Annealing effect on properties of ZnO thin films grown on LiNbO3 substrates by MOCVD

ZnO films were grown on (0 0 0 1) LiNbO3 substrates by metal organic chemical vapor deposition (MOCVD). Annealing of ZnO films was performed in air for I h at 800 degrees C. The effects of annealing on the structural and optical properties of ZnO thin films on LiNbO3 substrates were investigated using X-ray diffraction (XRD), atomic force microscopy (AFM) and photoluminescence (PL) measurements. XRD patterns and AFM showed that the as-grown and the annealed ZnO films grown on LiNbO3 substrates had c-axis preferential orientation, the crystallinity of the ZnO films grown on LiNbO3 Substrates was improved, and the grain size increased by annealing. The PL spectra showed that the intensity of the UV near-band-edge peak was increased after annealing, while the intensity of visible peak (deep-level emission) decreased. (c) 2005 Elsevier B.V. All rights reserved.

Growth and properties of ZnO thin film on beta-Ga2O3(100) substrate by pulsed laser deposition

Zinc oxide (ZnO) thin films were grown on the beta-Ga2O3 (100) substrate by pulsed laser deposition (PLD). X-ray diffraction (XRD) indicated that the ZnO films are c-axis oriented. The optical and electrical properties of the films were investigated. The room temperature Photoluminescence (PL) spectrum showed a near band emission at 3.28 eV with two deep level emissions. Optical absorption indicated a visible exciton absorption at room temperature. The as-grown films had good electrical properties with the resistivities as low as 0.02 Omega cm at room temperature. Thus, beta-Ga2O3 (100) substrate is shown to be a suitable substrate for fabricating ZnO film. (c) 2006 Elsevier B.V. All rights reserved.

Optical properties of ZnO thin film on gamma-LiAlO2 substrate grown by pulsed laser deposition

Optical properties were investigated of ZnO thin films grown oil (100) gamma-LiAlO2 (LAO) substrates by pulsed laser deposition method. C-axis oriented ZnO film was grown oil (100) LAO substrate at the substrate temperature of 550 degrees C. The transmittances of the films were over 85%. Peaks attributed to excitons were seen in the absorption spectra, indicating that the thin films have high crystallinity. Photoluminescence spectra were observed at room temperature; the peak at 550 urn is ascribed to oxygen vacancies in the ZnO films caused by the diffusion of Li from the substrate into the film during deposition. (c) 2005 Elsevier B.V. All rights reserved.

Structural, morphological and optical properties of ZnO thin films grown on gamma-LiAlO2 substrate by pulsed laser deposition

ZnO thin films were deposited on the substrates of (100) gamma-LiAlO2 at 400, 550 and 700 degrees C using pulsed laser deposition (PLD) with the fixed oxygen pressure of 20 Pa, respectively. When the substrate temperature is 400 degrees C, the grain size of the film is less than 1 mu m observed by Leitz microscope and measured by X-ray diffraction (XRD). As the substrate temperature increases to 550 degrees C, highly-preferred c-orientation and high-quality ZnO film can be attained. While the substrate temperature rises to 700 degrees C, more defects appears on the surface of film and the ZnO films become polycrystalline again possibly because more Li of the substrate diffused into the ZnO film at high substrate temperature. The photoluminescence (PL) spectra of ZnO films at room temperature show the blue emission peaks centered at 430 nm. We suggest that the blue emission corresponds to the electron transition from the level of interstitial Zn to the valence band. Meanwhile, the films grown on gamma-LiAlO2 (LAO) exhibit green emission centered at 540 nm, which seemed to be ascribed to excess zinc and/or oxygen vacancy in the ZnO films caused by diffusion of Li. from the substrates into the films during the deposition.

Annealing effects of sapphire substrate on properties of ZnO films grown by magnetron sputtering

The annealing effects of sapphire substrates on the quality of epitaxial ZnO films grown by dc reactive magnetron sputtering were studied. The atomic steps formed on (0001) sapphire (alpha-Al2O3) substrates surface by annealing at high temperature were analyzed by atomic force microscopy. Their influence on the growth of ZnO films was examined by X-ray diffraction and photoluminescence measurements. Experimental results indicate that the film quality is strongly affected by annealing treatment of the sapphire substrate surface. The optimum annealing temperature of sapphire substrates for ZnO grown by magnetron sputtering is 1400 degrees C for 1 h in air.

