films.
Raman, electron microscopy and electrical transport studies of x-ray amorphous Zn-Ir-O thin films deposited by reactive DC magnetron sputtering
2015
Zn-Ir-O thin films on glass and Ti substrates were deposited by reactive DC magnetron sputtering at room temperature. Structural and electrical properties were investigated as a function of iridium concentration in the films. Raman spectrum of Zn-Ir-O (61.5 at.% Ir) resembles the spectrum of rutile IrO2, without any distinct features of wurtzite ZnO structure. SEM images indicated that morphology of the films surface improves with the iridium content. EDX spectroscopy and cross-section SEM images revealed that the films growing process is homogeneous. Crystallites with approximately 2-5 nm size were discovered in the TEM images. Thermally activated conductivity related to the variable range…
Optical and magnetic properties of ZnCoO thin films synthesized by electrodeposition
2008
Ternary Zn1−xCoxO crystalline films with different compositions were grown by electrodeposition. The Co content in the final compound is linked to the initial Co/Zn ratio in the starting solution. X-ray diffraction reveals a wurtzite structure for the Zn1−xCoxO films. Transmittance spectra show two effects proportional to Co content, a redshift of the absorption edge and three absorption bands, which are both interpreted to be due to the Co incorporated into the ZnO lattice. The amount of deposited charge was used to get a precise control of the film thickness. Magnetic measurements point out that Co(II) ions are isolated from each other, and consequently the films are paramagnetic. Francis…
Optical properties of wurtzite and rock-salt ZnO under pressure
2005
Abstract This paper reports on the pressure dependence of the optical absorption edge of ZnO in the wurtzite and rock-salt phase, up to 14 GPa. Both vapor-phase monocrystals and pulsed-laser-deposition thin films have been investigated. In both types of samples the wurtzite to rock-salt transition is observed at 9.7±0.2 GPa. The absorption tail of the fundamental gap, as measured in monocrystals, exhibits a pressure coefficient of 24.5±2 meV/GPa. The evolution under pressure of the full absorption edge of the wurtzite phase is studied with thin film samples, yielding a slightly lower pressure coefficient (23.0±0.5 meV/GPa for the A–B exciton). Rock-salt ZnO is shown to be an indirect semico…
Phonon Dispersion of Wurtzite CdSe: The Bond Charge Model
2000
The phonon dispersion of wurtzite CdSe is presented along the main directions of the Brillouin zone. The study has been performed by using a bond charge model for wurtzite-type semiconductors with only six adjustable parameters. The results are compared against neutron scattering data and ab initio calculations. The phonon eigenvectors corresponding to the vibrational modes at the Γ-point are in very good agreement with the ab initio calculations.
Local structure and magnetization of ferromagnetic Cu-doped ZnO films: No magnetism at the dopant?
2016
Abstract Relationship between magnetism and structure of Cu-doped ZnO was investigated at macroscopic and microscopic levels. Thin Zn1−xCuxO films (x = 0.02, 0.04, 0.07 and 0.10) were prepared by a pulsed laser deposition and characterized via superconducting quantum interference device (SQUID) magnetometry, high-resolution x-ray diffraction, and Cu K-edge and Zn K-edge x-ray absorption, x-ray linear dichroism and x-ray circular magnetic dichroism spectroscopy. Even though the samples exhibit room-temperature ferromagnetism with magnetization that increases with Cu concentration, we did not detect signatures of local magnetic moments associated with Cu atoms, as evidenced by the lack of any…
Review on Raman scattering in semiconductor nanowires: I. theory
2013
Raman scattering is a nondestructive technique that is able to supply information on the crystal and electronic structures, strain, temperature, phonon-phonon, and electron-phonon interaction. In the particular case of semiconductor nanowires, Raman scattering provides addi- tional information related to surfaces. Although correct, a theoretical approach to analyze the surface optical modes loses critical information when retardation is neglected. A comparison of the retarded and unretarded approaches clarifies the role of the electric and magnetic polarization in the Raman selection rules. Since most III-V compounds growing in the zincblende phase change their crystal structure to wurtzite…
Phonon dispersion in GaN/AlN non‐polar quantum wells: confinement and anisotropy
2007
We have calculated the phonon dispersion relations in a non-polar GaN/AlN quantum well within the dielectric continuum model and making use of Loudon's model of uniaxial crystals. Due to the strong in-plane anisotropy of this orientation, we have found that in general ordinary and extraordinary phonons are not decoupled. In this work we analyze the conditions for the occurrence of interface modes. In these novel heterostructures there is an added dependence of the phonon dispersion on the orientation of the in-plane phonon wavevector, which allows the existence of interface phonons at energies forbidden in the better known polar structures. Under particular circumstances the vibrations exci…
Quantum chemical simulations of doped ZnO nanowires for photocatalytic hydrogen generation
2016
Zinc oxide (ZnO) is considered in general as a promising material for solar water splitting. Its wurtzite-structured bulk samples, however, can be considered as active for photocatalytic applications only under UV irradiation, where they possess ∼1% efficiency of sunlight energy conversion due to their wide band gap (3.4 eV). Although pristine ZnO nanowires (NWs) possess noticeably narrower band gaps than the bulk, the tendency of band gap reduction with increasing NW diameter is insufficient, and further modification is required. We have contributed to filling this gap by performing a series of ab initio calculations on ZnO NWs of different diameters (dNW), which are mono-doped by metal (A…