Design and fabrication of Schottky barrier diodes on SiC

Schottky diodes with blocking voltages in excess of 1 kV have been demonstrated on 4H-and 6H-SiC. The metal field plate structure has been utilized for reducing electric field crowding at the periphery of the diodes. These diodes have been shown to have a lower on-resistance (4.4 m{dollar}Omega{dollar}Z-cm{dollar}sp2{dollar}) than conventional Si p-i-n or Schottky diodes of similar breakdown voltage ratings due to the thinner and more heavily-doped drift layer. It is possible to have such thinner and more heavily doped drift layer in SiC (compared to Si) for similar breakdown voltage ratings by virtue of the high breakdown electric field ({dollar}sim{dollar}10x compared to Si) of SiC. The lower on-resistance of the diodes in turn results in lower forward voltage drop at high operating current densities (e.g. 1.6-1.8 V at 100 A/cm{dollar}sp2{dollar}). In addition, the refractive metals such as Ni and Pt utilized for Schottky contacts to SiC in this study have resulted in large barrier heights ({dollar}>{dollar}1.1 eV). The large barrier height reduces the leakage currents in the Schottky diodes (less than 10{dollar}sp{lcub}-2{rcub}{dollar} A/cm{dollar}sp2{dollar} at {dollar}-{dollar}1000 V for Ni/4H-SiC diodes). Current ON/OFF ratios (ratio of the forward current density at 2 V to the reverse current density at {dollar}-{dollar}500 V) in excess of 10{dollar}sp7{dollar} has been obtained for Ni/4H-SiC diodes at room temperature. The diodes have been found to retain excellent rectifying behavior at high temperatures, with only a slight degradation in the ON/OFF ratios resulting from the increase in leakage currents. ON/OFF:ratios in excess of 10{dollar}sp6{dollar} have been measured up to temperatures of 300{dollar}spcirc{dollar}C. The effect of area of circular Ni/4H-SiC diodes on the resulting current-voltage characteristics has been studied and leakage currents have been measured as a function of the diode Area-to-Perimeter ratio. A strong decreasing effect in the leakage current density has been observed for the diodes as the diode diameter is increased from 30{dollar}mu{dollar}m to 200{dollar}mu{dollar}m. The rectifier efficiency (rectification ratio) of the diodes has been studied at varying frequencies of the applied a.c. voltage and at high temperatures up to 300{dollar}spcirc{dollar}C. A rectification ratio close to the ideal expected value has been observed for frequencies up to 600 kHz and temperatures up to 300{dollar}spcirc{dollar}C. These results of the study show that high voltage Schottky diodes on SiC diodes have good prospects for several high power applications.