Spectroscopic properties of Ce : YAP scintillation crystal grown by temperature gradient technique

Spectroscopic properties of Ce-doped yttrium orthoaluminate (Ce:YAlO3 or Ce:YAP) crystals grown by temperature gradient technique (TGT) were investigated, and the effects of the growth conditions on the properties were analyzed.. Methods of optical absorption (OA), photoluminescence (PL), photoluminescence decay (PLD), X-ray excited luminescence (XL) and cathodeluminescence (CL) were used in these investigations. The results showed that the absorption band peak at 202, 394 and 532 nm originated from F and F+ color center induced by the weak reducing growth atmosphere, green emission band near 500 ran derived from Ce3+ -Ce3+ pairs and band at 650 similar to 850 run from some unintentional impurity in crystals.

Enhancement of ferromagnetic properties in In1.99Co0.01O3 by additional Cu doping

This paper reports room-temperature ferromagnetism in Co- and Cu-doped In2O3 samples synthesized by a solid-state reaction method. Structure and composition analyses revealed that Co and Cu were incorporated into the In2O3 lattices. Photoluminescence measurement revealed an additional emission at 520 urn from these doped samples. The magnetic measurement showed that additional Cu doping greatly enhanced the ferromagnetism of In1.99Co0.01O3 bulk samples. The implication of the effects of additional Cu doping is also discussed. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Anisotropic crystallographic properties, strain, and their effects on band structure of m -plane GaN on LiAlO2 (100)

The m-plane GaN films grown on LiAlO2(100) by metal-organic chemical vapor deposition exhibit anisotropic crystallographic properties. The Williamson-Hall plots point out they are due to the different tilts and lateral correlation lengths of mosaic blocks parallel and perpendicular to GaN[0001] in the growth plane. The symmetric and asymmetric reciprocal space maps reveal the strain of m-plane GaN to be biaxial in-plane compress epsilon(xx)=-0.79% and epsilon(zz)=-0.14% with an out-of-plane dilatation epsilon(yy)=0.38%. This anisotropic strain further separates the energy levels of top valence band at Gamma point. The energy splitting as 37 meV as well as in-plane polarization anisotropy for transitions are found by the polarized photoluminescence spectra at room temperature. (c) 2008 American Institute of Physics.

Enhancement of near-band edge photoluminescence of ZnO thin films by employing MgF2 buffer layer

ZnO/MgF2/ZnO sandwich structure films were fabricated. The effects of a buffer layer on structure and optical properties of ZnO films were investigated by X-ray diffraction, photoluminescence, optical transmittance and absorption measurements. Measurement results showed that the buffer layer had the effects of improving the quality of ZnO films and releasing the residual stresses in the films. The near-band edge emissions of ZnO films deposited on the MgF2 buffer layer were significantly enhanced compared with those deposited on bare substrate due to the smaller lattice mismatch between MgF2 and ZnO than that between fused silica and ZnO. (c) 2006 Elsevier B.V. All rights reserved.

Enhancement of near-band-edge photoluminescence of ZnO thin films in sandwich configuration at room temperature

ZnO/ITO/ZnO sandwich structure films were fabricated. The effects of buffer layer on the structure and optical properties of ZnO films were investigated by x-ray diffraction (XRD), photoluminescence, optical transmittance, and absorption measurements. XRD spectra indicate that a buffer layer has the effects of lowering the grain orientation of ZnO films and increasing the residual stresses in the films. The near-band-edge emissions of ZnO films deposited on both single indium tin oxide (ITO) buffer and ITO/ZnO double buffers are significantly enhanced compared with that deposited on a bare substrate due to the quantum confinement effect. (C) 2006 American Institute of Physics.

