Interplay between Composition, Electronic Structure, Disorder, and Doping due to Dual Sublattice Mixing in Nonequilibrium Synthesis of ZnSnN₂:O

Abstract

The opportunity for enhanced functional properties in semiconductor solid solutions has attracted vast scientific interest for a variety of novel applications. However, the functional versatility originating from the additional degrees of freedom due to atomic composition and ordering comes along with new challenges in characterization and modeling. Developing predictive synthesisstructure-property relationships is prerequisite for effective materials design strategies. Here, we present a first-principles based model for property prediction in such complex semiconductor materials. This framework incorporates non-equilibrium synthesis, dopants and defects, and the change of the electronic structure with composition and short range order. This approach is applied to ZnSnN 2 (ZTN) which has attracted recent interest for photovoltaics. The unintentional oxygen incorporation and its correlation with the cation stoichiometry leads to the formation of a solid solution with dual sublattice mixing. We uncover a non-monotonic doping behavior as function of This article is protected by copyright. All rights reserved. 2 the composition, and the degenerate doping of near-stoichiometric ZTN, which is detrimental for potential applications, can be lowered into the 10 17 cm -3 range in highly off-stoichiometric material, in quantitative agreement with experiments.

Rapid Development of Disruptive Photovoltaic Technologies

“…We theoretically explained that the carrier density in ZnSnN2 decreases to 10 17 cm -3 with increasing Zn and O content due to formation of defect complexes and modification of the material electronic structure. 13 Further, we experimentally showed that annealing Zn1+xSn1-xN2 grown with added hydrogen reduces its free electron density by orders of magnitude, down to 4 × 10 16 cm -3 . 14 These carrier densities are low enough for formation of rectifying heterojunctions necessary for solar cell fabrication, according to modeling.…”

“…To explain the unusual ZTN material properties, we developed an approach to go beyond the conventional defect model by considering the additional effects of non-equilibrium synthesis, off-stoichiometry, disorder, and (intentional or unintentional) incorporation of impurities, thereby capturing the physics of non-ideal complex mixed-ion semiconductor materials. 13 The ZTN calculations results ( Fig.1) show that the net doping is a non-monotononic function of the Zn and O content, which has been considered as anomalous/unusual in the past. The non-monotonic behavior is mainly due to the composition induced changes in the electronic structure, namely change in the band position and the resulting change in defect formation enthalpies at high Zn and O content.…”

Electron scattering mechanisms in polycrystalline sputtered zinc tin oxynitride thin films

“…Defect equilibrium, by accounting for both defect and defect pair binding, was obtained by solving the self-consistent equation by forcing the charge neutrality between free carriers and charged defects. 10,24,25 Since the carrier concentration depends on the relative distance of Fermi level to the band edges, oxygen induced band edge shifts were also included in the defect equilibrium simulation. 10 At T ¼ 700 K, the defect equilibrium calculation was conducted as a function of oxygen content under Zn-rich conditions (Zn 3 N 2 limit).…”

“…10,24,25 Since the carrier concentration depends on the relative distance of Fermi level to the band edges, oxygen induced band edge shifts were also included in the defect equilibrium simulation. 10 At T ¼ 700 K, the defect equilibrium calculation was conducted as a function of oxygen content under Zn-rich conditions (Zn 3 N 2 limit). Two defect pairs, (Zn Sn ÀO N ) À and (Zn Sn À2O N ) 0 , play important roles with the pair binding energies about À0:97 eV and À1:73 eV, respectively, relative to the isolated Zn 2À Sn and O þ N defects.…”

“…9 To explain these exciting and surprising results, a theoretical model has been developed, including the effects of nonequilibrium synthesis; dopants, defects, and complexes; and the change of the electronic structure with composition and short range order. 10 This model explains that at dilute concentrations in ZnSnN 2 , oxygen acts as an n-type dopant in the form of O þ N point defects contributing to the degeneracy of ZnSnN 2 :O films. However, as oxygen content increases above 2%, the dilute defect model breaks down due to most of the O þ N defects being compensated by Zn Sn defects effectively coupling the O/N and Zn/Sn stoichiometry.…”