Abstract
We report measurements of the structural, optical, transport, and magnetic properties of single crystals of the anisotropic -type transparent semiconductor . The indirect and direct band gaps are 2.97 and 3.47 eV, respectively. Temperature-dependent Hall measurements yield a positive Hall coefficient in the measured range and an activated carrier temperature dependence. The resistivity is anisotropic, with the -plane resistivity about 25 times smaller than the -axis resistivity at room temperature. Both are activated with similar activation energies. The room-temperature -plane mobility is relatively large at , and we infer a -axis mobility of . The Seebeck coefficient is positive at all measured temperatures, and has a dependence over most of the measured range. The low-temperature paramagnetic moment is consistent with a spin-1/2 defect with a density of . These results suggest that the conduction mechanism for -type carriers in is charge transport in the valence band and that the holes are thermally activated from copper-vacancy acceptor states located about 700 meV above the valence-band maximum.
1 More- Received 11 May 2009
DOI:https://doi.org/10.1103/PhysRevB.80.165206
©2009 American Physical Society