Metallicity at interphase boundaries due to polar catastrophe induced by charge density discontinuity

Abstract

The electronic properties of interphase boundaries are of basic importance for most materials, particularly when those properties deviate strongly from the bulk behavior. We introduce a mechanism that can result in metallicity at stoichiometric interphase boundaries between semiconductors based on the idea of polar catastrophe, which is usually considered only in the context of heterostructures. To this end, we perform ab initio calculations within density functional theory to investigate the electronic states at stoichiometric SnO/SnO 2 (110) interphase boundaries. In this system, one would not expect polar catastrophe to have a role according to state-of-the-art theory because the interface lacks formal charge discontinuity. However, we observe the formation of a hole gas between the semiconductors SnO and SnO 2 . To explain these findings, we provide a generalized theory based on the idea that the charge density discontinuity between SnO and SnO 2 , a consequence of lattice mismatch, drives a polar catastrophe scenario. As a result, SnO/SnO 2 (110) interphase boundaries can develop metallicity depending on the grain size. The concept of metallicity due to polar catastrophe induced by charge density discontinuity is of general validity and applies to many interphase boundaries with lattice mismatch.

Density Functional Theory Study of Two-Dimensional Post-Transition Metal Chalcogenides and Halides for Interfacial Charge Transport in Perovskite Solar Cells

“…along the c-axis 40 . In the layered SnO crystal structure, each Sn atom is linked to four O atoms and vice versa 41,42 , see Figure 1 (e-f).…”

Charge-transfer interface of insulating metal-organic frameworks with metallic conduction

“…Typically, in TMOs, positively charged transition metal ion is coordinated to six negatively charged oxygen ions and thereby creating an octahedral crystal field around the metal ion, which lifts the five-fold degeneracy of the d -orbitals. Polar nature of the metal-oxygen bonds in combination with non-zero amplitude of the hopping matrix across an interface makes the correlated-electron behavior exotic when compared to the same in the bulk-phase—often leads to polar-catastrophe at the interfaces 9 – 11 . As for the organic molecules, metallic conduction at the interface was also realized though individual molecular counterparts in the respective bulk phases were found to be electrical insulators with band gap values of few electron volts 12 .…”