Atomic-layer deposited thulium oxide as a passivation layer on germanium

I.Z. Mitrovic (1) , S. Hall (1) , M. Althobaiti (2) , D. Hesp (2) , V.R. Dhanak (2) , A. Santoni (3) , A.D. Weerakkody (1) , N. Sedghi (1) , P.R. Chalker (4) , C. Henkel (5) , E. Dentoni Litta (5) , P.-E. Hellström (5) , M. Östling (5) , H. Tan (6) , Sylvie Schamm-Chardon (6)

1 Department of Electrical Engineering and Electronics
2 Stephenson Institute for Renewable Energy
3 ENEA - Italian National agency for new technologies, Energy and sustainable economic development [Frascati]
4 University of Liverpool
5 KTH - KTH Royal Institute of Technology [Stockholm]
6 CEMES - Centre d'élaboration de matériaux et d'études structurales

A comprehensive study of atomic-layer deposited thulium oxide (Tm2O3) on germanium has been conducted using x-ray photoelectron spectroscopy (XPS), vacuum ultra-violet variable angle spectroscopic ellipsometry, high-resolution transmission electron microscopy (HRTEM), and electron energy-loss spectroscopy. The valence band offset is found to be 3.05±0.2eV for Tm2O3/p-Ge from the Tm 4d centroid and Ge 3p3/2 charge-corrected XPS core-level spectra taken at different sputtering times of a single bulk thulium oxide sample. A negligible downward band bending of ∼0.12eV is observed during progressive differential charging of Tm 4d peaks. The optical band gap is estimated from the absorption edge and found to be 5.77eV with an apparent Urbach tail signifying band gap tailing at ∼5.3eV. The latter has been correlated to HRTEM and electron diffraction results corroborating the polycrystalline nature of the Tm2O3 films. The Tm2O3/Ge interface is found to be rather atomically abrupt with sub-nanometer thickness. In addition, the band line-up of reference GeO2/n-Ge stacks obtained by thermal oxidation has been discussed and derived. The observed low reactivity of thulium oxide on germanium as well as the high effective barriers for holes (∼3eV) and electrons (∼2eV) identify Tm2O3 as a strong contender for interfacial layer engineering in future generations of scaled high-κ gate stacks on Ge. © 2015 AIP Publishing LLC.

Mots clés: Atomic layer deposition; Electron energy levels; Electron energy loss spectroscopy; Electron scattering; Energy dissipation; Energy gap; Germanium; High resolution transmission electron microscopy; Spectroscopic ellipsometry; Thulium; Core-level spectra; Differential charging; Future generations; Interfacial layer; Vacuum ultraviolets; Valence band offsets; Variable angle spectroscopic ellipsometry; X ray photoelectron spectroscopy

Domaines: Science des matériaux [cond-mat.mtrl-sci]

I.Z. Mitrovic, S. Hall, M. Althobaiti, D. Hesp, V.R. Dhanak, et al.. Atomic-layer deposited thulium oxide as a passivation layer on germanium. Journal of Applied Physics, 2015, 117 (21), pp.214104. ⟨10.1063/1.4922121⟩. ⟨hal-01720449⟩