Abstract
The thermal stability of the Ti/Al, Ti/Al/Ni/Au, Cr/Al and Cr/Al/Ni/Au ohmic contact metallizations on n-GaN were investigated. Bilayers of Ti/Al and Cr/Al, with and without Ni/Au overlayers, were deposited on n-GaN using an e-beam deposition method and ohmic contacts formed by a vacuum annealing technique. For both the Ti/Al and Ti/Al/Ni/Au minimum specific contact resistivities of ∼ 1×10 −5 Ω cm 2 were achieved after vacuum annealing at 1100 °C for 2 min. Minimum specific resistivities of similarly formed Cr/Al and Cr/Al/Ni/Au ohmic contacts were 3.8×10 −5 and 2.3×10 −5 Ω cm 2 respectively, obtained at 700 and 950 °C respectively. The above mentioned contacts were exposed to long term aging at temperatures of 300, 400 and 500 °C, for periods up to 100 h and their electrical and morphological characteristics were monitored at the various stages of the aging process. The Ti/Al and Cr/Al/Ni/Au proved to be the most stable of the four metallizations in terms of both electrical performance and surface morphology. The Cr/Al had shown stable morphological stability, but displayed the poorest electrical performance characteristics as a result of the aging process.
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