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-O_x 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-O_x metallization structure. For this purpose, a Ni-Mg-O_x 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-O_x 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-O_x 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-O_x 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-O_x p-GaN structure in comparison with the Au/Ni-O_x 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

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