Thermal annealing effects on the electrical and structural properties of Mo Schottky contacts to n-type 4H-SiC

In this work, the effects of high-temperature (700, 950 °C) annealing on the electrical and structural properties of Mo/4H-SiC Schottky contacts were studied. The ideality factor and Schottky barrier height were evaluated by means of current-voltage measurements, observing a reduction of the barrier height from 1.45 eV in the as-deposited contact down to 1.29 eV in the 950 °C-annealed contact. The degree of barrier inhomogeneity was evaluated by the temperature dependence of the current-voltage characteristics of the Mo/4H-SiC contacts. Furthermore, annealed contacts showed a positive effect of the thermal annealing in reducing the NSS level in the region closest to the bottom of the conduction band. The electrical behavior was correlated with structural analyses of the interface, which did not show any reaction of the metal layer with the 4H-SiC surface, even at the highest annealing temperature. However, a re-arrangement of the Mo-film structure, with an enlargement of the grains and their preferential orientation towards the [110] direction was observed upon annealing at 950 °C. These structural changes can be responsible for the reduction of the Schottky barrier height of the Mo/4H-SiC contact observed during annealing.