In this work, we report on the epitaxial growth of multiferroic on GaN. Both materials are hexagonal with a nominal lattice mismatch of 4%, yet x-ray diffraction reveals an unexpected 30° rotation between the unit cells of and GaN that results in a much larger lattice mismatch (10%) compared to the unrotated case. Estimates based on first principles calculations show that the bonding energy gained from the rotated atomic arrangement compensates for the increase in strain energy due to the larger lattice mismatch. Understanding the energy competition between chemical bonding energy and strain energy provides insight into the heteroepitaxial growth mechanisms of complex oxide-semiconductor systems.
The scan was performed on a diffractometer without sample tilt perpendicular to the beam ( angle), resulting in unequal intensities for symmetry related peaks.
In our model, the GaN is Ga terminated, and the subsequent layers are an apical oxygen layer of followed by either a MnO layer or a Y layer. Bonding is assumed to occur between the Ga surface atoms and the apical oxygen layer of . The formation of the interface then results from a competition between elastic strain and Ga–O bond formation in the first deposited layer.
The strain was defined with respect to the experimentally observed in-plane spacing of .