OHMIC CONTACTS TO p-GaN USING Au/Ni-Mg-O METALLIZATION
Jozef Liday – Peter Vogrinčič – Ivan Hotový – Vlastimil Řeháček – Juraj Breza – Alberta Bonanni – Helmut Sitter – Tibor Lalinský – Gabriel Vanko
Electrical characteristics and elemental depth profiles of ohmic contacts to p-GaN using Au/Ni-Mg-Ox metallization have been investigated. The
objective was to examine the possibilities of increasing the charge carrier concentration in the surface region of GaN by adding Mg, thus of a p-type
dopant into the Au/Ni-Mg-Ox metallization structure. For this purpose, a Ni-Mg-Ox layer with a low concentration of Mg was deposited on
p-GaN by dc reactive magnetron sputtering.
The top Au layer was deposited in a similar way. The fabricated contact structures were annealed in
N2$. When the Ni-Mg layer in the Au/Ni-Mg-Ox p-GaN structure was deposited in an atmosphere with a low concentration of oxygen
(0.2\,at %), the structure exhibited a low resistance ohmic nature. The contact resistance was lower than in the case of a Au/Ni-Ox p-GaN
structure without the Mg dopant in the metallic layer. An increase in the concentration of oxygen in the working atmosphere resulted in higher values
of the contact resistance of the Au/Ni-Mg-Ox p-GaN structure. In our opinion the ohmic nature of the contact structure is related to the
existence of a metal/p-NiO/p-GaN scheme. The measured values of the contact resistance in the Au/Ni-Mg-Ox p-GaN structure in comparison
with the Au/Ni-Ox p-GaN structure are caused by an increased charge carrier concentration in the surface region of p-GaN, which is a
consequence of Mg diffusion from the Ni-Mg-O layer.
Keywords: rubrene, p-GaN, Au/Ni-Mg-O/p-GaN contact structure, AES depth profiling, low resistance