Understanding the p-Type Conduction Properties of the Transparent Conducting Oxide CuBO₂: A Density Functional Theory Analysis

Abstract

CuCrO 2 is the most promising Cu-based delafossite for p-type optoelectronic devices. Despite this, little is known about the p-type conduction mechanism of this material, with both Cu I /Cu II and Cr III /Cr IV hole mechanisms being proposed. In this article we examine the electronic structure, thermodynamic stability and the p-type defect chemistry of this ternary compound using density functional theory with three different approaches to the exchange and correlation; the generalized-gradient-approximation of Perdew, Burke and Ernzerhof (PBE), PBE with an additional correction for on-site Coulombic interactions (PBE + U) and the nonlocal, screened-exchange hybrid functional HSE06. The fundamental band gap of CuCrO 2 is demonstrated to be indirect in nature. Under all growth conditions, the dominant intrinsic p-type defect will be the Cu vacancy, with hole formation centered solely on the Cu sublattice. Mg doping is found to be significantly lower in energy than intrinsic defect formation, explaining the large increases in conductivity seen experimentally. Cu-rich/Cr-poor growth conditions are found to be optimal for both intrinsic and extrinsic (Mg doping) defect formation, and should be adopted to maximize performance.

Optical and electronic properties of delafossite CuBO2 p-type transparent conducting oxide

“…XRD peaks in the current work have been assigned according to their relationship to peak positions reported by Snure et al 9 and Santra et al 10 The lattice parameters a and c have been calculated as 2.872 and 16.580 Å , respectively, based on a hexagonal structure. These are in agreement with calculated results (a ¼ 2.53 Å and c ¼ 16.58 Å ) by Scanlon et al, 8 and experimental results (a ¼ 2.84 Å , c ¼ 16.52 Å ) by Snure et al 9 The CuBO 2 microstructure is shown in the SEM image in Fig. 2 in which the sample grain size is 1-5 lm.…”

“…E g can be obtained from a plot of (ah ) 2 vs. h , 19 by taking the intercept on the photon energy axis to zero on the (ah ) 2 axis. E g of CuBO 2 is calculated to be 3.6 eV and corresponds well with values from reports by Scanlon et al 8 and Santra et al 10 The visible light region of the electromagnetic spectrum is 1.7-3.1 eV. The energy gap for visible light transparency in materials is much larger than 3.1 eV.…”

Energy-band alignment of II-VI/Zn3P2 heterojunctions from x-ray photoemission spectroscopy

“…The HSE approach consistently produces structural and band gap data that are more accurate than standard density functional approaches, such as the local density approximation (LDA) or the generalized gradient approximation (GGA). [34][35][36][37][38][39] A cut-off value of 600 eV and a k-point mesh of 4 Â 4 Â 3, 8 Â 8 Â 6, 5 Â 5 Â 4, and 6 Â 6 Â 6, all centered on the C point, were found to be sufficient for Zn 3 P 2 , ZnO, CdS, and ZnSe, respectively. 40 All calculations were deemed to be converged when the forces on all atoms were less than 0.01 eV Å À1 .…”

Electronic structure of mixed-valence silver oxide AgO from hybrid density-functional theory

“…22 HSE has been shown repeatedly to produce structural-data and band-gap descriptions that are more accurate than LDA/GGA and meta-GGA data. [23][24][25][26][27][28][29][30][31] Cutoffs of 500 eV were used for the GGA and 400 eV was used for the more computationally expensive HSE calculations. Gamma centered k-point meshes of 4 ϫ 6 ϫ 4 were found to be sufficient for all methods.…”