Dependence of the Au/Ni/Si/Ni Contact Properties on the Si-layer Thickness and the Annealing Temperature in p -type GaN
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T.W. Kim Department of Physics, Kwangwoon University, 447-1 Wolgye-dong, Nowon-ku, Seoul 139-701, Korea
K.S. Chung Department of Electronic Engineering, Kyung Hee University, Seocheon-Ri, Kilheung-Eup, Yongin-City, Kyungki-do, Korea (Received 18 July 2001; accepted 7 February 2002)
The dependences of the properties of Au/Ni/Si/Ni contacts, deposited on p-GaN epilayers by using electron-beam evaporation, on the Si layer thickness and the annealing temperature were investigated with the goal of producing contacts with low specific resistances. The results of the current–voltage (I–V ) curves showed that the lowest specific contact resistance obtained for the Au/Ni/Si/Ni contact with a 1200-Åthick Si layer on p-type GaN annealed at 700 °C for 1 min in a nitrogen atmosphere was 8.49 × 10−4 ⍀ cm2. The x-ray diffraction (XRD) measurements on the annealed Au/Ni/Si/Ni/p-GaN/sapphire heterostructure showed that Ni3Si, GaAu, and NiGa layers were formed at the Au/Ni/Si/Ni/p-GaN interfaces. While the intensities corresponding to the Ni3Si layer decreased with increasing annealing temperature above 700 °C, those related to the GaAu and the NiGa layers increased with increasing temperature. These results indicate that the Au/Ni/Si/Ni contacts with 1200-Å-thick Si layers annealed at 700 °C hold promise for potential applications in p-GaN-based optoelectronic devices.
I. INTRODUCTION
Recently, the successful achievement of a p-type GaN epilayer with high quality has driven particular interest in their applications to optoelectronic devices operating from the visible to the ultraviolet spectral regions at room temperature.1–5 Stable contacts on the epilayers are very important for the fabrication of devices utilizing p-GaN epitaxial layers.6 Specific contact resistances of at least as small as approximately 1 ⍀ mm2 are necessary to improve device efficiency.7 Even though some works concerning the contact properties of metal/n-GaN epilayers have been carried out,8–16 by comparison, relatively little study has been performed on the contact problems of metal/p-GaN epilayers. 17–22 Despite the technical achievement of a useful contact on a metal/p-GaN epilayer, more studies of the formation of stable contacts on p-GaN epilayers are needed to achieve long-lifetime operation of GaN-based light-emitting diodes and lasers.20 Furthermore, because thermal treatment is necessary for the fabrication processes of several kinds of optoeleca)
Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 17, No. 5, May 2002
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tronic devices, the role of the thermal annealing processes is very important in achieving high-performance devices.23 Therefore, studies of the annealing effects on contact properties play a very important role in enhancing device efficiency. This paper reports on the dependences of the properties of Au/Ni/Si/Ni contacts on the Si-layer thickness and on the annealing temperature for Mg-doped p-type GaN epilayers grown on sapphire
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