Development of ohmic contacts for GaN-based vertical power devices

Oskar Sadowski

supervisor: Mariusz Sochacki

Due to the limited availability of good-quality, large-diameter monocrystalline GaN substrates, the development of vertical devices has been limited for many years. The first working devices have been demonstrated only in recent years. The improvement of device parameters and demonstration of the possibilities resulting from the excellent electrophysical properties of GaN still requires intensive construction and technological works.

In first semester of my doctoral studies, I was working on ohmic contacts to p-type epitaxial GaN layer. The fabrication of low-resistive ohmic contacts for p-GaN is still a challenge, and the achieved resistivities rarely fall below 1x10^-4 Ωcm².

In order to optimize the contact to p-type GaN the samples with metal contacts containing Ni, Au and Pd were prepared and characterized. The investigation include different metal deposition methods, different thickness of metallic layers, different semiconductor surface preparation methods and different annealing temperatures and atmosphere. The resistivity of ohmic contacts was estimated by circular transmission line method (cTLM). The best result obtained in this series of experiments was 5x10^-5 Ωcm².

This work was partially supported by The National Centre for Research and Development under Agreement nr TECHMATSTRATEG-III/0003/2019 for project "Complete vertically integrated technological chain for vertical GaN-on-GaN power electronics: from GaN substrate to Intelligent Energy Bank".