High critical electric field of AlxGa1−xN p-i-n vertical conducting diodes on n-SiC substrates

We report the current-voltage characteristics of ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{N}$ $(x=0–0.22)$ $p\text{-}i\text{-}n$ vertical conducting diodes grown on $n\text{-}\mathrm{Si}\mathrm{C}$ 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 $2.4\mathrm{MV}∕\mathrm{cm}$ for GaN and $3.5\mathrm{MV}∕\mathrm{cm}$ for ${\mathrm{Al}}_{0.22}{\mathrm{Ga}}_{0.78}\mathrm{N}$ . 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 $5.2\mathrm{V}$ even in the case of the ${\mathrm{Al}}_{0.22}{\mathrm{Ga}}_{0.78}\mathrm{N}$ $p\text{-}i\text{-}n$ diode.