Electronic structure and band gap of oxygen bearing c‐Zr₃N₄ and of c‐Hf₃N₄ by soft X‐ray spectroscopy

Abstract

Electronic band structures of two novel semiconducting nitrides of the group-IV elements of Th3P4-type crystal structure, c-M3N4, where M[DOUBLE BOND]Zr or Hf, is investigated using an element specific soft X-ray spectroscopy for the first time. From the pairs of N 1s X-ray absorption and N 2p [RIGHTWARDS ARROW] 1s resonant X-ray emission spectra partial densities of states (PDOS) of nitrogen, predicted to be strongly hybridized with those of the metals, are obtained for both compounds. From these data the electronic band gaps of oxygen bearing c-Zr3N4 and of c-Hf3N4, predicted before to be direct or nearly direct, are derived to be Eg = 1.6 eV and Eg = 1.8 eV, respectively. While the experimentally determined Eg for c-Hf3N4 agrees with the theoretical one obtained using the local density approximation (LDA) method, the Eg measured for oxygen bearing c-Zr3N4 is significantly higher than those calculated using both the LDA and the generalized gradient approximation method. The examined compounds, having high hardness, elastic moduli and oxidation resistance, appear to be multifunctional materials suitable also for applications as (opto)electronic materials. Band gap evolution in c-M3N4 nitrides as a function of the cation type, Zr or Hf

Tuning the Electronic Band Gap of Oxygen-Bearing Cubic Zirconium Nitride: c-Zr3–x(N1–xOx)4

“…There is one significant feature, indicated by a blue arrow, in the N 1s XAS of c -Hf 3 N 4 at ≈401.7 eV that is not reproduced by the calculation. This can be easily explained as being caused by rock salt-structured δ-HfN, which is an expected synthesis byproduct . While we did not measure directly the reference δ-HfN, Figure shows the reference spectra δ-TiN and δ-ZrN.…”

“…Their electronic structure has been extensively studied with theory, − and the theoretical electronic band gap is widely accepted to be direct and in the range of 0.7–1.8 eV . Experimentally, these materials are known to have a near-infrared electronic band gap in the range of 1.6–1.8 eV, making them a candidate for infrared light-emitting diodes (IR-LEDs). However, it is still not clear what the effect of anion substitution and cation vacancies have on the electronic structure; there are only a few experimental measurements of the electronic structure and band gap. , While these studies appear to have consistently measured electronic band gap values, they were not able to determine specifically the role anion substitution and cation defects have on both the electronic structure and the electronic band gap itself.…”

“…The tolerance of the structure of c -Zr 3– x (N 1– x O x ) 4 to significant substitution of nitrogen by oxygen, with x = 0.12 at least, is of interest due to the possibility to tune the electronic band gap by introducing substitutional oxygen into the nitrogen sites through control of the synthesis conditions . The material significance rises further if we recall its advanced or even extraordinary mechanical properties; its wear resistance exceeds by 10 times that of the industrially used TiN .…”

“…The material significance rises further if we recall its advanced or even extraordinary mechanical properties; its wear resistance exceeds by 10 times that of the industrially used TiN . The expected direct and narrow electronic band gaps of c -Zr 3– x (N 1– x O x ) 4 and c -Hf 3 N 4 make them very appealing for applications requiring LEDs because energy conversion efficiencies are controlled by the value of the exciton binding energy. − Recent soft X-ray spectroscopy measurements determined the electronic band gap of c -Zr 2.86 (N 0.88 O 0.12 ) 4 to be 1.6 ± 0.3 eV, which agreed with previous optical measurements on c -Zr 3 N 4 thin films; however, the authors did not determine the effects of lattice vacancies and substitutional oxygen on the electronic band gap making it unclear whether c -Zr 3– x (N 1– x O x ) 4 is suitable for LED applications. Moreover, neither an experimental nor a theoretical work on the exciton binding energies has been reported and the suitability of Th 3 P 4 structured nitrides for LED applications in this regard is unknown.…”

Carbides and Nitrides of Zirconium and Hafnium

“…In a 1990 review of the Hf-N system, Okamoto stated succinctly that “no information is available on the N-rich side of the diagram” [59]. Ma et al [57] computed enthalpy of formation for hypothetical ZrN 3 to be used in Calphad optimizations of the Zr-N system, but no nitrides with N/Me ratio >1 are shown on the final diagram, assessed from 500 to 5500 K. Yet, higher nitrides of Zr and Hf and Ti do exist and are the subject of intense theoretical [96,97,98,99,100,101,102,103,104] and experimental [44,46,97,105,106,107] investigations.…”