Epitaxy, microstructure, and processing-structure relationships of TiO 2 thin films grown on sapphire (0001) by MOCVD
- PDF / 1,309,126 Bytes
- 10 Pages / 576 x 792 pts Page_size
- 14 Downloads / 242 Views
TiO 2 thin films have been deposited on sapphire (0001) substrates under various conditions by metal-organic chemical vapor deposition. The structural properties of the deposited films were characterized by x-ray diffraction and transmission electron microscopy. The important growth parameters were found to be the deposition temperature and the deposition rate. The ranges studied for the two parameters were 400 to 850 °C and 10 to 120 A/min, respectively. Depending on the growth conditions, most of the deposited films were either single-phase anatase or rutile, or a mixture of the two. These films were all epitaxial, but none of them were single-crystal films. Three distinct epitaxial relationships were observed between the films and the substrates, and, depending on the growth conditions, a deposited film can contain one, two, or all three of them. The fact that the films we obtained, although epitaxial, were never single crystal is explained based on the consideration of the difference in the rotational symmetries of the substrate surface and the film growth plane. We believe that it should be generally true that, in heteroepitaxial growth, a true single-crystal film can never be obtained as long as the point symmetry group of the substrate surface is not a subgroup of that of the film growth plane.
I. INTRODUCTION Over the past twenty years or so, deposition techniques for the growth of thin epitaxial films have been advanced to such a level that it is now possible to synthesize new classes of artificially structured materials exhibiting new or interesting physical properties.1'2 Quantum well structures,3"5 superlattice structures with periodicity of a few atomic layers,6 and metastable phases7'8 that do not exist in bulk form are a few examples. Studies of these materials are making rapid progress. Much of the research work to date has been driven by the motivation to produce materials for high performance electronic devices. Consequently, most of the effort in epitaxial materials has concentrated on semiconductors. Far less work has been done for nonsemiconductor materials. However, this situation has been changing rather rapidly in the past few years. More and more work has now been carried out to investigate materials systems such as insulators, metals, superconductors, or combinations of these materials with semiconductors. Particularly noticeable is the progress in oxide materials where a great variety of interesting physical properties can be exploited for various applications.9"11
"^Present address: Department of Physics, Pusan National University, Pusan, Korea.
2634 http://journals.cambridge.org
In an attempt to investigate the various fundamental aspects of oxide epitaxial film growth, we have recently carried out a series of work to study the processingstructure relationship of crystalline TiO2 and VO2 films grown on sapphire ( a - A l 2 O 3 ) single-crystal substrates by metal-organic chemical vapor deposition (MOCVD) in both single- and multilayered configurations.12"14 For these simple oxide sy
Data Loading...
