Analysis of the inhomogeneous barrier and phase composition of W/4H-SiC Schottky contacts formed at different annealing temperatures

The electrical characteristics of W/4H-SiC Schottky contacts formed at different annealing temperatures have been measured by using current-voltage-temperatures (I-V-T) and capacitance-voltage-temperatures (C-V-T) techniques in the temperature range of 25 ℃-175 ℃. The testing temperature dependence of the barrier height (BH) and ideality factor (n) indicates the presence of inhomogeneous barrier. Tung's model has been applied to evaluate the degree of inhomogeneity, and it is found that the 400 ℃ annealed sample has the lowest T₀ of 44.6 K among all the Schottky contacts. The barrier height obtained from C-V-T measurement is independent of the testing temperature, which suggests a uniform BH. The x-ray diffraction (XRD) analysis shows that there are two kinds of space groups of W when it is deposited or annealed at lower temperature (≤ 500 ℃). The phase of W₂C appears in the sample annealed at 600 ℃, which results in the low BH and the high T₀. The 500 ℃ annealed sample has the highest BH at all testing temperatures, indicating an optimal annealing temperature for the W/4H-SiC Schottky rectifier for high-temperature application.