Atomic-layer deposited thulium oxide as a passivation layer on germanium
Résumé
A comprehensive study of atomic-layer deposited thulium oxide (Tm2 O3 ) 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 Tm2 O3 /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 Tm2 O3 films. The Tm2 O3 /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 Tm2 O3 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
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