INVESTIGATION OF LOW-RESISTANCE AND HIGH-RESISTANCE NI-GE-AN OHMIC CONTACTS TO N(+) GAAS USING ELECTRON MICROBEAM AND SURFACE ANALYTICAL TECHNIQUES

A process for the formation of low-resistance Ni-Ge-Au ohmic contacts to n(+) GaAs has been refined using multivariable screening and respon se surface experiments. Samples from the refined, low-resistance proce ss (which measure 0.05 +/- 0.02 Omega . mm) and the unrefined, higher resistance process (0.17 +/- 0.02 Omega . mm) were characterized using analytical electron microscopy (AEM), transmission electron microscop y (TEM), scanning electron microscopy-energy dispersive spectroscopy ( SEM-EDS), and x-ray photoemission spectroscopy (XPS) depth profiling m ethods. This approach was used to identify microstructural differences and compare them with electrical resistance measurements, Analytical results of the unrefined ohmic process sample reveal a heterogeneous, multiphase microstructure with a rough alloy-GaAs interface, The sampl e from the refined ohmic process exhibits an alloy which is homogeneou s, smooth, and has a fine-grained microstructure with two uniformly di stributed phases. XPS analysis for the refined ohmic process sample in dicates that the Ge content is relatively depleted in the alloy (relat ive to the deposited Ge amount) and enriched in the GaAs, This is not evidenced in the unrefined ohmic process sample, Our data lead us to c onclude that a smooth, uniform, two-phase microstructure, coupled with a shift in Ge content from the post-alloy metal to the GaAs, is impor tant in forming low-resistance ohmic contacts.