Critical electric fields of AlGaN in AlGaN-based vertical conducting diodes on nn-SiC substrates

We have succeeded in obtaining high critical electric fields from AlGaN layers using the p-InGaN/i-AlxGa1−xN/n-AlxGa1−xN (x=0–0.22x=0–0.22) vertical conducting diodes grown on nn-SiC substrates by low-pressure metalorganic vapor phase epitaxy (MOVPE). The breakdown voltage (VBVB) increases with increasing Al composition of the AlGaN layer. The corresponding critical electric fields are calculated to be 2.4 MV/cm for GaN and 3.5 MV/cm for Al0.22Ga0.78N. The critical electric field is proportional to the bandgap energy to a power of 2.5. This bandgap energy dependence is much stronger than that in the empirical expression proposed by Sze and Gibbons. The figure of merit, (VB)2/Ron, increases with increasing Al composition, indicating the AlGaN-based p–i–np–i–n diodes are promising for high-power and high-temperature electronic device applications.