Investigation of fundamental and high order optical transitions in α-Fe₂O₃ thin films using surface barrier electroreflectance

In this paper, we use surface barrier electroreflectance technique to probe the optical transitions in hematite (α-Fe₂O₃) thin film. An electric field was induced normal to the surface of α-Fe₂O₃ thin film in an Ag/α-Fe₂O₃/Ag based capacitor type structure and the corresponding electroreflectance analysis was performed. Based on the electroreflectance analysis, we observed the fundamental as well as two high order critical points associated with α-Fe₂O₃. Standard critical point model was used to find the exact energy locations and the broadening parameters associated with these critical points. The existence of the fundamental critical point was further confirmed by the spectrophotometric analysis. The quantitative analysis based on the electro-optic energy confirmed that the obtained electroreflectance spectrum was within the low field regime, and the obtained critical points above the fundamental transition were attributed to the high order transitions of electrons from the valence band to the deep in the conduction band.