Carrier dynamics in α-Fe2O3 (0001) thin films and single crystals probed by femtosecond transient absorption and reflectivity

Abstract

Femtosecond transient reflectivity and absorption are used to measure the carrier lifetimes in alpha-Fe2O3 thin films and single crystals. The results from the thin films show that initially excited hot electrons relax to the band edge within 300 fs and then recombine with holes or trap within 5 ps. The trapped electrons have a lifetime of hundreds of picoseconds. Transient reflectivity measurements from hematite (alpha-Fe2O3) single crystals show similar but slightly faster dynamics leading to the conclusion that the short carrier lifetimes in these materials are due primarily to trapping to Fe d-d states in the band gap. In the hematite single crystal, the transient reflectivity displays oscillations due to the formation of longitudinal acoustic phonons generated following absorption of the ultrashort excitation pulse.