7 research outputs found

    Blueshift in MgxZn1-xO alloys: nature of bandgap bowing

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    A Mg composition-dependent blueshift has been studied in MgxZn1−xO alloys deposited on 6H-SiC(0001) substrates. The localized exciton energy in MgxZn1−xO alloys for x ∼ 0.3 was blueshifted in the range 212–248 meV. The large negative bowing parameter was estimated in MgxZn1−xO alloys to be 4.72±0.84 eV. This large bandgap bowing emphasizes the Stokes shift, which has been attributed to the existence of spontaneous polarization effects due to the polar growth of MgxZn1−xO/SiC heterostructure and local compositional inhomogeneity

    Pulsed laser deposited stoichiometric ZnO thin films

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    Room temperature free-exciton emission was observed in stoichiometric ZnO epilayers grown on Al2O3 substrates by pulsed laser deposition. Absorption and photoluminescence measurements clearly showed the free- exciton emissions at 3.30∼3.31 eV. This fre

    Stoichiometry enhanced exciton-phonon interactions in ZnO epilayers

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    Stoichiometry enhanced exciton-phonon couplings have been studied in ZnO epilayers grown on Al2O3 substrates by pulsed laser deposition. Rutherford backscattering spectroscopy indicated the stoichiometry, while clear hexagonal morphology revealed the Zn-polar growth of ZnO epilayers. From these high-quality and single-crystalline ZnO epilayers free-exciton emissions were observed at 3.30-3.31 eV with a low resistivity of ≤10 -2 Ω cm. Theoretical models were considered for fitting the experimental data to estimate the exciton-phonon interactions in ZnO epilayers. The enhanced exciton-phonon coupling, effective phonon energy and electron-phonon interaction were found to be 680 meV, 65.5 meV and 0.093 meV K-1, respectively. These larger interactions between excitons and phonons even with the lattice dilation have been attributed to the higher Fröhlich constant due to the strong localization energy in the stoichiometric ZnO epilayers

    ZnO Nanostructures: Synthesis and Properties

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    Heterointerfaces of stable and metastable ZnO phases

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    Thermodynamically ZnO is a prototype material which stabilizes with stable and metastable wurtzite and zincblende phases. In principle, the phase stability of ZnO depends on many parameters; however, heterointerface plays a significant role in controlling the ZnO crystalline structures. ZnO/SiC and ZnO/ZnS heterointerfaces have been studied where ZnO layers grow along the out-of-plane with an epitaxial relationship of (0 0 0 1)ZnO∥(0 0 01)SiC, [ 1 1 over(2, ̄) 0 ]ZnO ∥ [ 1 1 over(2, ̄) 0 ]SiC and [1 1 0]ZnO∥[1 1 0]GaAs, [ 1 over(1, ̄) 0 ]ZnO ∥ [ 1 over(1, ̄) 0 ]GaAs, respectively. Although both the ZnO phases grew uniaxially with the substrates, thin-interlayer and imbalanced charge distribution were observed in the ZnO/SiC heterointerfaces, while the ZnO/GaAs heterointerface was dominant with stacking faults and phase coexistence in lattice matrix, together with the common misfit-dislocations. Photoluminescence showed a significant bandgap energy difference in ZnO phases by ∼60 meV, and higher electron mobility in the zincblende ZnO material

    Band offsets at ZnO/SiC heterojunction: Heterointerface in band alignment

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    Pulsed laser deposited ZnO layers on 6H-SiC substrates showed the six-fold symmetry, indicating a two-dimensional epitaxial growth mode. X-ray photoelectron spectroscopy was employed to study the valence band discontinuity and interface formation in the ZnO/6H-SiC heterojunction. The valence band offset was measured to be 1.38 ± 0.28 eV, leading to a conduction band offset value of 1.01 ± 0.28 eV. The resulting band lineup in epitaxial ZnO/6H-SiC heterojunction is determined to be of staggered-type alignment. Crow
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