The influence of thermal annealing on the characteristics of Au/Ni Schottky contacts on n-type 4H-SiC

The effects of isochronal annealing on the electrical, morphological and structural characteristics of Au/Ni/4H-SiC Schottky barrier diodes (SBDs) have been studied. Current-voltage (I-V), capacitance-voltage (C-V), deep-level transient spectroscopy, scanning electron microscope (SEM) and X-ray diffraction measurements were employed to study the thermal effect on the characteristics of the SBDs. Prior to thermal annealing of Schottky contacts, the I-V measurements results confirmed the good rectification behaviour with ideality factor of 1.06, Schottky barrier height of 1.20 eV and series resistance of 7 Omega. The rectification properties after annealing was maintained up to an annealing temperature of 500 degrees C, but deviated slightly above 500 degrees C. The uncompensated ionized donor concentration decreased with annealing temperature, which could be attributed to out-diffusion of the 4H-SiC into the Au/Ni contacts and decrease in bonding due to formation of nickel silicides. We observed the presence of four deep-level defects with energies 0.09, 0.11, 0.16 and 0.65 eV below the conduction band before and after the isochronal annealing up to 600 degrees C. The conclusion drawn was that annealing did not affect the number of deep-level defects present in Au/Ni/4H-SiC contacts. The variations in electrical properties of the devices were attributed to the phase transformations and interfacial reactions that occurred after isochronal annealing.