Hexagonal to monoclinic phase transformation in Eu2O3 thin films grown on GaN (0001)

Abstract

The high-pressure hexagonal phase of Eu2O3 has been grown epitaxially on C-plane GaN (0001) by molecular beam epitaxy. A structural phase transition from the hexagonal to the monoclinic phase is observed with increasing film thickness by ex-situ X-ray diffraction. The critical thickness for the structural transition is between 2 and 6 nm. The observed epitaxial relationships between the substrate and the film are GaN (0001) ǁ Eu2O3 (0001), GaN ⟨112¯0⟩ ǁ Eu2O3 ⟨112¯0⟩ for the hexagonal phase, and GaN (0001) ǁ Eu2O3 (201¯), GaN ⟨112¯0⟩ ǁ Eu2O3 [020] with six rotational domains for the monoclinic phase. The (0.8 ± 0.2) eV conduction band offset and bulk dielectric constant of ∼14 makes Eu2O3 a possible gate dielectric for a GaN-based field effect transistor.

Programmable Polarization of 2D Anisotropic Rare Earth Material for Images Transmission and Encryption

“…[ 26 ] Clearly, the height of a single Eu 2 O 3 unit cell is about 0.36 nm along the b ‐axis. [ 27 ] With CVD methods, the rectangular Eu 2 O 3 flake with size ≈20 µm were obtained shown in Figure S2a (Supporting Information). The thickness of Eu 2 O 3 flakes can be as thin as ≈4.7 nm (Figure S2b, Supporting Information).…”

Evidence for the Eu 4f Character of Conduction-Band Edge at the Eu2O3 Surface Studied by Scanning Tunneling Spectroscopy

“…The experiments were performed in two separate ultra-high vacuum (UHV) systems. The Eu 2 O 3 film was grown on GaN(0001)/p-Si(111) substrates at 800 o C by MBE; the growth, sample and UHV system details are described in [1,4].The Eu 2 O 3 film revealed a streaky reflection high-energy electron diffraction (RHEED) pattern after formation, as shown in Figure 1. The rotational symmetry of the pattern was 6-fold, the same as the underlying GaN susbstrate pattern.…”

“…For europium oxide three major forms exist: EuO, Eu 3 O 4 , and Eu 2 O 3 . The Eu atoms in the sesquioxide (Eu 2 O 3 ) have the highest possible oxidation state (+3), and therefore, during synthesis the stoichiometry of this form can be precisely achieved under oxygen-rich conditions [1]. Having a dielectric constant of about 14 [2] and a measured band gap of ~4.3-4.4 eV [3,4], Eu 2 O 3 is considered to be attractive as a high-K gate dielectric [5].…”