Interface engineering of Ge using thulium oxide: Band line-up study

Microelectronic Engineering, Volume 109, September 2013, Pages 204-207
I.Z. Mitrovic, M. Althobaiti, A.D. Weerakkody, N. Sedghi, S. Hall, V.R. Dhanak, P.R. Chalker, C. Henkel, E. Dentoni Litta, P.-E. Hellström, M. Ostling

 

University of Liverpool, Department of Electrical Engineering & Electronics, Brownlow Hill, Liverpool L69 3GJ, UK

University of Liverpool, Department of Physics, Brownlow Hill, Liverpool L69 7ZD, UK

School of Engineering, University of Liverpool, Brownlow Hill, Liverpool L69 3GH, UK

KTH Royal Institute of Technology, School of ICT, Electrum 229, SE-164 40 Kista, Sweden

 

 

Abstract

This paper investigates the band line-up and optical properties (dielectric function) of Tm2O3/Ge gate stacks deposited by atomic layer deposition. X-ray photoelectron spectroscopy has been performed to ascertain the shallow core levels (Ge3d and Tm4d) in ultra-thin and bulk Tm2O3/Ge stacks as well as valence band maxima in Ge and bulk Tm2O3. The valence band offset of Tm2O3/Ge has been found to be 2.95 ± 0.08 eV. Vacuum ultra violet variable angle spectroscopic ellipsometry studies reveal the indirect band gap nature of Tm2O3, with the value extracted from the Tauc method of 5.3 ± 0.1 eV. A distinct absorption feature is observed at ∼3.2 eV below the band gap of Tm2O3, and clearly distinguished from the Si and Ge critical points. A dielectric constant of 14 to 15 has been derived from the electrical measurements on 5 nm Tm2O3/epi Ge/Si gate stacks. The band line-up study of Tm2O3/Ge implies an acceptable barrier for holes (2.95 eV) and electrons (greater than 1.7 eV) for Ge MOSFET engineering.

 

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