Planar defects in ZnO thin films deposited on optical fibers and flat substrates
- PDF / 505,641 Bytes
- 10 Pages / 612 x 792 pts (letter) Page_size
- 5 Downloads / 234 Views
MATERIALS RESEARCH
Welcome
Comments
Help
Planar defects in ZnO thin films deposited on optical fibers and flat substrates Laurent Sagalowicza) and Glen R. Foxb) Laboratoire de C´eramique, D´epartement des Mat´eriaux, EPFL, 1015 Lausanne, Switzerland (Received 10 July 1998; accepted 10 November 1998)
The microstructure and the defects of ZnO coatings deposited at room temperature by sputtering onto fibers and flat substrates were characterized using transmission electron microscopy (TEM), scanning electron microscopy, and x-ray diffraction (XRD). XRD shows that the films have a [0001] preferred orientation and a large angular width of the 0002 reflection. According to TEM observations, the film microstructure consists of columnar grains which contain large concentrations of basal planar defects and dislocations. High-resolution transmission electron microscopy analysis and the associated image simulation are in full agreement with the presence of single (type I) and double (type II) stacking faults. The relation between the observed defects and the 0002 peak broadening is discussed.
I. INTRODUCTION
ZnO thin films have been studied for a wide variety of applications including piezoelectric surface acoustic wave devices,1,2 varistors,3–5 optical waveguides,6 transparent electrodes,7 and gas sensors.8 In addition, ZnO coatings deposited on optical fibers show promise for the development of new active all-fiber devices including phase modulators,9,10 wavelength modulators,11 electric field sensors,12,13 and flexural actuators.14 It is well established that the microstructure, in particular the [0001] preferred orientation, of ZnO thin films strongly influences both electrical and optical properties. In fact, ZnO thin films cannot be used for certain applications, e.g., piezoelectric sensors and actuators, unless they exhibit a preferred orientation, which is commonly [0001] perpendicular to the substrate plane for films deposited by sputtering.6,15 In this article, the microstructures of [0001] textured ZnO thin films deposited onto flat and fiber substrates are analyzed from the atomic to the micron scale in order to give more insight into which microstructural features are present that can influence thin film properties. ZnO thin films deposited by sputter deposition methods tend to exhibit columnar microstructures for a relatively broad range of deposition conditions. The occurrence of these columnar microstructures has been confirmed by several studies that have employed scanning electron microscopy (SEM).16–19 X-ray diffraction (XRD) has been used to determine that the columnar grains tend to exhibit a preferred orientation with the [0001] direction perpendicular to the
a)
e-mail: [email protected] Present address: Ramtron International Corporation, 1850 Ramtron Drive, Colorado Springs, Colorado 80921.
b)
1876
http://journals.cambridge.org
J. Mater. Res., Vol. 14, No. 5, May 1999
Downloaded: 19 Mar 2015
plane of a planar substrate. The standard deviation of the x-ray diffraction rocking curv
Data Loading...
