Abstract
Semiconducting KTaO3 single crystals have been investigated as a model potential photoanode for hydrogen production using photoelectrochemical (PEC) cells. In order to modify the electronic properties of KTaO3 by reducing the bandgap and thereby increase the absorption of light at longer wavelengths, KTaO3 single crystals were doped during the crystal growth process. A wide range of dopant elements was employed that consisted primarily of transition metals - due to the established effects they have exhibited in modifying the properties of other semiconducting systems such as TiO2. With the exception of the crystals grown with LiCO3 or B2O3 added to the melt (resulting in crystals that were not effectively doped), the crystals exhibited n-type behavior with carrier concentrations ranging from 4 x 1018 to 2.6 x 1020 cm-3. The position of the band edges indicated that the crystals were thermodynamically capable of water dissociation without the application of an external bias. External quantum yield (QY) measurements revealed that the samples were photoactive up to a wavelength of ~350 nm. Higher QY�s were measured when some of the crystals were thermochemically treated in a CO atmosphere. The indirect bandgap and a parameter denoted as E1 that is related to the direct band edge of the semiconductor were found to be the same within the statistical error for all the samples. These results indicate that the various dopants and treatments did not produce changes in the KTaO3 electronic structure that were sufficient to significantly modify the behavior exhibited by this material in a PEC cell.
