Modeling the polaronic nature of p-type defects in Cu2O: The failure of GGA and GGA plus U
Citation:Scanlon, DO, Morgan, BJ, Watson, GW, Modeling the polaronic nature of p-type defects in Cu2O: The failure of GGA and GGA plus U, JOURNAL OF CHEMICAL PHYSICS, 131, 2009, 124703
Cu2O JCP.pdf (Published (publisher's copy) - Peer Reviewed) 282.8Kb
Cuprous oxide (Cu2O) is an abundant, low cost, nontoxic semiconductor material with a direct band gap of 2.17 eV.1 Interest in this prototypical p-type conducting oxide is due to its potential use for photovoltaic powercell applications2 and as a possible p-type host for dilute semiconductor ferromagnetism when doped with magnetic ions.3 The recent explosion of interest in p-type transparent conducting oxides (TCOs) such as CuMO2 (M = Al, Cr, B, Ga, In) (Ref. 4) and SrCu2O2 (Ref. 5) has also refocused attention on the chemistry of Cu(I) oxides, as the p-type properties of these materials are thought to be similar.6 p-type conduction in Cu2O is caused by oxygen excess, which results in the formation of hole (acceptor) states above the valence band.6 The valence bands of most wide band gap metal oxides are composed of O?2p states, leading p-type doping to often result in localized oxygen holes deep in the band gap, associated with poor p-type conduction. In Cu2O, the top of the valence band is dominated by Cu?3d states, with some O?2p mixing.7 Upon hole formation, oxidation of 3d10 Cu(I) to 3d9 Cu(II) occurs, with the corresponding acceptor levels being formed primarily on the Cu?d states.8 The band gap of Cu2O is not sufficiently large for transparency in the visible spectrum (band gaps greater than 3.1 eV ensure transparency), making Cu2O itself unsuitable for TCO applications. The small band gap is thought to be due to the three-dimensional interactions between 3d10 electrons on neighboring Cu(I) ions.9 These three-dimensional interactions are a consequence of the crystal structure, which can be constructed as two interpenetrating cristobalite lattices,10,11 as shown in Fig. 1. It was proposed by Kawazoe et al. that maintaining the p-type nature of Cu2O is necessary for the development of Cu-based p-type TCOs, and this was incorporated in a set of design rules for TCOs, called the ?chemical modulation of the valence band.?12 This approach aims to maintain the valence band properties of Cu2O while increasing the band gap by alloying with other oxides, such as Al2O3 or SrO, to form CuAlO2 or SrCu2O2, respectively. These ternary oxides decrease the dimensionality of the Cu?Cu interactions, resulting in band gaps large enough for TCO applications.5,13,14 The defect chemistry of Cu2O and these technologically useful daughter compounds is expected to be similar; thus developing an understanding of the p-type behavior of Cu2O is an important step toward understanding the chemistry of Cu-based TCOs.
Science Foundation Ireland (SFI)
Type of material:Journal Article
Series/Report no:JOURNAL OF CHEMICAL PHYSICS
Availability:Full text available