Study of Scandium Based Ohmic Contacts to AlGaN/GaN Heterostructures

Grzegorz Ilgiewicz,Andrzej Stafiniak,Joanna Prazmowska-Czajka,Regina Paszkiewicz,Wojciech Macherzynski

doi:10.15598/aeee.v19i4.4134

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.

Highlights

Fabrication of ohmic contacts has few purposes
Its parameters suggest possibility of good effect on ohmic contacts parameters, there are not many studies made on scandium applicability to ohmic contacts to AlGaN/GaN heterostructures production [2]
But still only few works, present research on scandium usage in ohmic contacts production to n-GaN [2] and [3]. These suggest various behaviour of scandium contacts depending on formation temperature

Summary

Introduction

Fabrication of ohmic contacts has few purposes. One of them is to obtain as low contact resistivity as pos-There are few metals that have lower work function and should allow to fabricate ohmic contacts to used semiconductor. In process of HEMT (High Electron Mobility Transistor) fabrication, or other devices based on AlGaN/GaN heterostructure including ohmic contacts, process of deposition of additional gold layer is important. The samples with scandium including metallization formed at 425 ◦C turned out to have non-ohmic characteristics. Increase in RTP temperature of 200 ◦C reduced resistivity 1.6 times (3.52 · 10−3 Ω·cm2) but characteristics of contacts obtained at lower temperature had lower deviation from linear characteristics than in the case of sample heated to higher temperature.

Results

Conclusion