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We investigate the various cation substitutional dopants in Ga2O3 for the possibility of p–type conductivity using density functional theory. Our calculations include both standard density functional theory and hybrid functional calculations. We demonstrate that all the investigated dopants result in deep acceptor levels, not able to contribute to the p–type conductivity of Ga2O3. In light of these results, we compare our findings with other wide bandgap oxides and reexamine previous experiments on zinc doping in Ga2O3.

We report inelastic x-ray scattering studies of charge excitations in insulating Nd 2 CuO 4 as a function of incident photon energy. An excitation of ϳ6 eV is observed when the incident photon energy is tuned through the Cu K edge. This is interpreted as resonantly enhanced inelastic x-ray scattering. Numerical calculations identify the 6 eV feature as a charge-transfer excitation to the antibonding state and suggest that nonlocal effects play a role in determining the shape of the resonance. [S0031-9007(98)06181-X] PACS numbers: 74.25.Jb, 71.27. + a, Understanding the normal state electronic properties of the high-T C copper oxides is an important prerequisite for a theory of high temperature superconductivity. In addition, the properties themselves are highly unusual, exhibiting non-Fermi-like behavior [1] and they have therefore attracted much interest from the more general perspective of understanding electronic behavior in strongly correlated transition metal oxides.A useful theoretical approach has been to treat the copper oxide planes within the framework of a microscopic electronic Hamiltonian, such as the extended Hubbard model [2]. The strong electron correlations preclude the possibility of successful band structure calculations, and a variety of numerical techniques have therefore been applied, utilizing small clusters of ions for which on-site interactions can be treated explicitly [3], for example, impurity and cluster interaction models [4,5]. These models are typically local, that is, the translational symmetry of the lattice is neglected. However, as first emphasized by Veenendaal, Eskes, and Sawatzky [6], solid state (nonlocal) effects can be important, and recently calculations have been performed for a number of clusters connected in a planar geometry for which some degree of translational symmetry is restored [7].A crucial test of such treatments is to compare their predictions with measurements of the electronic excitation spectrum. To this end a variety of spectroscopies have been applied to the cuprates. However, each has its limitations. For example, photoemission experiments only probe to the photoelectron escape depth and it can be difficult to ensure that bulklike properties are measured. Also finalstate effects (i.e., those due to the presence of a core hole in the final state) are large, and electrostatic charging may be a problem for insulators. X-ray absorption spectroscopy (XAS) offers bulklike penetration, but still suffers from a final-state core hole, and optical spectroscopies are essentially limited to q 0 properties and energy transfers of a few eV. There remains a clear need for new spectroscopies to elucidate the electronic excitation spectrum of the high-T C cuprates.Inelastic x-ray scattering in the hard x-ray regime exhibits none of the above disadvantages. The scattering process is charge neutral so that final-state effects are eliminated and the excitation spectrum is measured directly. Further, bulklike properties are measured. It would thus seem an ideal tool in thi...