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A transparent and conducting ZnO:Er:Yb thin film with upconversion properties has been achieved after being annealed with continuous laser radiation just before the ablation point of the material. This work demonstrates that the laser energy preserves the conductivity of the film and at the same time creates an adequate surrounding for Er and Yb to produce visible upconversion at 660, 560, 520, and 480 nm under 980 nm laser excitation. The relation between the structural, electrical and upconversion properties is discussed. It is observed that the laser energy melts part of the material, which recrystallizes creating rare earth oxides and two different wurtzite structures, one with substitutional rare earths and oxygen vacancies (responsible for the conductivity) and the other without substitutional rare earth ions (responsible for the upconversion emission).

Development of cost-effective, highly reproducible non-conventional fabrication techniques for anisotropic metal nanostructures is essential to realizing potential applications of plasmonic devices, photonic devices, and surface enhanced Raman scattering (SERS) phenomenon based sensors. This report highlights the fabrication of nanotriangle arrays via nanoimprinting to overcome difficulties in creating large-area SERS active substrates with uniform, reproducible Raman signals. Electron beam lithography of anisotropic nanostructures, formation of arrays of nanotriangles in silicon and the transfer of triangular shapes to polymethylmethacrylate (PMMA) sheets via nanoimprinting have not been reported elsewhere. The reuse of silicon masters offers potential for production of low cost SERS substrates. The SERS activity and reproducibility of nanotriangles are illustrated and a consistent average enhancement factor of up to ~2.9 × 1011, which is the highest value reported for a patterned SERS substrate, is achieved., Peer Reviewed, Postprint (author's final draft)

In this work, zinc indium tin oxide layers with different compositions are used as the active layer of thin film transistors. This multicomponent transparent conductive oxide is gaining great interest due to its reduced content of the scarce indium element. Experimental data indicate that the incorporation of zinc promotes the creation of oxygen vacancies. In thin-film transistors this effect leads to a higher threshold voltage values. The field-effect mobility is also strongly degraded, probably due to coulomb scattering by ionized defects. A post deposition annealing in air reduces the density of oxygen vacancies and improves the fieldeffect mobility by orders of magnitude. Finally, the electrical characteristics of the fabricated thin-film transistors have been analyzed to estimate the density of states in the gap of the active layers. These measurements reveal a clear peak located at 0.3 eV from the conduction band edge that could be attributed to oxygen vacancies.

Back surface passivation is a well-known method to reduce carrier recombination and hence improves the efficiency of crystalline silicon solar cells. In this manuscript, we critically analyze the role of this process for a-Si/c-Si heterojunction solar cells through a combination of device fabrication, multiple characterization techniques, and modeling. Curiously, our experimental results indicate that dark current characteristics of these devices do not scale in accordance with the improvements in carrier lifetime achieved through back surface passivation. Our results indicate these puzzling experimental results could be due to the possibility that carrier injection from crystalline silicon base significantly contributes to the dark current of these devices. This result has obvious and significant implications towards understanding the device physics and efficiency optimization of a-Si/c-Si heterojunction devices., Peer Reviewed, Postprint (published version)

In this work, zinc indium tin oxide layers with different compositions are used as the active layer of thin film transistors. This multicomponent transparent conductive oxide is gaining great interest due to its reduced content of the scarce indium element. Experimental data indicate that the incorporation of zinc promotes the creation of oxygen vacancies, which results in a higher free carrier density. In thin-film transistors this effect leads to a higher off current and threshold voltage values. The field-effect mobility is also strongly degraded, probably due to coulomb scattering by ionized defects. A post deposition annealing in air reduces the density of oxygen vacancies and improves the field-effect mobility by orders of magnitude. Finally, the electrical characteristics of the fabricated thin-film transistors have been analyzed to estimate the density of states in the gap of the active layers. These measurements reveal a clear peak located at 0.3 eV from the conduction band edge that could be attributed to oxygen vacancies. (C) 2013 Elsevier B.V. All rights reserved., Postprint (published version)

