Electrical evolution of W and WC Schottky contacts on 4H-SiC at different annealing temperatures

In this paper, we investigate the electrical evolution of tungsten (W) and tungsten carbide (WC) Schottky contacts on 4H-SiC subjected to thermal treatments at different annealing temperatures from 475 C to 700 C. For each annealing temperature, the uniformity of the Schottky barrier height (ΦB) and ideality factor (n) was monitored by current-voltage (I-V) measurements in forward bias, performed over sets of equivalent diodes. Good values of n (below 1.05) were found for both contacts up to thermal annealing at 700 C. On the other hand, the barrier of the two contacts behaves differently. For the W/4H-SiC diode, the ΦB increases with the annealing temperature (from 1.14 eV at 475 C to 1.25 eV at 700 C), whereas the Schottky barrier in WC/4H-SiC features a slight reduction already with thermal annealing at 475 C, remaining almost constant at around 1.06 eV up to annealing at 700 C. A deeper characterization was performed on the 700 C-annealed contacts by studying the temperature-dependence of the Schottky parameters by current-voltage-temperature (I-V-T) characterization. The ΦB and n behaviour with temperature indicates the presence of a nanoscale lateral inhomogeneity for both Schottky contacts, which can be described by Tung's model. Finally, the temperature-dependence of the reverse characteristics could be described by the thermionic field emission model, accounting for the temperature dependent barrier height determined from forward characterization.