Band-gap narrowing in α-(CrxFe1-x)2O3 solid-solution films

We report on structural and optical properties for the (0001)-oriented alpha-(CrxFe1-x)(2)O-3 (0 <= x <= 1) epitaxial films prepared on c-sapphire substrates by using pulsed-laser deposition. Pure corundum phase with atomically flat surface was obtained in the entire composition range. Optical absorption spectra for the films with 0.2 < x < 0.9 showed a nearly constant band-gap (1.7 eV), which is narrower than those of alpha-Fe2O3 (2.1 eV) and alpha-Cr2O3 (3.0 eV). The result suggests that the band-gap narrowing arises from a type-II band alignment of these oxides and the fundamental band-gap lies between the Cr t(2g) and O 2p occupied states and the Fe t(2g)* empty state. (C) 2011 American Institute of Physics. [doi:10.1063/1.3669704]