Optical vs electronic gap of hafnia by $ab\ initio$ Bethe-Salpeter equation

Benoit Sklenard (1, 2) , Alberto Dragoni (2, 1) , François Triozon (2, 1) , Valerio Olevano (3)

1 UGA [2016-2019] - Université Grenoble Alpes [2016-2019]
2 CEA-LETI - Commissariat à l'énergie atomique et aux énergies alternatives - Laboratoire d'Electronique et de Technologie de l'Information
3 NEEL - TMC - Théorie de la Matière Condensée

We present first-principles many-body perturbation theory calculations of the quasiparticle electronic structure and the optical response of HfO$_2$ polymorphs. We use the GW approximation including core electrons by the projector augmented wave method and performing a quasiparticle self-consistency also on wavefunctions. In addition, we solve the Bethe-Salpeter equation on top of GW to calculate optical properties including excitonic effects. For monoclinic HfO$_2$, we find a fundamental bandgap of $E_g$ = 6.33 eV (with the direct bandgap at $E_g^d$ = 6.41 eV) and an exciton binding energy of 0.57 eV, which situates the optical gap at $E_g^o$ = 5.85 eV. The latter is in the range of spectroscopic ellipsometry (SE) experimental estimates (5.5-6 eV), whereas our electronic bandgap is well beyond experimental photoemission (PE) estimates (< 6 eV) and previous GW works. Our calculated density of states and optical absorption spectra compare well to raw PE and SE spectra. This suggests that our predictions of both optical and electronic gaps are close to, or at least lower bounds of, the real values.

Domaines: Matière Condensée [cond-mat]

Benoit Sklenard, Alberto Dragoni, François Triozon, Valerio Olevano. Optical vs electronic gap of hafnia by $ab\ initio$ Bethe-Salpeter equation. Applied Physics Letters, 2018, 113 (17), pp.172903. ⟨10.1063/1.5044631⟩. ⟨hal-02000666⟩