Effect of graphite related interfacial microstructure created by high temperature annealing on the contact properties of Ni/Ti/6H-SiC

Abstract

• Ni (120 nm)/Ti (20 nm) Ohmic contacts to 6H-SiC were prepared by annealing method. • A minimum specific contact resistance of 5.9 × 10 −5 Ω cm 2 was obtained at 950 °C. • An obvious increase in the degree of graphitization process was observed. • C dangling bond at the interface is crucial in obtaining good Ohmic contact. • The graphite related interfacial structure favors the formation of C dangling bond. Ni/Ti bilayer contacts were prepared on n-type 6H-SiC, and the formation mechanism of Ohmic contact was discussed. The electrical properties and microstructure of the Ni/Ti contacts were analyzed by transmission line model method, Raman spectroscopy, glancing angle X-ray diffraction and transmission electron microscopy. The Ni/Ti contacts show Schottky behavior when the annealing temperature is below 950 °C, while they exhibit Ohmic behavior with a very low specific contact resistance of 5.90 × 10 −5 Ω cm 2 when annealed above 950 °C. An obvious increase trend in the degree of graphitization process is observed in Raman spectra with increasing the annealing temperature. TEM results show a typically interfacial microstructure with a large area of high quality graphite uniformly dispersed at the rough interface and directly contacted with SiC above 950 °C. This typically interfacial microstructure improved the Ohmic contact properties through forming the large area and high quality C dangling bonds at the surface of SiC substrate, which decrease the Schottky barrier height at the interface by lowering the surface state density of SiC substrate after annealing.