Study of Scandium Based Ohmic Contacts to AlGaN/GaN Heterostructures

Abstract

Development of semiconductor devices based on AlGaN/GaN heterostructure requires study and improvement of ohmic contacts, whose necessary improvement lies in process of checking new metallic compositions and thermal formation process parameters. Usually, in metallic ohmic annealed contacts of AlGaN/GaN heterostructures, titanium is applied as the first layer, but scandium may be an alternative. It was proved to be useful to obtain both ohmic and Schottky characteristics, depending on annealing temperature of the contact. In the presented research, contacts including scandium (Sc/Al/Mo/Au) were fabricated, and, as reference sample, contacts with titanium including metallziation (Ti/Al/Mo/Au). Reference sample was annealed at 825 ◦C, and forming temperatures for scandium contacts were 825 ◦C, 625 ◦C, and 425 ◦C. All samples after thermal formation process were additionally thickened with Ru/Au bilayer. To quickly compare level of metals in metallization mixing during formation process and to check applicability of EDS (Energy-Dispersive X-ray Spectroscopy), the simulations of electrons trajectories and EDS point scans were performed.