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

We have succeeded in obtaining high critical electric fields from AlGaN layers using the p-InGaN/i-Al_xGa_1-xN/n-Al_xGa_1-xN (x = 0 - 0.22) vertical conducting diodes grown on n-SiC substrates by low-pressure metalorganic vapor phase epitaxy (MOVPE). The breakdown voltage (V_B) 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 Al_0.22Ga_0.78N. 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, (V_B)² / R_on, increases with increasing Al composition, indicating the AlGaN-based p - i - n diodes are promising for high-power and high-temperature electronic device applications.