Noncommutative band offset at α-Cr2O3/α-Fe2O3(0001) heterojunctions

We have measured the valence-band discontinuity at artificially structured, epitaxial heterojunctions of alpha-Cr2O3(0001) and alpha-Fe2O3(0001). Layered film structures of these two materials maintain the in-plane lattice parameter of alpha-Fe2O3(0001). Thus the alpha-Cr2O3(0001) layers are under a 2.4% tensile stress. A partial inward relaxation in alpha-Cr2O3(0001) layers along the c axis is also observed, revealing the presence of artifically structured epilayers with a cia ratio of 2.70, compared to 2.78 in bulk alpha-Cr2O3(0001). The valence-band offsets are -0.3 +/- 0.1 and + 0.7 +/- 0.1 eV when the top layer is Fe2O3 and Cr2O3, respectively. The noncommutativity in the band offset is not due to either anisotropic strain or quantum confinement, but rather appears to be due to a growth-sequence-dependent interface dipole.