Epitaxial growth and structure of the high-k dielectric Pr$_{2}$O$_{3}$ on Si(001) and Si(111)

Keeping the capacitance of CMOS devices constant while shrinking further the gate dimensions requires intolerably thin SiO$_{2}$ layers for next generation devices. Thus, replacing SiO$_{2 }$with a material with larger static permittivity k and matching properties is at present a very urgent task. Among others, the sesquioxide Pr$_{2}$O$_{3}$ is discussed as a possible candidate material. We deposited ultra thin films of Pr$_{2}$O$_{3 }$by e-beam evaporation$_{ }$on atomically clean (001) and (111) surfaces. We studied the growth from the very early stages using low energy electron diffraction, scanning tunneling microscopy, Auger electron spectroscopy, grazing incidence X-ray diffraction, X-ray reflectivity and X-ray photoelectron spectroscopy. On Si(111), Pr$_{2}$O$_{3 }$grows pseudomorphically in the hexagonal phase. On Si(001) surface, a 0.6 nm thick layer of cubic Pr$_{2}$O$_{3 }$ grows followed by the formation of a silicate layer on top. Growth under 10$^{-8}$ mbar O$_{2}$ atmosphere is needed in order to prevent Pr-silicide formation.