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Martin Heiss - One of the best experts on this subject based on the ideXlab platform.
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untangling the electronic band structure of Wurtzite gaas nanowires by resonant raman spectroscopy
ACS Nano, 2011Co-Authors: Bernt Ketterer, Jordi Arbiol, Emanuele Uccelli, Martin Heiss, Anna Fontcuberta I MorralAbstract:In semiconductor nanowires, the coexistence of Wurtzite and zinc-blende phases enables the engineering of the electronic structure within a single material. This presupposes an exact knowledge of the band structure in the Wurtzite phase. We demonstrate that resonant Raman scattering is a important tool to probe the electronic structure of novel materials. Exemplarily, we use this technique to elucidate the band structure of Wurtzite GaAs at the Γ point. Within the experimental uncertainty we find that the free excitons at the edge of the Wurtzite and the zinc-blende band gap exhibit equal energies. For the first time we show that the conduction band minimum in Wurtzite GaAs is of Γ7 symmetry, meaning a small effective mass. We further find evidence for a light-hole–heavy-hole splitting of 103 meV at 10 K.
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determination of the band gap and the split off band in Wurtzite gaas using raman and photoluminescence excitation spectroscopy
Physical Review B, 2011Co-Authors: Bernt Ketterer, Elisabeth Reiger, Martin Heiss, Andreas Rudolph, Marie J Livrozet, Anna Fontcuberta I MorralAbstract:GaAs nanowires with 100% Wurtzite structure are synthesized by the vapor-liquid-solid method in a molecular beam epitaxy system, using gold as a catalyst. We use resonant Raman spectroscopy and photoluminescence to determine the position of the crystal-field split-off band of hexagonal Wurtzite GaAs. The temperature dependence of this transition enables us to extract the value at 0 K, which is 1.982 eV. Our photoluminescence excitation spectroscopy measurements are consistent with a band gap of Wurtzite GaAs below 1.523 eV.
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direct correlation of crystal structure and optical properties in Wurtzite zinc blende gaas nanowire heterostructures
Physical Review B, 2011Co-Authors: Emanuele Uccelli, Martin Heiss, Sonia Conesaboj, Hsianghan Tseng, Adam Gali, Andreas Rudolph, F PeiroAbstract:A method for the direct correlation at the nanoscale of structural and optical properties of single GaAs nanowires is reported. Nanowires consisting of 100% Wurtzite and nanowires presenting zinc-blende/Wurtzite polytypism are investigated by photoluminescence spectroscopy and transmission electron microscopy. The photoluminescence of Wurtzite GaAs is consistent with a band gap of 1.5 eV. In the polytypic nanowires, it is shown that the regions that are predominantly composed of either zinc-blende or Wurtzite phase show photoluminescence emission close to the bulk GaAs band gap, while regions composed of a nonperiodic superlattice of Wurtzite and zinc-blende phases exhibit a redshift of the photoluminescence spectra as low as 1.455 eV. The dimensions of the quantum heterostructures are correlated with the light emission, allowing us to determine the band alignment between these two crystalline phases. Our first-principles electronic structure calculations within density functional theory, employing a hybrid-exchange functional, predict band offsets and effective masses in good agreement with experimental results.
Emanuele Uccelli - One of the best experts on this subject based on the ideXlab platform.
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untangling the electronic band structure of Wurtzite gaas nanowires by resonant raman spectroscopy
ACS Nano, 2011Co-Authors: Bernt Ketterer, Jordi Arbiol, Emanuele Uccelli, Martin Heiss, Anna Fontcuberta I MorralAbstract:In semiconductor nanowires, the coexistence of Wurtzite and zinc-blende phases enables the engineering of the electronic structure within a single material. This presupposes an exact knowledge of the band structure in the Wurtzite phase. We demonstrate that resonant Raman scattering is a important tool to probe the electronic structure of novel materials. Exemplarily, we use this technique to elucidate the band structure of Wurtzite GaAs at the Γ point. Within the experimental uncertainty we find that the free excitons at the edge of the Wurtzite and the zinc-blende band gap exhibit equal energies. For the first time we show that the conduction band minimum in Wurtzite GaAs is of Γ7 symmetry, meaning a small effective mass. We further find evidence for a light-hole–heavy-hole splitting of 103 meV at 10 K.
