Investigation of Photoexcited Carrier Dynamics in Hematite and the Effect of Surface Modifications by an Advanced Transient Grating Technique.

Photoexcited carrier dynamics in a hematite film with and without amorphous NiFeO on the surface was investigated using the heterodyne transient grating method. We found that two different electron/hole dynamics took place in the micro- and millisecond time regions and successfully assigned each component to the decay processes of electrons and holes trapped at surface states, respectively. It was also demonstrated that the amorphous NiFeO coating plays a crucial role in increasing the survival of the holes at the surface trap states, which was caused by the decrease in the surface recombination rate.