The influence of film thickness on photovoltaic effect for the Fe₃O₄/SrTiO₃:Nb heterojunctions

Fe₃O₄ films with the thickness ranging from 5 to 160 nm have been grown on SrTiO₃ : Nb (0.05wt%) substrates by the pulsed laser deposition technique. The good quality of the Fe₃O₄ film was confirmed by x-ray diffraction and magnetic analyses. It is found that the interfacial barrier of the resultant junctions, determined by the photovoltaic technique, decreases as film thickness increases from ∼5 to ∼40 nm, with a relative change of ∼20%, and saturates at a value of ∼1.2 eV above the thickness of 40 nm. Variation of lattice strains in the Fe₃O₄ film may be the reason for the thickness dependence of the interfacial barrier.