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direct correlation of crystal structure and optical properties in Wurtzite zinc blende gaas nanowire heterostructures
Physical Review B, 2011Co-Authors: Emanuele Uccelli, Martin Heiss, Sonia Conesaboj, Hsianghan Tseng, Adam Gali, Andreas Rudolph, F PeiroAbstract:A method for the direct correlation at the nanoscale of structural and optical properties of single GaAs nanowires is reported. Nanowires consisting of 100% Wurtzite and nanowires presenting zinc-blende/Wurtzite polytypism are investigated by photoluminescence spectroscopy and transmission electron microscopy. The photoluminescence of Wurtzite GaAs is consistent with a band gap of 1.5 eV. In the polytypic nanowires, it is shown that the regions that are predominantly composed of either zinc-blende or Wurtzite phase show photoluminescence emission close to the bulk GaAs band gap, while regions composed of a nonperiodic superlattice of Wurtzite and zinc-blende phases exhibit a redshift of the photoluminescence spectra as low as 1.455 eV. The dimensions of the quantum heterostructures are correlated with the light emission, allowing us to determine the band alignment between these two crystalline phases. Our first-principles electronic structure calculations within density functional theory, employing a hybrid-exchange functional, predict band offsets and effective masses in good agreement with experimental results.
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Raman spectroscopy of Wurtzite and zinc-blende GaAs nanowires: Polarization dependence, selection rules, and strain effects
Physical Review B, 2009Co-Authors: Ilaria Zardo, Sonia Conesa-boj, Francesca Peiró, Joan Ramon Morante, Jordi Arbiol, Emanuele Uccelli, Gerhard Abstreiter, A. Fontcuberta I MorralAbstract:Polarization-dependent Raman scattering experiments realized on single GaAs nanowires with different percentages of zinc-blende and Wurtzite structure are presented. The selection rules for the special case of nanowires are found and discussed. In the case of zinc-blende, the transversal optical mode E-1 (TO) at 267 cm(-1) exhibits the highest intensity when the incident and analyzed polarization are parallel to the nanowire axis. This is a consequence of the nanowire geometry and dielectric mismatch with the environment, and in quite good agreement with the Raman selection rules. We also find a consistent splitting of 1 cm(-1) of the E-1 (TO). The transversal optical mode related to the Wurtzite structure, E-2(H), is measured between 254 and 256 cm(-1), depending on the Wurtzite content. The azimuthal dependence of E-2(H) indicates that the mode is excited with the highest efficiency when the incident and analyzed polarization are perpendicular to the nanowire axis, in agreement with the selection rules. The presence of strain between Wurtzite and zinc-blende is analyzed by the relative shift of the E-1 (TO) and E-2(H) modes. Finally, the influence of the surface roughness in the intensity of the longitudinal optical mode on {110} facets is presented.
Sonia Conesaboj - One of the best experts on this subject based on the ideXlab platform.
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direct correlation of crystal structure and optical properties in Wurtzite zinc blende gaas nanowire heterostructures
Physical Review B, 2011Co-Authors: Emanuele Uccelli, Martin Heiss, Sonia Conesaboj, Hsianghan Tseng, Adam Gali, Andreas Rudolph, F PeiroAbstract:A method for the direct correlation at the nanoscale of structural and optical properties of single GaAs nanowires is reported. Nanowires consisting of 100% Wurtzite and nanowires presenting zinc-blende/Wurtzite polytypism are investigated by photoluminescence spectroscopy and transmission electron microscopy. The photoluminescence of Wurtzite GaAs is consistent with a band gap of 1.5 eV. In the polytypic nanowires, it is shown that the regions that are predominantly composed of either zinc-blende or Wurtzite phase show photoluminescence emission close to the bulk GaAs band gap, while regions composed of a nonperiodic superlattice of Wurtzite and zinc-blende phases exhibit a redshift of the photoluminescence spectra as low as 1.455 eV. The dimensions of the quantum heterostructures are correlated with the light emission, allowing us to determine the band alignment between these two crystalline phases. Our first-principles electronic structure calculations within density functional theory, employing a hybrid-exchange functional, predict band offsets and effective masses in good agreement with experimental results.
