Uncovering Photo-Excited Charge Carrier Dynamics in Hematite (α-Fe2O3) Hidden in the Nanosecond Range by the Heterodyne Transient Grating Technique Combined with the Randomly Interleaved Pulse-Train Method

Photo-excited charge carrier dynamics in hematite (alpha-Fe2O3), ranging from 10(-8) to 10(-5) s, was investigated using the heterodyne transient grating technique in combination with the randomly interleaved pulse-train method. We observed four components in this time scale, and each component was successfully assigned by scavengers and the responses of oxygen-abundant and -deficient samples were compared. Particularly, we found components which have not been discussed so far with an aid of the combination method, and they were assigned to recombination arising from trapped electrons. In addition, the effect of an amorphous NiFeOx coating on the dynamics in this time scale was also investigated under the bias condition and demonstrated that the coated sample strongly depended on the applied bias voltage, while the bare sample did not, implying that the Fermi-level pinning effect in hematite was reduced by the amorphous NiFeOx coating.