Study of Ti/Al/Ni ohmic contacts to P-type implanted 4H-SiC

This work reports on the electrical and microstructural properties of Ti/Al/Ni contacts to p-type implanted 4H-SiC obtained by rapid thermal annealing of a metal stack of Ti(70 nm)/ Al(200 nm)/Ni(50 nm). The contact characteristics were monitored at increasing value of the annealing temperature. The Ohmic behavior of the contact, with a specific contact resistance value of 2.3×10 ?·cm, is obtained for an annealing at 950 °C. The structural analyses of the contact, carried out by XRD and TEM, reveal the occurrence of reactions, with the detection of the AlNi and AlTi phases in the upper part of the contact and of an epitaxially oriented TiC layer at the interface. These reactions are considered the key factors in the formation of an Ohmic contact in our annealed Ti/Al/Ni system. The temperature-dependence study of the electrical characteristics reveals a predominant thermionic field emission (TFE) mechanism for the current conduction through the contact, with a barrier height of 0.56 eV.