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

TL;DR

This study examines how tungsten and tungsten carbide Schottky contacts on 4H-SiC change electrically after thermal treatments at various temperatures, revealing differences in barrier height evolution and nanoscale inhomogeneities.

Contribution

It provides new insights into the thermal stability and electrical behavior of W and WC Schottky contacts on 4H-SiC, including detailed temperature-dependent analysis.

Findings

W/4H-SiC barrier height increases with annealing temperature

WC/4H-SiC barrier height remains nearly constant after annealing

Both contacts exhibit nanoscale inhomogeneities explained by Tung's model

Abstract

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 to 700 {\deg} C. For each annealing temperature, the uniformity of the Schottky barrier height (${\phi_B}$) 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 {\deg} C. On the other hand, the barrier of the two contacts behaves differently. For the W/4H-SiC diode, the ${\phi_B}$ increases with the annealing temperature (from 1.14 eV at 475 {\deg} C to 1.25 eV at 700 {\deg} C), whereas the Schottky barrier in WC/4H-SiC features a slight reduction already with thermal annealing at 475 {\deg} C, remaining almost constant at around 1.06 eV up to annealing at 700 {\deg} C. A deeper characterization was performed on the 700 {\deg} C-annealed contacts by studying the temperature-dependence of the Schottky parameters by current-voltage-temperature (I-V-T) characterization. The ${\phi_B}$ 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 (TFE), accounting for the temperature dependent barrier height determined from forward characterization.