Epitaxial growth of Cu 2 O films on MgO by sputtering
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Hyung K. Kim Department of Physics, Pusan National University, Pusan, Korea (Received 6 January 1992; accepted 30 June 1992)
The epitaxial growth of CU2O films is of significant interest for the unique potential they offer in the development of multilayer devices and superlattices. While fundamental studies may be carried out on epitaxial films prepared by any technique, the growth of artificially layered superlattices requires that films grow epitaxially during deposition. The present study examined the growth of Cu 2 O on MgO substrates directly during deposition by sputtering. Although epitaxial thin films of Cu2O could be produced, a mosaic structure was observed. The structure of the film may be related to the growth mechanism in which islands coalesce to form a continuous film.
I. INTRODUCTION Interest in Cu2O films has traditionally arisen from their photovoltaic properties and a number of studies have examined the preparation of photovoltaic cells from these films.1"4 Thin films were most commonly prepared by high- or low-temperature oxidation or by reactive sputtering. More recently, copper oxide films have attracted renewed interest based on their relationship to the recently developed high temperature superconductors.5"9 Those studies have generally concentrated on establishing the conditions under which the various oxide forms can be grown. Several of the previous studies have identified regimes in which single-phase Cu 2 O may be deposited. 1 ' 45 ' 78 In general, however, there is no consensus on the condition required for this growth. The reason for this lack of consistency is that phase selection is sensitive to the specific deposition parameters including deposition rate, true oxygen partial pressure, target temperature, etc. For example, several recent studies have shown that the deposition of these phases can be dramatically altered by the activity of the oxidant.5'6'9 The epitaxial growth of Cu2O films is of significant interest both in terms of fundamental studies that can be performed on the films themselves and for the unique potential they offer in the development of multilayer devices and superlattices. Fundamental studies may be carried out on epitaxial films prepared by any technique. The growth of artificially layered superlattices, however, requires that films grow epitaxially during deposition. A number of criteria must be satisfied in order to deposit an epitaxial Cu2O film directly from the vapor. Firstly, one must be able to deposit single phase material. In the case of reactive sputtering, this condition is not always trivial since the reaction between species during sputtering may occur at the substrate, the target, 2828
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J. Mater. Res., Vol. 7, No. 10, Oct 1992
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or in the vapor. Secondly, conditions for epitaxial growth must also be satisfied. In the classical formulation of epitaxial growth, a small mismatch is required. In a system with good lattice matching, epitaxial thin films may grow layer-by-layer or by island coal
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