Oxide charge and band alignments in Pt/epi-Lu$_{2}$O$_{3}$/Si (111) structures studied by Internal Photoemission and C-V measurements

A variety of rare-earth/transition metal oxide films (of interest as possible ``high-k'' gate dielectrics for future MOS devices) were found to have similar band gap and band alignments to Si, and ``tailing'' conduction band (CB) states extending $\sim $1 eV below the ``primary'' CB [1]. We used internal photoemission/photoconductivity (Int-PE/PC) and capacitance-voltage (C-V) measurements to study 20 nm-thick epitaxial Lu$_{2}$O$_{3}$ film grown at 700 $^{\circ}$C on Si(111). A $\sim $1.5V difference between the oxide- and Si- flat band voltages (measured by PC and C-V respectively) indicates $\sim $6 $\times $ 10$^{12}$ cm$^{-2}$ fixed positive oxide charge, which was mostly removed by a $\sim $350 $^{\circ}$C post-metallization vacuum anneal. Int-PE measurements indicate the CB measured from the metal-side lines up $\sim $0.4 eV below the ``primary'' CB measured from the Si side, in contrast with our finding on Pt/epi-Sc$_{2}$O$_{3}$/Si (111) [2] that the metal-side CB aligned with the tail-state CB. Also, Ballistic Electron Emission Microscopy of Pt/epi-Lu$_{2}$O$_{3}$/Si (111) found $\sim $0.3 - 0.4 eV higher energy barrier than found by Int-PE, suggesting significant transient charge trapping in this sample. Work supported by NSF Grant No. DMR-0505165. [1] V. V. Afanas'ev\textit{ et al}., Appl. Phys. Lett. \textbf{85}, 5917 (2004); \textbf{88}, 032104 (2006). [2] W. Cai\textit{ et al}., Appl. Phys. Lett. \textbf{91}, 042901 (2007).