First-principles investigation of interface phenomena in hafnium-based metal-insulator-metal diodes.

Metal-insulator-metal (MIM) diodes are very interesting in many different applications exploiting environment-friendly renewable energy solutions. Moreover, since the dimensions of such devices are at the nanoscale, the size and the characteristics of their constitutive elements can drastically influence their macroscale performance. As it could be difficult to describe in detail the physical phenomena occurring among materials in nanoscale systems, in this work first-principles calculations have been used to study the structural and electrical properties of three different hafnium oxide (HfO)-MIM diodes. These devices have been simulated at the atomistic level by interposing 3 nm of HfO between drain and source electrodes made of gold and platinum, respectively. The monoclinic and orthorhombic polymorphs of HfO have been considered to model different types of MIM diodes, and the interface geometries have been optimized to compute the current-voltage characteristics, reflecting the tunneling mechanisms occurring in such devices. The calculation of the transmission pathways has also been carried out to investigate the effects of atomistic coordinates despite the use of the same material. The results demonstrate the role of the Miller indices of metals and the influence of the HfO polymorphs on the MIM properties. In this study, the importance of interface phenomena on the measurable properties of the proposed devices has been investigated in detail.