Molecular Beam Epitaxy of Rare-Earth Oxides
We present results for crystalline lanthanide oxides on silicon with the Ln2O3 composition (Ln = Pr, Nd and Gd) in the cubic bixbyite structure grown by solid state molecular beam epitaxy (MBE). On Si(001)-oriented surfaces, crystalline Ln2O3 grows as (110)-oriented domains, with two orthogonal in-plane orientations. We obtain perfect epitaxial growth of cubic Nd2O3 on Si(111) substrates. These layers can be overgrown epitaxially with silicon. The successfully demonstrated heteroepitaxy of such Si/Ln2O3/Si(111) stacks opens the door to a wide range of novel tunneling devices. For all investigated lanthanide oxides grown under ultra-high vacuum conditions, we observed the formation of crystalline interfacial silicide inclusions. MBE in combination with real-time reflection high-energy electron diffraction and in vacuo X-ray photoelectron spectroscopy were used to gain a detailed understanding of the interface and film formation during epitaxial growth of Nd2O3 on silicon. Based on that understanding, the whole growth procedure had to be adapted accordingly. In particular, the partial oxygen pressure during the interface formation and during growth is a very critical parameter. Layers grown by an appropriately by modified MBE process display no silicide inclusions, and also no interfacial silicon oxide layers.
Keywords71.55.-i; 72.80.Sk; 73.20.At; 75.47.Lx; 77.55.+f
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