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 similar to 5 to similar to 40 nm, with a relative change of similar to 20%, and saturates at a value of similar to 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.