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structural and optical properties of high quality zinc blende Wurtzite gaas nanowire heterostructures
Physical Review B, 2009Co-Authors: D Spirkoska, Ilaria Zardo, Jordi Arbiol, Sonia Conesaboj, Anders Gustafsson, Frank Glas, Matthias Heigoldt, M H Gass, A Bleloch, S EstradeAbstract:The structural and optical properties of three different kinds of GaAs nanowires with 100% zinc-blende structure and with an average of 30% and 70% Wurtzite are presented. A variety of shorter and longer segments of zinc-blende or Wurtzite crystal phases are observed by transmission electron microscopy in the nanowires. Sharp photoluminescence lines are observed with emission energies tuned from 1.515 eV down to 1.43 eV when the percentage of Wurtzite is increased. The downward shift of the emission peaks can be understood by carrier confinement at the interfaces, in quantum wells and in random short period superlattices existent in these nanowires, assuming a staggered band offset between Wurtzite and zinc-blende GaAs. The latter is confirmed also by time-resolved measurements. The extremely local nature of these optical transitions is evidenced also by cathodoluminescence measurements. Raman spectroscopy on single wires shows different strain conditions, depending on the Wurtzite content which affects also the band alignments. Finally, the occurrence of the two crystallographic phases is discussed in thermodynamic terms.
Jinfeng Zhang - One of the best experts on this subject based on the ideXlab platform.
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new understanding on the different photocatalytic activity of Wurtzite and zinc blende cds
Applied Catalysis B-environmental, 2016Co-Authors: Jinfeng Zhang, S Wageh, Ahmeda AlghamdiAbstract:Abstract In general, Wurtzite CdS exhibits a higher photocatalytic activity than zinc-blende CdS. However, the underlying physicochemical reasons responsible for the differences of photocatalytic activity between the Wurtzite and zinc-blende CdS are still unclear. In this work, the structural characteristics, band structures, density of states, bond populations, optical properties and charge carrier effective mass of Wurtzite and zinc-blende CdS were investigated based on first-principle theoretical calculations. The calculated results indicate that the distortion of CdS4 tetrahedron units results in the formation of internal electric field in Wurtzite CdS, which is beneficial for the efficient separation and diffusion of photogenerated charge carriers. Contrarily, the internal electric field is absent in zinc-blende CdS. Moreover, the effective masses of photogenerated charge carriers of Wurtzite CdS are smaller than those of zinc-blende CdS, implying faster migration of photogenerated charge carriers to perform photocatalytic reactions on Wurtzite CdS surfaces. All the above factors result in the lower recombination rate of photogenerated charge carriers within Wurtzite CdS. Therefore, it is not surprising that Wurtzite CdS usually shows a higher photocatalytic activity than zinc-blende CdS. This investigation will provide some new understanding on the difference of photocatalytic activity between Wurtzite and zinc-blende CdS.
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effect of effective mass and spontaneous polarization on photocatalytic activity of Wurtzite and zinc blende zns
APL Materials, 2015Co-Authors: Ming Dong, Jinfeng ZhangAbstract:Semiconductor zinc sulphide (ZnS) has two common phases: hexagonal Wurtzite and cubic zinc-blende structures. The crystal structures, energy band structures, density of states (DOS), bond populations, and optical properties of Wurtzite and zinc-blende ZnS were investigated by the density functional theory of first-principles. The similar band gaps and DOS of Wurtzite and zinc-blende ZnS were found and implied the similarities in crystal structures. However, the distortion of ZnS4 tetrahedron in Wurtzite ZnS resulted in the production of spontaneous polarization and internal electric field, which was beneficial for the transfer and separation of photogenerated electrons and holes.
