H. Alves

Nitrogen-related local vibrational modes in ZnO:N

We study the influence of nitrogen, a potential acceptor in ZnO, on the lattice dynamics of ZnO. A series of samples grown by chemical vapor deposition (CVD) containing different nitrogen concentrations, as determined by secondary ion mass spectroscopy (SIMS), was investigated. The Raman spectra revealed vibrational modes at 275, 510, 582, 643, and 856 cm−1 in addition to the host phonons of ZnO. The intensity of these additional modes correlates linearly with the nitrogen concentration and can be used as a quantitative measure of nitrogen in ZnO. These modes are interpreted as local vibrational modes. Furthermore, SIMS showed a correlation between the concentration of incorporated nitrogen and unintentional hydrogen, similar to the incorporation of the p-dopant magnesium and hydrogen in GaN during metalorganic CVD.

Behind the weak excitonic emission of ZnO quantum dots: ZnO/Zn(OH)2 core-shell structure

The structure of ZnO quantum dots prepared via the wet chemical method was studied. By introducing an annealing treatment (150 °C–500 °C), we also investigated the effect of the change in the structure of the dots on their luminescence properties. Our studies revealed that the surface of the as-prepared dots is passivated by a thin layer of Zn(OH)2, thus, the dots consist of a ZnO/Zn(OH)2 core-shell structure. We present evidence that the weak excitonic transition of ZnO quantum dots is strongly correlated with the presence of the surface shell of Zn(OH)2. When Zn(OH)2 is present, the excitonic transition is quenched.

Structural and optical properties of epitaxial and bulk ZnO

In this letter, we compare the properties of bulk and epitaxial ZnO. The ZnO thin films were grown on GaN templates and on ZnO single crystals by vapor phase deposition using Zn and NO2 as precursors. We use high-resolution x-ray diffraction to resolve the structural properties. The rocking curves of the bulk crystal are extremely broad caused by a mosaic structure of the substrate. The homoepitaxial ZnO film mimics the properties of the ZnO substrate whereas ZnO films on GaN templates showed superior rocking curve half width as small as 230 arcsec. The optical properties are investigated by temperature-dependent photoluminescence. Different donor and acceptor bound excitons can be distinguished for a half width of the recombination lines less than 1 meV. Free exciton emission is already detectable at liquid-He temperatures proofing the high quality of the epitaxial films.

Optical investigations on excitons bound to impurities and dislocations in ZnO

Abstract The optical properties of excitonic recombinations in bulk ZnO are investigated by photoluminescence (PL) measurements. At liquid helium temperature the neutral donor bound excitons are positioned at 3.364, 3.362 and 3.361 eV, the line at 3.364 eV dominates the PL spectra. Annealing of the crystals demonstrates that the 3.364 eV vanishes, it is most likely caused by the hydrogen related donor. Two-electron satellite transitions of the donor bound excitons allow to determine the donor binding energies to 43, 52 and 55 meV. These results are in line with the temperature dependent Hall effect measurements. In the as-grown crystals two donors with binding energies of 30 and 50 meV control the conductivity, whereas after annealing only one donor with a binding energy of about 50 meV is necessary to fit the data perfectly. In addition at 3.335 eV an excitonic recombination is observed, which supported by spatially resolved cathodoluminescence measurements, is attributed to excitons bound to structural defects.

Magneto-optical properties of bound excitons in ZnO

We present results of magneto-optical measurements and theoretical analysis of shallow bound exciton complexes in bulk ZnO. Polarization and angular dependencies of magnetophotoluminescence spectra at 5 T suggest that the upper valence band has

The Red (1.8 eV) Luminescence in Epitaxially Grown GaN

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Correlation of Mn local structure and photoluminescence from CdS:Mn nanoparticles

symmetry. Nitrogen doping leads to the formation of an acceptor center that compensates shallow donors. This is confirmed by the observation of excitons bound to ionized donors in nitrogen doped ZnO. The strongest transition in the ZnO:N

Effect of the (OH) Surface Capping on ZnO Quantum Dots

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Dislocation reduction in GaN grown by hydride vapor phase epitaxy via growth interruption modulation

transition) is associated with a donor bound exciton. This conclusion is based on its thermalization behavior in temperature-dependent magnetotransmission measurements and is supported by comparison of the thermalization properties of the

Defects and defect identification in group III-nitrides

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