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26 Apr 2010

Volume 96, Issue 17, Articles (17xxxx)

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Appl. Phys. Lett. 96, 173501 (2010); http://dx.doi.org/10.1063/1.3409475 (3 pages)

Seoung-Ki Lee, Houk Jang, Musarrat Hasan, Jae Bon Koo, and Jong-Hyun Ahn
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Nitrogen vacancies at InN (1math00) surfaces: A theoretical study

A. Terentjevs, A. Catellani, and G. Cicero

Appl. Phys. Lett. 96, 171901 (2010); http://dx.doi.org/10.1063/1.3409224 (3 pages) | Cited 7 times

Online Publication Date: 28 April 2010

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We present an ab initio atomistic study of the effects of nitrogen vacancies both in InN bulk and at (1math00) nonpolar surface and confirm that these defects act as n-type impurities. Based on the dependence of the vacancy formation energy on the distance from the surface, we predict that at thermodynamic equilibrium these defects tend to segregate in the outermost surface layers reaching a concentration which is few orders of magnitude higher than in the bulk phase. Considering out-of-equilibrium growth and in view of the large calculated energy barrier that characterize vacancy diffusion, we also predict that the N enriched layer will extend hundreds of angstroms from the surface for typical growth processes. This vacancy accumulation at surface is consistent with the observed high electron accumulation layer.
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73.20.Hb Impurity and defect levels; energy states of adsorbed species
68.35.Dv Composition, segregation; defects and impurities
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
61.72.jd Vacancies

Optical and electronic properties of post-annealed ZnO:Al thin films

Yumin Kim, Woojin Lee, Dae-Ryong Jung, Jongmin Kim, Seunghoon Nam, Hoechang Kim, and Byungwoo Park

Appl. Phys. Lett. 96, 171902 (2010); http://dx.doi.org/10.1063/1.3419859 (3 pages) | Cited 25 times

Online Publication Date: 30 April 2010

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This study examined the optical and electronic properties of post-annealed Al-doped ZnO (ZnO:Al) thin films. The lowest resistivity was observed after annealing a sputter-deposited ZnO:Al film at 350 °C. X-ray photoelectron spectroscopy revealed a ∼ 0.4 eV shift in the Fermi level when the carrier concentration was increased to 1.6×1020 cm−3 by Al doping and annealing. The optical band gap increased from 3.2 eV for insulating ZnO to 3.4 eV for conducting ZnO:Al, and was associated with conduction-band filling up to ∼ 0.4 eV in a renormalized band gap. Schematic band diagrams are shown for the ZnO and ZnO:Al films.
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78.66.Hf II-VI semiconductors
81.15.Cd Deposition by sputtering
79.60.Bm Clean metal, semiconductor, and insulator surfaces
61.72.Cc Kinetics of defect formation and annealing
73.61.Ga II-VI semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.20.Nr Semiconductor compounds

Structural transformation induced changes in the optical properties of nanocrystalline tungsten oxide thin films

S. K. Gullapalli, R. S. Vemuri, and C. V. Ramana

Appl. Phys. Lett. 96, 171903 (2010); http://dx.doi.org/10.1063/1.3421540 (3 pages) | Cited 21 times

Online Publication Date: 30 April 2010

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Nanocrystalline tungsten oxide (WO3) films were grown by reactive magnetron sputter-deposition. The structure and optical properties of WO3 films were evaluated using grazing incidence x-ray diffraction and optical spectroscopic measurements. The effect of ultramicrostructure was significant on the optical characteristics of WO3 films. The band gap decreases from 3.25 to 2.92 eV with increasing grain-size from ∼ 9 to 50 nm while the films exhibit a transition from monoclinic to tetragonal phase. A direct microstructure-property relationship found suggests that tuning properties of WO3 films for desired applications can be achieved by tuning the conditions and controlling the phase.
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68.55.A- Nucleation and growth
81.07.Bc Nanocrystalline materials
61.46.-w Structure of nanoscale materials
81.15.Cd Deposition by sputtering
78.66.Li Other semiconductors
78.20.-e Optical properties of bulk materials and thin films
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