Surface recombination velocities for the (100) and (001) crystal faces of bismuth vanadate single crystals

Abstract

Bismuth vanadate (BiVO4) is widely used as a photocatalyst for water splitting, and its carrier lifetime is the most essential parameter for photocatalysts. In this study, we characterized the carrier lifetime in BiVO4 single crystals on the (100) and (001) crystal faces using the microwave photoconductivity decay (μ-PCD) method. For the (001) face, the observed μ-PCD curves with excitation by a 266 nm laser had no injected photon density dependence. In contrast, those excited using a 355 nm laser had an injected photon density dependence. The decay at a high injected photon density was faster than that at a low injected photon density. For the (100) face, the decay curves at both excitations of 266 and 355 nm were not significantly different, and they depended on the injected photon density. These results indicate that the carrier lifetime is dominated by surface recombination only under the 266 nm excitation condition for the (001) face, whereas under other conditions, this is dominated by the Schokley–Read–Hall recombination. The temperature independence of the μ-PCD curves indicates that the recombination center is sufficiently deep in the bandgap. We estimated the surface recombination velocities and bulk lifetimes of the samples by fitting the experimental results to the calculations. We believe that the estimated surface recombination velocity and bulk lifetime will aid in the design of BiVO4 photocatalysts.