Effect of oxygen partial pressure during pulsed laser deposition on the orientation of CeO 2 thin films grown on (100) s
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The effect of oxygen partial pressure on the preferred orientation of CeO2 thin films was investigated by depositing CeO2 thin films and Pb(Zr,Ti)O3/CeO2 multilayers on Si (100) substrates by pulsed laser deposition. CeO2 thin films exhibited random polycrystalline grain structures at high oxygen partial pressure (艌40 mtorr), a result that is contrary to previous reports. The relationship of the preferred orientations observed between Pb(Zr,Ti)O3 films and the CeO2 layer underneath confirmed that random polycrystalline CeO2 was obtained at high oxygen partial pressure. It was suggested that x-ray diffraction data in previous reports might have been misinterpreted.
There has been much interest in CeO2 thin films as gate dielectrics in silicon metal-oxide-semiconductor field-effect transistors and as buffer layers for superconducting or ferroelectric thin films on silicon. CeO2 is chemically inert, has a CaF2 structure with its lattice constant (0.541 nm) well matched with that of Si (0.543 nm), and has a dielectric constant (⑀ ∼ 26) that is higher than that of SiO2 (⑀ ∼ 3.7). Although (111)-oriented epitaxial CeO2 thin films can be directly grown on Si (111) substrates,1,2 the preferred orientations of CeO2 thin films directly deposited on Si (100) substrates have been known to be affected by the ambient oxygen pressure and the existence of the native SiO2 layer.3,4 CeO2 films have been found to be (110)-oriented on native-oxide-free Si (100) substrates at very low oxygen partial pressure (10 mtorr) report direct growth of (100)-oriented CeO2 thin films on Si (100) substrates by pulsed laser deposition (PLD).7–10
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Present address: School of Materials Engineering and School of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907 J. Mater. Res., Vol. 18, No. 8, Aug 2003
http://journals.cambridge.org
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These latter claims were based on the observation of 2007–9 or 4007,10 reflection of CeO2 in x-ray diffraction (XRD) patterns. However, careful review of the published data raises two concerns in the interpretation of the XRD data. First, although the 200 reflection of Si is forbidden by extinction rules, it can appear by double diffraction or as a result of symmetry breaking due to strain. Because of the close lattice spacing, the 200 reflection of Si is very difficult to distinguish from that of CeO2. Second, the small difference in lattice spacing between (400) planes of Si and CeO2 makes it very difficult to conclusively identify the reflection, especially when the 400 reflection of Si is split due to the difference in wavelength between K␣1 (0.1540562 nm for Cu) and K␣2 (0.1544390 nm for Cu) radiation. The purpose of this study is to investigate the orientation of the CeO2 film deposited at high oxygen partial pressure with the objective of resolving the apparent discrepancy in reports at high and low oxygen partial pressure. An indirect but simple method for confirming the orientation of a thin CeO2 film is to investigate the orientation of a thicker pe
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