Combinatorial investigation of structural quality of Au/Ni contacts on GaN

A combinatorial library of Au/Ni metallizations on GaN was microstructurally characterized by X-ray diffraction (XRD), electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM). The array of single- and bi-layered metal elements of systematically varying thicknesses was deposited by electron-beam evaporation on a GaN/c-sapphire wafer. The elements with a single layer of Au on GaN had a fiber texture with h1 1 1i preferred growth orientation. TEM revealed a 2 nm thick amorphous contamination layer between the Au and GaN, which prevented the gold from being epitaxial. By contrast, nickel in both the single-layered Ni and bi-layered Au/Ni elements formed epitaxially on the GaN with a (1 1 1)fcc// (0 0 0 1)hex, h1 10ifcc==h11 20ihex orientation relation, as observed by TEM and EBSD. The Ni layer formed two types of domains related by a 608 rotation about h1 1 1ifcc, which were replicated by the Au over-layer in the Au/Ni structures. The improved structural quality of the bi-layered Au/Ni as compared to the single-layered Au was due to the removal of native contamination from the GaN surface during the initial step of Ni deposition; this promoted epitaxial growth of both metal layers. However, as the nickel interlayer thickness was increased above 5 nm, the Au/Ni structural quality decreased, as measured by increased deviations from the (1 1 1)fcc//(0 0 0 1)hex orientation relation. # 2003 Elsevier B.V. All rights reserved.