Biaxial Stress-Induced Giant Bandgap Shift In Bifeo3 Epitaxial Films

Thickness-dependent stress relaxation and its influence on the bandgap of BiFeO3 have been investigated. BiFeO3 films with 15 at% Bi excess allow the control of lattice mismatch-induced biaxial stress up to 10.8 GPa on SrTiO3(001) substrates. Heteroepitaxy of such films follows the Stranski-Krastanov growth mode, as suggested by island formation on the wetting layer accompanied with stress relaxation. The bandgap is linearly decreased with the in-plane compressive stress, and a large stress coefficient of 67 meV/GPa was extracted. A 0.7 eV red-shift of the bandgap was observed in the fully epitaxially strained film. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim