Prediction and realisation of high mobility and degenerate p-type conductivity in CaCuP thin films

Joe Willis; Ivona Bravić; Rekha R. Schnepf; Karen N. Heinselman; Bartomeu Monserrat; Thomas Unold; Andriy Zakutayev; David O. Scanlon; Andrea Crovetto

doi:10.1039/D2SC01538B

Prediction and realisation of high mobility and degenerate p-type conductivity in CaCuP thin films†

Joe Willis,

^abc Ivona Bravić,^d Rekha R. Schnepf,^ef Karen N. Heinselman,

^e Bartomeu Monserrat,

^dg Thomas Unold,

^h Andriy Zakutayev,

*^e David O. Scanlon

*^ab and Andrea Crovetto

‡*^eh

Author affiliations

* Corresponding authors

^a Department of Chemistry, University College London, 20 Gordon Street, London, UK
E-mail: d.scanlon@ucl.ac.uk

^b Thomas Young Centre, University College London, Gower Street, London, UK

^c Diamond Light Source Ltd, Harwell Science and Innovation Campus, Didcot, Oxfordshire, UK

^d Theory of Condensed Matter Group, Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge, UK

^e National Renewable Energy Laboratory, Golden, Colorado 80401, USA
E-mail: andriy.zakutayev@nrel.gov, ancro@dtu.dk

^f Department of Physics, Colorado School of Mines, Golden, Colorado 80401, USA

^g Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge, UK

^h Department of Structure and Dynamics of Energy Materials, Helmholtz-Zentrum Berlin für Materialien und Energie, GmbH, Berlin, Germany

Abstract

Phosphides are interesting candidates for hole transport materials and p-type transparent conducting applications, capable of achieving greater valence band dispersion than their oxide counterparts due to the higher lying energy and increased size of the P 3p orbital. After computational identification of the indirect-gap semiconductor CaCuP as a promising candidate, we now report reactive sputter deposition of phase-pure p-type CaCuP thin films. Their intrinsic hole concentration and hole mobility exceed 1 × 10²⁰ cm⁻³ and 35 cm² V⁻¹ s⁻¹ at room temperature, respectively. Transport calculations indicate potential for even higher mobilities. Copper vacancies are identified as the main source of conductivity, displaying markedly different behaviour compared to typical p-type transparent conductors, leading to improved electronic properties. The optical transparency of CaCuP films is lower than expected from first principles calculations of phonon-mediated indirect transitions. This discrepancy could be partly attributed to crystalline imperfections within the films, increasing the strength of indirect transitions. We determine the transparent conductor figure of merit of CaCuP films as a function of composition, revealing links between stoichiometry, crystalline quality, and opto-electronic properties. These findings provide a promising initial assessment of the viability of CaCuP as a p-type transparent contact.

This article is part of the themed collections: Most popular 2022 physical and theoretical chemistry articles and 2022 Chemical Science HOT Article Collection

Chemical Science

Prediction and realisation of high mobility and degenerate p-type conductivity in CaCuP thin films†

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Prediction and realisation of high mobility and degenerate p-type conductivity in CaCuP thin films

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