Jordi Arbiol - One of the best experts on this subject based on the ideXlab platform.
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untangling the electronic band structure of Wurtzite gaas nanowires by resonant raman spectroscopy
ACS Nano, 2011Co-Authors: Bernt Ketterer, Jordi Arbiol, Emanuele Uccelli, Martin Heiss, Anna Fontcuberta I MorralAbstract:In semiconductor nanowires, the coexistence of Wurtzite and zinc-blende phases enables the engineering of the electronic structure within a single material. This presupposes an exact knowledge of the band structure in the Wurtzite phase. We demonstrate that resonant Raman scattering is a important tool to probe the electronic structure of novel materials. Exemplarily, we use this technique to elucidate the band structure of Wurtzite GaAs at the Γ point. Within the experimental uncertainty we find that the free excitons at the edge of the Wurtzite and the zinc-blende band gap exhibit equal energies. For the first time we show that the conduction band minimum in Wurtzite GaAs is of Γ7 symmetry, meaning a small effective mass. We further find evidence for a light-hole–heavy-hole splitting of 103 meV at 10 K.
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Raman spectroscopy of Wurtzite and zinc-blende GaAs nanowires: Polarization dependence, selection rules, and strain effects
Physical Review B, 2009Co-Authors: Ilaria Zardo, Sonia Conesa-boj, Francesca Peiró, Joan Ramon Morante, Jordi Arbiol, Emanuele Uccelli, Gerhard Abstreiter, A. Fontcuberta I MorralAbstract:Polarization-dependent Raman scattering experiments realized on single GaAs nanowires with different percentages of zinc-blende and Wurtzite structure are presented. The selection rules for the special case of nanowires are found and discussed. In the case of zinc-blende, the transversal optical mode E-1 (TO) at 267 cm(-1) exhibits the highest intensity when the incident and analyzed polarization are parallel to the nanowire axis. This is a consequence of the nanowire geometry and dielectric mismatch with the environment, and in quite good agreement with the Raman selection rules. We also find a consistent splitting of 1 cm(-1) of the E-1 (TO). The transversal optical mode related to the Wurtzite structure, E-2(H), is measured between 254 and 256 cm(-1), depending on the Wurtzite content. The azimuthal dependence of E-2(H) indicates that the mode is excited with the highest efficiency when the incident and analyzed polarization are perpendicular to the nanowire axis, in agreement with the selection rules. The presence of strain between Wurtzite and zinc-blende is analyzed by the relative shift of the E-1 (TO) and E-2(H) modes. Finally, the influence of the surface roughness in the intensity of the longitudinal optical mode on {110} facets is presented.
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structural and optical properties of high quality zinc blende Wurtzite gaas nanowire heterostructures
Physical Review B, 2009Co-Authors: D Spirkoska, Ilaria Zardo, Jordi Arbiol, Sonia Conesaboj, Anders Gustafsson, Frank Glas, Matthias Heigoldt, M H Gass, A Bleloch, S EstradeAbstract:The structural and optical properties of three different kinds of GaAs nanowires with 100% zinc-blende structure and with an average of 30% and 70% Wurtzite are presented. A variety of shorter and longer segments of zinc-blende or Wurtzite crystal phases are observed by transmission electron microscopy in the nanowires. Sharp photoluminescence lines are observed with emission energies tuned from 1.515 eV down to 1.43 eV when the percentage of Wurtzite is increased. The downward shift of the emission peaks can be understood by carrier confinement at the interfaces, in quantum wells and in random short period superlattices existent in these nanowires, assuming a staggered band offset between Wurtzite and zinc-blende GaAs. The latter is confirmed also by time-resolved measurements. The extremely local nature of these optical transitions is evidenced also by cathodoluminescence measurements. Raman spectroscopy on single wires shows different strain conditions, depending on the Wurtzite content which affects also the band alignments. Finally, the occurrence of the two crystallographic phases is discussed in thermodynamic terms.
