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

We have measured the valence-band discontinuity at artificially structured, epitaxial heterojunctions of alpha-Cr2O3(0001) and alpha-Fe2O3(0001). Laye red film structures of these two materials maintain the in-plane lattice pa rameter 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) laye rs 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 al pha-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 noncommutativ ity in the band offset is not due to either anisotropic strain or quantum c onfinement, but rather appears to be due to a growth-sequence-dependent int erface dipole.