A chemical and structural investigation of Schottky and ohmic Au/GaAs contacts

Abstract

Recently we have shown that the gold contacts deposited on ultrahigh vacuum cleaved (110) n-GaAs exhibit strongly rectifying Schottky barrier-type behavior which becomes ‘‘ohmic’’ upon annealing due to a nonrectifying low-resistance current pathway at the periphery of the contact. These Au/n-GaAs contacts are of particular interest because of this rectifying to ohmic transition. Using scanning Auger electron spectroscopy (AES), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques combined with electrical device measurements, we are able to correlate the change in ohmic behavior for diodes annealed in a nitrogen environment above 360 °C with the formation of very thin, long, predominantly Au crystallites on the surface of the GaAs at the periphery of the contact. These crystallites are typically 5–10 μ long, 500–2000 Å wide, and are crystallographically oriented along the GaAs 〈110〉 direction. TEM and AES sputter profiles have shown that these structures are ∼100–150 Å thick. Glancing incidence sputtering using 1-keV Ar ions with sample rotation, as well as a wet chemical mesa etch (H2SO4:H2O2:H2O), were used to selectively remove the crystallites from around the periphery. AES, SEM, and TEM confirm the removal of the crystallites. After this removal, the rectifying behavior of the diode was restored. This demonstrates that the presence of the thin Au crystallites can be correlated with the ohmic behavior in this system.