Nature of Tunable Optical Reflectivity of Rocksalt Hafnium Nitride Films

Abstract

Although the phenomenon that optical reflectivity of hard group IVB transition metal nitrides depends on stoichiometry has been reported, the microscopic origin of this behavior has not been well explored yet. Here we find that optical reflectivity of rocksalt hafnium nitride films (δ-HfN x ) can be effectively tuned by stoichiometry x, and the underlying mechanism can be well elucidated by Drude−Lorentz fitting and first-principles calculations. It is shown that the observed tunability of optical reflectivity arises from a transition from N vacancies (V N ) to Hf vacancies (V Hf ) in the films because this evolution from V N to V Hf has important roles in changing electronic properties of the films in the following three aspects: (i) density of free electrons, wherein V N and V Hf act as donor-like and acceptor-like defects, respectively; (ii) mean free path of free electrons, in which V N and V Hf are the main electron scattering sites in sub-and overstoichiometric films, respectively; (iii) interband transition absorption of bound electrons, wherein three previously unreported absorption bands originating from V N and V Hf are found to occur at ∼0.81, 2.27, and 3.75 eV. These point-defect-induced variations significantly affect the dielectric function of δ-HfN x films and thus drive the tailored evolution in reflectivity properties with x.

Pressure-stabilized hafnium nitrides and their properties

“…Three metallic Hf-vacancy nitrides, including P1-Hf 11 N 12 , P1-Hf 7 N 8 and C 2/m-Hf 4 N 5 are stable at 0 GPa, consistent with the stoichiometries proposed by experiments of Hf-vacancies containing in HfN x film (x > 1) [9,10]. The ground-state phase we find for Hf 3 N 4 is not the orthorhombic Zr 3 N 4 -type (Pnma) which was proposed [15,19] (Fig.…”

“…Among them, hafnium nitrides (HfN x ), display high melting points (HfN: 3330 ℃ [1]), high incompressibility (HfN: B 0 =260-306 GPa [2]; Hf 3 N 4 : B 0 = 227-260 GPa [3,4]), oxidation resistance at high temperature [5] and superconductivity (HfN: T c =8.8 K) [6], and have been widely exploited by experiments [7][8][9][10] and calculations [8][9][10][11] in recent years.…”

Plasma-Assisted ALD of Highly Conductive HfNx: On the Effect of Energetic Ions on Film Microstructure

“…HfN x predominantly exists in two crystal phases: highly resistive Hf 3 N 4 with Hf(IV) oxidation state [9,10], and low resistivity δ-HfN with Hf(III) oxidation state [11,12]. The control of the oxidation state of Hf is therefore essential to synthesize conductive HfN x layers [13][14][15].…”

“…The control of the oxidation state of Hf is therefore essential to synthesize conductive HfN x layers [13][14][15]. Physical vapor deposition (PVD) methods have been widely adopted for the synthesis of low resistivity HfN x films [8,11,12,[16][17][18][19]. Seo et al have reported the growth of stoichiometric and epitaxial 500 nm thick HfN x layers with a resistivity of 1.4 × 10 -5 Ωcm, which is the lowest resistivity value reported thus far [18].…”

Plasma-assisted atomic layer deposition of HfNx: Tailoring the film properties by the plasma gas composition

“…Two envisioned applications are the combination of HfO 2 with HfN as gate dielectric and gate metal in a MOS configuration as reported by Yu et al 1,5 and HfN as back reflector electrode for copper-indium-gallium-selenide solar cells, due to its high reflectivity (>85%) in the low energy photon region (1 eV E 2.4 eV) for semi-infinite films. [6][7][8] Both applications require low resistivity of HfN layers (q ¼ 10…”