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XPS investigations of NdGaO3 wafers

Ewa Talik 1Magdalena M. Kruczek 1Halina Sakowska 2

1. University of Silesia, Katowice, Poland
2. Institute of Electronic Materials Technology (ITME), Wólczyńska 133, Warszawa 01-919, Poland


X-ray photoelectron spectroscopy was used to examine the electronic structure of neodymium gallium perovskite single crystals. They are a pseudo - cubic materials being used as a substrate for epitaxial growth of high temperature superconductors and for group III nitrides (such as GaN). The NdGaO3 single crystals were grown by the Czochralski method. In order to prepare specimens for XPS analysis, crystals were cut into wafers (0.7 mm thickness), lapped and polished (0.1 m SiO2). Before the XPS analysis substrates were chemically etched in H3PO4 at 650C for 10 min.
The electronic structure measurements of the unpolished, polished and etched (011) wafer planes were performed. For a comparison one wafer was broken perpendicular to the (011) plane, to obtain a fresh surface, without contamination with adsorbed carbon and oxygen. The XPS spectra in the wide energy range 0 - 1400 eV show a presence, for all measured crystals, a contamination with carbon. In the treated crystals a calcium contamination was found. The eatched crystal surface was additionally contaminated with phosphorus. In the broken crystal composition is in agreement with a nominal value. For the other crystals a decrease of the gallium concentration was observed. The Nd, Ga and O line widths change. They are widest for unpolished crystal. The the XPS measurements show that etching with H3PO4 did not cause surface damage.
Moreover XPS measurements of the (011) wafer planes annealed in hydrogen atmosphere at 850-12000C were performed. There is a requirement of stability of substrate at the temperature of the growth of epitaxial layers. It was found that during the annealling processes the wafer's surfaces were covered with a white powder. The XPS measurements and chemical composition calculations for the annealed wafers show a vaporising process of Ga.


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Presentation: poster at E-MRS Fall Meeting 2003, Symposium B, by Ewa Talik
See On-line Journal of E-MRS Fall Meeting 2003

Submitted: 2003-05-23 12:33
Revised:   2009-06-08 12:55