High-transparency Ni/Au bilayer contacts to n-type GaN

Abstract

A unique metallization scheme has been developed for obtaining both Schottky and low-resistance Ohmic contacts to n-GaN. It has been demonstrated that the same metallization can be used to make both Schottky and Ohmic contacts to n-GaN using a Ni/Au bilayer composite with Ni in contact to GaN. Using this metallization, contacts with a specific contact resistivity, ρs, as low as 6.9×10−6 Ω cm2 for a doping level of 5.0×1017 cm−3 was obtained after annealing the sample for 10 s at 800 °C in a rapid thermal annealer. The presence of only (111)Au and (111)Ni peaks in the x-ray diffraction (XRD) pattern of as-deposited samples indicates that both metals participate to form epitaxial or highly textured layers on the basal GaN plane. When the contact layer is annealed, Au and Ni react with GaN creating interfacial phases. Both XRD and transmission electron microscopy confirm that Ni3Ga and Ni2Ga3 intermetallic phases together with Au and Ni based face-centered-cubic solid solutions, are formed during annealing. The high optical transmission achieved (in the range of 400–700 nm) through this contact after annealing suggests that it is, indeed, very useful for electro-optic device applications. The contacts also demonstrate exceptional thermal stability. Experimental data suggest that the formation of interfacial phases with a low work function is responsible for the low contact resistance of the system. The Ni–Au layer forms a robust composite enabling the contacts to have high-temperature applications. Unlike the Ni/Au Ohmic contact, the Ni/Au Schottky contact to n-GaN has a relatively large barrier height. Improved material quality and Schottky contact technology are needed to improve upon the reverse breakdown voltage.

Contact mechanisms and design principles for Schottky contacts to group-III nitrides

“…As evident from our energy dispersive x ray/electron-energy-loss spectroscopy ͑EDX/ EELS͒ plot ͑Fig. 2͒ for Au/ Ni/ Ti/ n-GaN contact annealed at 800°C, and from earlier investigations, 10,13 Au and Ni are highly diffusive, Au is more diffusive than Ni, and Ta is marginally diffusive, at about 700°C ഛ T RTA ഛ 800°C. So, if the Ni/ Ta/ n-GaN or Au/ Ta/ n-GaN contacts are formed with L 1 ϵ Ta and L 2 ϵ Ni or Au, and then these contacts are annealed at 700-800°C, L 2 ϵ Ni or Au will diffuse rapidly through Ta onto the n-GaN surface.…”

“…It shows how M-S interaction can be carefully tailored to lower the M-S energy until the latter reaches E MS0 . With input from previous studies, 5,10 it highlights the very superiority of the two-step surface preparation technique.…”

“…[3][4][5][6][7][8][9][10][11][12][13][14][15][16] Our objective in this investigation is to extend this effort and to focus attention to exploring unified design rules and contact mechanisms for the design and characteristics of the metal/nitride Schottky contacts. One central theme of the study is to identify the fundamentals that distinguish Schottky contacts from ohmic contacts.…”

Sintered Cr/Pt and Ni/Au ohmic contacts to B12P2

“…This may be caused by Ni diffusion and segregation at the sample surface, which is common for Ni/Au contacts on other materials such as GaN. [34][35][36][37] To further investigate the interfaces in the Au/Ni/B 12 P 2 system, RBS was performed on a sample before any heat treatment and after the 500 C anneal, which caused a major change in the I-V characteristics. The RBS spectra are shown in Fig.…”

High throughput characterization of the optical properties of compositionally graded combinatorial films

“…More recently, the tool was used for high throughput optical measurements of a Au/Ni combinatorial library film on n-GaN/sapphire. GaN is of interest for optoelectronic devices such as light emitting diodes and laser diodes [5], and the Au/Ni(O) system is a candidate transparent electrode [6,7] material for nitride-based devices.…”