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

Abstract

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 ± 0.2 eV 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 ∼0.12 eV is observed during progressive differential charging of Tm 4d peaks. The optical band gap is estimated from the absorption edge and found to be 5.77 eV with an apparent Urbach tail signifying band gap tailing at ∼5.3 eV. 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 (∼3 eV) and electrons (∼2 eV) identify Tm2O3 as a strong contender for interfacial layer engineering in future generations of scaled high-κ gate stacks on Ge.

Band alignments of sputtered dielectrics on GaN

“…The smaller band gap values measured in this work could be due to the non-stoichiometric surface of sputtered ZrO 2 and MgO films. For Al 2 O 3 , our XPS derived band gap value of 6.48 eV is in close agreement with our previously reported value of 6.43 eV by vacuum ultra violet (VUV)-VASE [39] on MBE-deposited Al 2 O 3 , as well as the most recent theoretically predicted value of 6.36 eV [60]. A variation of reported band gap values for Al 2 O 3 can be seen in table 2, from 6.4 eV to 6.9 eV.…”

“…To account for the effect of differential charging [36,38,39], different batches of interfacial samples were prepared using RF magnetron sputtering. In the case of the oxide/semiconductor heterojunction, the positive charge generated during x-ray bombardment accumulate in the dielectrics forming the heterojunction and induce a strong modification of the kinetic energy of the emitted photoelectron.…”

“…The CBO of MgO/GaN of 2.8 ± 0.2 eV is within measurement error with the experimental value of 2.75 eV [31] and theoretically predicted value of 2.6 eV [28] as shown in table 2. Note: [15-17, 27, 29-31, 37, 45, 48, 49, 63] XPS [55] photoemission spectroscopy and XAS [44] UPS and IPS [43,46] SE [30,39] photoluminescence [28,60] theoretical CNL method.…”

(Invited) Interface Engineering Routes for a Future CMOS Ge-Based Technology

“…From Kraut's method, the VBO for Tm 2 O 3 /Ge (40) and GeO 2 /Ge (56) have been estimated to be 5.95 ± 0.08 eV and 3.45 ± 0.20 eV respectively. For the 5 nm asdeposited Tm 2 O 3 /Ge stacks, well-behaved CV characteristics have been reported (40), with the EOT of 1.28-1.43 nm and a relative permittivity of 14-15.…”

Investigation of Tm2O3 As a Gate Dielectric for Ge MOS Devices

“…Rare-earth thulium oxide (Tm 2 O 3 ) provides a high dielectric constant k~16 (5) and sufficient valence (3.05 eV) and conduction (2.05 eV) band offsets (6) for a high-k dielectric layer on Ge. In this work we investigate the effect of Tm 2 O 3 deposition on high-quality Ge/GeO 2 interfaces.…”