Epitaxial layers of insulating binary lanthanide oxides have been considered as potential alternative to conventional SiO2 for gate dielectric application in future Si-based MOSFET devices, which was investigated in more detail for epitaxial Gd2O3 and Nd2O3 as model systems. Additionally, the ability to integrate epitaxial dielectric barrier layers into Si structures can usher also in a variety of novel applications involving oxide/silicon/oxide heterostructures in diverse nanoelectronic and quantum-effect devices. Although epitaxial layers of such ionic oxides with excellent structural quality can be grown using molecular beam epitaxy, they often exhibit poor electrical properties such as high leakage current density, flat band instability, poor reliability etc. owing to the presence of electrically active charge defects, generated either during the oxide layer growth or typical subsequent CMOS process steps. Based on the origin and individual character of these defects, we review various aspects of defect prevention and passivation which lead to a significant improvement in the dielectric properties of the heterostructures. Copyright © Materials Research Society 2017