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Proceedings ArticleDOI: 10.1109/ISDRS.2007.4422379

Evolution of annealed undoped single crystal ZnO Surfaces and Implications for Schottky Barrier height

01 Dec 2007-pp 1-1
Abstract: In this article, the authors investigate the origin of the surface roughness of thermally-treated ZnO surfaces via atomic force microscopy, X-ray photoelectron spectroscopy (XPS), and Schottky barrier measurements.

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Topics: Schottky barrier (65%), X-ray photoelectron spectroscopy (56%), Single crystal (53%) ...read more
References
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Open accessJournal ArticleDOI: 10.1103/PHYSREVLETT.86.3811
A. Wander1, Fred Schedin2, P. Steadman, A.G. Norris3  +5 moreInstitutions (4)
Abstract: The structures of the polar surfaces of ZnO are studied using ab initio calculations and surface x-ray diffraction. The experimental and theoretical relaxations are in good agreement. The polar surfaces are shown to be very stable; the cleavage energy for the (0001)-Zn and (0001;)-O surfaces is 4.0 J/m(2) comparable to 2.32 J/m(2) for the most stable nonpolar (1010) surface. The surfaces are stabilized by an electronic mechanism involving the transfer of 0.17 electrons between them. This leads to 2D metallic surface states, which has implications for the use of the material in gas sensing and catalytic applications.

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  • TABLE I. Reconstructions of the ZnO(0001) and 0001 surfaces. A negative value is a movement towards the bulk of the material. All values are given in Å, and the subscripts refer to bilayers numbered from the surface plane (e.g., Zn1 and O1 are the Zn and O ions in the surface bilayer).
    TABLE I. Reconstructions of the ZnO(0001) and 0001 surfaces. A negative value is a movement towards the bulk of the material. All values are given in Å, and the subscripts refer to bilayers numbered from the surface plane (e.g., Zn1 and O1 are the Zn and O ions in the surface bilayer).
  • FIG. 3. The band structure of the S7 slab. The energy scale is in hartrees (H). The partially occupied Zn-4s band and the unoccupied O-p band are labeled. Ef denotes the Fermi level of the system.
    FIG. 3. The band structure of the S7 slab. The energy scale is in hartrees (H). The partially occupied Zn-4s band and the unoccupied O-p band are labeled. Ef denotes the Fermi level of the system.
  • FIG. 2. Experimental CTR datapoints displayed on a log10 scale. The fitted CTR profiles are shown as solid curves through the datapoints, shown offset along the y axis for clarity.
    FIG. 2. Experimental CTR datapoints displayed on a log10 scale. The fitted CTR profiles are shown as solid curves through the datapoints, shown offset along the y axis for clarity.
  • FIG. 1. A side view of the polar (0001) and 0001 ZnO surfaces.
    FIG. 1. A side view of the polar (0001) and 0001 ZnO surfaces.

376 Citations


Journal ArticleDOI: 10.1063/1.1536264
Abstract: Reverse bias current–voltage measurements of ∼100-μm-diameter gold Schottky contacts deposited on as-received, n-type ZnO(0001) wafers and those exposed for 30 min to a remote 20% O2/80% He plasma at 525±20 °C and cooled either in vacuum from 425 °C or the unignited plasma gas have been determined. Plasma cleaning resulted in highly ordered, stoichiometric, and smooth surfaces. Contacts on as-received material showed μA leakage currents and ideality factors >2. Contacts on plasma-cleaned wafers cooled in vacuum showed ∼36±1 nA leakage current to −4 V, a barrier height of 0.67±0.05 eV, and an ideality factor of 1.86±0.05. Cooling in the unignited plasma gas coupled with a 30 s exposure to the plasma at room temperature resulted in decreases in these parameters to ∼20 pA to −7 V, 0.60±0.05 eV, and 1.03±0.05, respectively. Differences in the measured and theoretical barrier heights indicate interface states. (0001) and (0001) are used in this letter to designate the polar zinc- and oxygen-terminated surfac...

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Topics: Plasma cleaning (55%), Schottky diode (50%)

365 Citations


Journal ArticleDOI: 10.1103/PHYSREVB.68.245409
Georg Kresse1, Olga Dulub2, Ulrike Diebold2Institutions (2)
11 Dec 2003-Physical Review B
Abstract: Density-functional calculations for the (0001)-Zn surface of wurtzite ZnO are reported. Different stabilization mechanisms, such as metallization of the surface layer, adsorption of OH groups or O adatoms, the formation of Zn vacancies, and large scale triangular reconstructions are considered. The calculations indicate that isolated Zn vacancies or O adatoms are unfavorable compared to triangular reconstructions. In the absence of hydrogen, these triangular features are stable under any realistic temperature and pressure. When hydrogen is present, the reconstruction is lifted, and hydroxyl groups stabilize the ideal otherwise unreconstructed surface. The transition between the unreconstructed hydroxyl covered surface and the triangular shaped features occurs abruptly; OH groups lift the reconstruction, but their adsorption is energetically unfavorable on the triangularly reconstructed surface.

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Topics: Surface layer (51%)

319 Citations


Journal ArticleDOI: 10.1103/PHYSREVB.66.081402
M. Kunat1, St. Gil Girol1, Th. Becker1, Uwe Burghaus1  +1 moreInstitutions (1)
20 Aug 2002-Physical Review B
Abstract: A reinvestigation of the O-terminated, polar surface of zinc oxide, O-ZnO(0001\ifmmode\bar\else\textasciimacron\fi{}), using scattering of thermal energy He atoms reveals the presence of a (1\ifmmode\times\else\texttimes\fi{}3) reconstruction for the clean surface. This finding is at variance with the results of previous works, where the same surface was found to be unreconstructed. Results for the hydrogen saturated H(1\ifmmode\times\else\texttimes\fi{}1) O-ZnO(0001\ifmmode\bar\else\textasciimacron\fi{}) surface, which has also been investigated, suggest that the presence of H atoms has a strong impact on the structure of the O-terminated ZnO surfaces.

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170 Citations


Journal ArticleDOI: 10.1103/PHYSREVLETT.90.106102
Volker Staemmler1, Karin Fink1, Bernd Meyer1, Dominik Marx1  +4 moreInstitutions (1)
Abstract: The determination of the structure of inhomogeneous metal-oxide surfaces represents a formidable task. With the present study, we demonstrate that using the binding energy of a probe molecule, CO, is a reliable tool to validate structural models for such complex surfaces. Combining several types of first-principles calculations with advanced molecular beam methods, we are able to provide conclusive evidence that the polar O-terminated surface of ZnO is either reconstructed or hydrogen covered. This finding has important consequences for the ongoing discussion regarding the stabilization mechanism of the electrostatically unstable ("Tasker type 3") polar ZnO surfaces.

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160 Citations