Improved Ni ohmic contact on n-type 4H-SiC

This paper presents the structural, chemical and electronic properties of Al/Ni/Al-layers evaporated on 4H silicon carbide and then annealed at 1000 degrees C for 5 min. The structure was investigated before and after annealing by transmission electron spectroscopy from cross-sectional specimens. With x-ray photoelectron spectroscopy, both element distribution and bonding energies were followed during sputtering through the alloyed metal-semiconductor contact. Voids are found in both annealed Ni/4H-SiC and Al/Ni/Al/4H-SiC contact layers, though closer to the metal-semiconductor interface in the former case. The first aluminum-layer is believed to prevent voids to be formed at the interface and also to reduce the oxide on the semiconductor surface. The contact was found to be ohmic with aspecific contact resistance rho(c) = 1.8 x 10(-5) Omega cm(2) which is more than three times lower rho(c) than for the ordinary Ni/4H-SiC contact prepared in the same way.