The crystal structure of p-type transparent conductive oxide CuBO 2
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esearch Letters
The crystal structure of p-type transparent conductive oxide CuBO2 Tiago F.T. Cerqueira and Rafael Sarmiento-Pérez, Institut Lumière Matière, UMR5306 Université Lyon 1-CNRS, Université de Lyon, F-69622 Villeurbanne Cedex, France Fabio Trani, Institute of Theoretical Physics, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland Maximilian Amsler and Stefan Goedecker, Department of Physics, Universität Basel, Klingelbergstr. 82, 4056 Basel, Switzerland Miguel A.L. Marques and Silvana Botti, European Theoretical Spectroscopy Facility Address all correspondence to Silvana Botti at [email protected] (Received 28 March 2013; accepted 12 June 2013)
Abstract We employed ab initio global structural prediction algorithms to obtain the ground-state structure of CuBO2 This is a very promising p-type transparent conductive oxide that was synthesized recently, and thought to belong to the delafossite family. We proved that the true ground state is certainly not the delafossite structure, and that the most promising candidate is a low symmetry monoclinic phase. This is still a layered structure, but with boron and copper having a different coordination with respect to the delafossite phase.
By reporting in 1997, a transparent semiconducting material (the delafossite CuAlO2) with “reasonable” p-type conductivity, Kawazoe [1] and his co-workers opened a new era of “invisible electronics” [2] built on active devices such as diodes. This led to the opening of a variety of fields, including transparent electronics and opto-electronics, organic lightemitting diodes, integrated electro-optical (waveguide) sensors, novel solar cells, and functional smart windows. The major ingredient missing for large-scale development of such technologies is a p-type semiconductor with a large gap, high conductivities and mobilities, together with controlled transparencies that can be manufactured industrially. The most promising materials are still probably the delafossites, such as the original p-type transparent conductive oxide (TCO), CuAlO2 [1]. From all the Cu-based delafossites, CuBO2 is particularly interesting as it possesses large band gaps (direct and indirect) and higher intrinsic conductivity than any other Cu-based TCO [3]. Furthermore, it has a structure symmetry compatible with α-Al2O3 sapphire and ZnO, the latter being already widely used as n-type TCO. This last point is important for the design of a p–n junction, the initial brick of any active electrical component. CuBO2 thin films were for the first time synthesized and characterized in 2007 by Snure and Tiwari [3]. However, a theoretical work by Scanlon et al. [4] questioned the validity of the experimental lattice parameters, as they were in disagreement by more than 10% with the theoretical values obtained using either the local density approximation or the Heyid– Scuseria–Ernzerhof (HSE06) [5] functional. This result was quite unexpected, as density functional theory (DFT) calculations usually (and, in particular, for the other d
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