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

Abstract

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 Ga or Si Ga . This contact shows exceptionally smooth surface morphology, as revealed by atomic force microscopy (AFM).

Low resistance copper-based ohmic contact for AlGaN/GaN high electron mobility transistors

“…The fact that a good ohmic behavior was obtained implied that Cu was completed consumed and no trace was left to contact with or diffuse into the semiconductor. 15 This is consistent with the Auger result that the Cu signal was stopped at Ti layer. Nevertheless, further study of the reliability of Cu-based ohmic contacts is needed for future device applications.…”

“…[11][12][13] An effective diffusion barrier to Cu is thus required, especially for the ohmic contact. A few ohmic contact structures for GaN devices, such as Si/Ti/Al/Cu/Au, 14 Ge/Cu/Ge, 15 and Ti/Cu/Ge, 16 have been investigated. Although ohmic contacts could be achieved at relatively lower temperatures (<800 C) for these structures, they all suffer from having high contact resistance (r c > Â 10 -5 ohm cm 2 ).…”

Ti/Al/Ni/Cu Ohmic Contact with Low Contact Resistance and Smooth Surface Morphology for AlGaN/GaN HEMT

“…Researchers were looking into ways of making ohmic contact with lower annealing temperatures. Ohmic structures such as Si/Ti/Al/Cu/Au 18 , Ge/Cu/Ge 19 and Ti/Cu/Ge 20 have been successfully formed at lower temperature (< 800 °C). However, these structure were all having relatively high contact resistance (r c > 10 -5 Ω-cm) and thus limited their usefulness.…”