Compositional Study of Copper-Germanium Ohmic Contact to n-GaN

400°C alloying of Ge/Cu/Ge films on modestly doped n-GaN results in linear current-voltage (I-V) behavior over a wide range of relative Ge compositions. X-ray diffraction (XRD) and Auger depth profiling data suggest that the lowest contact resistivity is due to film compositions near 25 at.% Ge, where the amount of interfacial nonreacted Ge is low. Ohmic contact is likely established by a heavily doped GaN interfacial region influenced by premetallization reactive ion etching (RIE) and later low-temperature alloying, which assists in the formation of donorlike complexes possibly involving Ge^sub Ga^ or Si^sub Ga^. This contact shows exceptionally smooth surface morphology, as revealed by atomic force microscopy (AFM). [PUBLICATION ABSTRACT]