Measurement of transient photoabsorption and photocurrent of BiFeO_3 thin films: Evidence for long-lived trapped photocarriers

We have studied the optical response and dynamical behavior of photocarriers in BiFeO3 thin films by means of transient absorption (TA) and photocurrent (PC) measurements. PC and absorption spectroscopy indicate that BiFeO3 thin films have an indirect band gap energy of ∼2.4 eV. The TA and PC decay dynamics have fast (∼1 ns) and slow (∼100 ns) components that are attributed to the localization of free carriers to shallow trap states and the recombination of trapped carriers, respectively. The long decay time of the PC is caused by the thermal activation of trapped carriers into the conduction band. Long-lived trapped photocarriers can be linked to the ferroelectricity and give rise to unique photoinduced phenomena in BiFeO3