Vertically aligned ZnO nanorod array (ZNA) was deposited by electrodeposition technique over glass substrate coated with Al doped ZnO (AZO). The photo-luminescence spectrum of the ZNA showed a near band edge emission and deep level emission (DLE). The resolved DLE spectrum indicates the formation of various defect levels within the band gap of ZnO. P-type CuO was deposited on ZNA to form ZNA/CuO heterojunction. The voltage-current (V-I) characteristics show a turn on voltage of 0.65V. The device showed good rectification behavior and a rectification ratio of 50 at 1V. The heterojunction with a device structure AZO/ZNA/CuO/Au showed good response on ultra violet (UV) illumination. The device has stability even after long exposures to atmospheric conditions and UV light., Peer Reviewed, Postprint (published version)

Indium tin oxide (ITO) is one of the widely used transparent conductive oxides (TCO) for application as transparent electrode in thin film silicon solar cells or thin film transistors owing to its low resistivity and high transparency. Nevertheless, indium is a scarce and expensive element and ITO films require high deposition temperature to achieve good electrical and optical properties. On the other hand, although not competing as ITO, doped Zinc Oxide (ZnO) is a promising and cheaper alternative. Therefore, our strategy has been to deposit ITO and ZnO multicomponent thin films at room temperature by radiofrequency (RF) magnetron co-sputtering in order to achieve TCOs with reduced indium content. Thin films of the quaternary system Zn-In-Sn-O (ZITO) with improved electrical and optical properties have been achieved. The samples were deposited by applying different RF powers to ZnO target while keeping a constant RF power to ITO target. This led to ZITO films with zinc content ratio varying between 0 and 67%. The optical, electrical and morphological properties have been thoroughly studied. The film composition was analysed by X-ray Photoelectron Spectroscopy. The films with 17% zinc content ratio showed the lowest resistivity (6.6 × 10 - 4 Ω cm) and the highest transmittance (above 80% in the visible range). Though X-ray Diffraction studies showed amorphous nature for the films, using High Resolution Transmission Electron Microscopy we found that the microstructure of the films consisted of nanometric crystals embedded in a compact amorphous matrix. The effect of post deposition annealing on the films in both reducing and oxidizing atmospheres were studied. The changes were found to strongly depend on the zinc content ratio in the films.

Bi1.5Zn1Nb1.5O7 (BZN) epitaxial thin films were grown by pulsed laser deposition on Al2O3 with a double ZnO buffer layer through domain matching epitaxy (DME) mechanism. The pole figure analysis and reciprocal space mapping revealed the single crystalline nature of the thin film. The pole figure analysis also shows a 60º twinning for the (222) oriented crystals. Sharp intense spots in the SAED pattern also indicate the high crystalline nature of BZN thin film. The Fourier filtered HRTEM images of the BZN-ZnO interface confirms the domain matched epitaxy of BZN with ZnO buffer. An electric field dependent dielectric tunability of 68% was obtained for the BZN thin films with inter digital capacitors patterned over the film.

We report on a growth study of MgO films deposited on Al2O3(0001) substrates by magnetron sputtering. The films exhibited a preferred rocksalt MgO(111) orientation. Surprisingly, depending on the O2 gas flow ratio, a structure of graphiticlike wurtzite MgO(0001) has been revealed. The observed Mg-O perpendicular bond length reduction is accompanied by an atomically flat surface morphology for the development of MgO(111) films; the transition to the bulk rocksalt structure occurs in the 3-6 nm coverage range. Previously, relaxation of the electrostatic instability of MgO(111) films accompanied by an in-plane lattice increase has been suggested theoretically [Phys. Rev. Lett. 98, 205701 (2007)]. Here, relying on ab initio calculations, we infer that Mg vacancies facilitate the lattice match with the substrate. This mechanism suggests methods to engineer oxide heterostructures.