High critical electric field of Al_xGa_1-xN p-i-n vertical conducting diodes on n-SiC substrates

We report the current-voltage characteristics of Al_xGa _1-xN (x=0-0.22) p-i-n vertical conducting diodes grown on n-SiC substrates by low-pressure metal organic vapor phase epitaxy. An increase in the breakdown voltage was experimentally demonstrated with increasing Al composition. The corresponding critical electric fields were calculated to be 2.4 MVcm for GaN and 3.5 MVcm for Al0.22 Ga0.78 N. The critical electric field is proportional to the band gap energy to a power of 2.5. The forward voltage drop also increases with increasing Al composition but it is still as low as 5.2 V even in the case of the Al0.22 Ga0.78 N p-i-n diode.