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Polaronic interacceptor hopping transport in intrinsically doped nickel oxide

Robert Karsthof, Marius Grundmann, Arthur Markus Anton, and Friedrich Kremer
Phys. Rev. B 99, 235201 – Published 20 June 2019

Abstract

In this work, we revisit the issue of the nature of electronic transport in nickel oxide (NiO) and show that the widely used model of free small polaron hopping, initially raised to characterize transport in high-purity samples, is not appropriate for modeling intrinsically doped NiO. Instead, we present extensive evidence, collected by means of temperature- and frequency-dependent measurements of the electrical conductivity σ, that the model of polaronic interacceptor hopping can be used to consistently explain the electronic conduction process. In this framework, holes are localized to acceptors (Ni vacancies), forming a strongly bound, polaron-like state. They can only move through the film by hopping to a neighboring, at least partially unoccupied, acceptor. This renders the spatial overlap between neighboring polaronic wave functions a highly critical parameter. The signature of this process is the occurrence of two temperature regions of the dc conductivity, separated by about half the Debye temperature θD2200K. For T>θD2, holes are transferred by phonon-assisted hopping over the potential barrier between two sites, whereas phonon-assisted tunneling through the barrier dominates below that temperature. We also show that the degree of structural and electronic disorder plays a vital role in determining the characteristics of the transport process: high disorder leads to strong energetic broadening of the acceptor states such that hopping to more distant sites may be favored over transfer to nearest neighbors (variable range hopping). The assumption of high binding energies of the charge carriers at VNi is in accordance with the recent paradigm shift regarding the understanding of the electronic structure of NiO: holes doped into NiO couple to Ni 3d spins, thereby occupying deep polaron-like states within the band gap (Zhang-Rice bound doublets). This work explicitly takes this perception into account to explain carrier transport in NiO.

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  • Received 12 April 2019
  • Revised 24 May 2019

DOI:https://doi.org/10.1103/PhysRevB.99.235201

©2019 American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Robert Karsthof* and Marius Grundmann

  • Felix Bloch Institute for Solid State Physics, Universität Leipzig, Linnéstraße 5, 04103 Leipzig, Germany

Arthur Markus Anton and Friedrich Kremer

  • Peter Debye Institute for Soft Matter Physics, Universität Leipzig, Linnéstraße 5, 04103 Leipzig, Germany

  • *robert.karsthof@physik.uni-leipzig.de

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Issue

Vol. 99, Iss. 23 — 15 June 2019

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