Influence of buffer layer thickness on the structure and optical properties of ZnO thin films

A series of ZnO thin films were deposited on ZnO buffer layers by DC reactive magnetron sputtering. The buffer layer thickness determination of microstructure and optical properties of ZnO films was investigated by X-ray diffraction (XRD), photoluminescence (PL), optical transmittance and absorption measurements. XRD results revealed that the stress of ZnO thin films varied with the buffer layer thickness. With the increase of buffer layer thickness, the band gap edge shifted toward longer wavelength. The near-band-edge (NBE) emission intensity of ZnO films deposited on ZnO buffer layer also varied with the increase of thickness due to the spatial confinement increasing the Coulomb interaction between electrons and holes. The PL measurement showed that the optimum thickness of the ZnO buffer layer was around 12 nm. (c) 2005 Elsevier B.V. All rights reserved.

Influence of different post-treatments on the structure and optical properties of zinc oxide thin films

Zinc oxide (ZnO) films with c-oriented were grown on fused quartz glass substrates at room temperature using dc reactive magnetron sputtering. The as-grown films were annealed at 700 degrees C in air and bombarded by ion beam, respectively. The effects of post-treatments on the structural and optical properties of the ZnO films were investigated by X-ray diffraction (XRD), photoluminescence (PL), optical transmittance and absorption measurements. The XRD spectra indicate that the crystal quality of ZnO films has been improved by both the post-treatments. Compared with the as-grown sample, both annealed and bombarded samples exhibited blueshift in the UV emission peaks, and a strong green emission was found in the annealed ZnO film. In both optical transmittance and absorption spectra, a blueshift of the band-gap edge was observed in the bombarded film, while a redshift was observed in the annealed film. (c) 2004 Elsevier B.V. All rights reserved.

Influence of oxygen partial pressure on the structure and photoluminescence of direct current reactive magnetron sputtering ZnO thin films

The effects of oxygen partial pressure on the structure and photoluminescence (PL) of ZnO films were studied. The films were prepared by direct current (DC) reactive magnetron sputtering with various oxygen concentrations at room temperature. With increasing oxygen ratio, the structure of films changes from zinc and zinc oxide phases, single-phase ZnO, to the (002) orientation, and the mechanical stresses exhibit from tensile stress to compressive stress. Films deposited at higher oxygen pressure show weaker emission intensities, which may result from the decrease of the oxygen vacancies and zinc interstitials in the film. This indicates that the emission in ZnO film originates from the oxygen vacancy and zinc interstitial-related defects. From optical transmittance spectra of ZnO films, the plasma edge shifts towards the shorter wavelength with the improvement of film stoichiometry. (C) 2004 Elsevier B.V. All rights reserved.

Influences of CO2 laser irradiation on the structure and photoluminescence of zinc oxide thin films

CO2 laser irradiation experiments on ZnO thin films are reported. The structural, optical, luminescent and vibrational properties of the samples were investigated by X-ray diffraction (XRD), transmittance, photoluminescence (PL) and Raman measurements. XRD results show that the crystalline of the irradiated films was improved. The (002) peaks of irradiated ZnO films shift to. higher 20 angles due to the stress relaxation in the case of laser beam irradiation. From optical transmittance spectra, all films exhibit high transmittance in the visible range, the optical band edge of irradiated films showed a redshift compared with that of as-grown films. Compared with the as-grown films, the photoluminescence emission (in particular the relative intensities of visible emissions) intensities of irradiated samples enhanced. In the Raman scattering spectral both the A I. and E modes exhibited slight Raman blueshift. (c) 2005 Elsevier B.V. All rights reserved.

Non-linear photoluminescence from graphene

Graphene is in the focus of research due to its unique electronic and optical properties. Intrinsic graphene is a zero gap semiconductor with a linear dispersion relation for E-k leading to zero-effective-mass electrons and holes described by Fermi-Dirac theory. Since pristine graphene has no bandgap no photoluminescence would be expected. However, recently several groups showed non-linear photoluminescence from pristine graphene putting forward different physical models explaining this remarkable effect [1-3]. © 2011 IEEE.