Lone-Pair Stabilization in Transparent Amorphous Tin Oxides: A Potential Route to p-Type Conduction Pathways

Abstract

The electronic and atomic structures of amorphous transparent tin oxides have been investigated by a combination of X-ray spectroscopy and atomistic calculations. Crystalline SnO is a promising p-type transparent oxide semiconductor due to a complex lone-pair hybridization that affords both optical transparency despite a small electronic band gap and spherical s-orbital character at the valence band edge. We find that both of these desirable properties (transparency and s-orbital valence band character) are retained upon amorphization despite the disruption of the layered lone-pair states by structural disorder. We explain the anomalously large band gap widening necessary to maintain transparency in terms of lone-pair stabilization via atomic clustering. Our understanding of this mechanism suggests that continuous hole conduction pathways along extended lone pair clusters should be possible under certain stoichiometries. Moreover, these findings should be applicable to other lone-pair active semiconductors

Band edge evolution of transparent ZnM2IIIO4 ( MIIWahila1, Lebens-Higgins2, Jackson3 et al. 2019Phys. Rev. BSelf Cite16180View full textAdd to dashboardCite

“…These findings explain the observation of both n-and ptype conduction in ZnCo 2 O 4 [17]. A small electronic band gap with forbidden optical transitions between the true band edges allows for both the observed doping capabilities and the high optical transparency, similar to some other transparent metal oxides such as crystalline SnO or CuInO 2 [8,48,49]. Furthermore, the increased conductivity of crystalline ZnRh 2 O 4 and ZnIr 2 O 4 relative to ZnCo 2 O 4 [30] is explained by the observed increase in hybridization at the band edges for these M III cations.…”

“…In contrast, p-type conduction in these oxides is typically poor due to their localized O 2p-derived valence band maxima. However, hybridization between the O 2p and metal orbitals has been shown to improve hole dispersion, as in some Cu + -based delafossites, Cr 3+based oxides, and post-transition-metal oxides with a filled lone pair state (ns 2 ) [5][6][7][8][9][10]. Unfortunately, some common theoretical methods are known to be unreliable when predicting the properties of mixed oxides with potentially complex local interactions [11], hampering computation-led materials genome initiatives that exist to accelerate the discovery of these materials.…”

Electroactive Nanoporous Metal Oxides and Chalcogenides by Chemical Design

“…These p-orbitals are orientated into the pores and thus do not form a continuous pathway in the framework of the structure for charge transport; similar obstacles to hole mobility are often encountered in amorphous oxides. 42 …”

Computational Screening of All Stoichiometric Inorganic Materials

“…The electronic density of states reveals an upper valence band composed of hybridized Sn s – Cl p orbitals; such Sn s -based valence bands are considered promising indicators for hole mobility. 42 The lower conduction band is composed mainly of overlapping Sn p orbitals. The chemical structure and bonding characteristics suggest that this material should have favorable carrier transport, crucial for optoelectronic applications.…”