Dependence of the Properties of MBE-grown Multiferroic YMnO$_{3}$/GaN Heterostructures on the Growth Temperature and Post-growth Annealing Processes

We report on the molecular beam epitaxy (MBE) of multiferroic YMnO$_{3}$ on c-plane GaN. Study and understanding of these YMnO$_{3}$/GaN heterostructures are important for potential applications in multifunctional materials and structures. Atomic force microscopy revealed that the YMnO$_{3}$ films grown at different temperatures have significantly different morphologies. X-ray diffraction showed that there is a 30$^{o}$ rotation between the unit cells of YMnO$_{3}$ and GaN. Samples grown at the optimal growth temperature are ferroelectric at room temperature, with a large remnant polarization, and magnetic at low temperatures. The difference between magnetic field-cooled and zero-field-cooled behavior at low temperatures indicates the presence of antiferromagnetic frustration or ferromagnetic behavior. The effects of different growth temperatures and post-growth annealing will be discussed.