Low on-resistance of GaN p-i-n vertical conducting diodes grown on 4H-SiC substrates

We investigated the resistance of conductive AlGaN buffer layers and the current-voltage characteristics of GaN p-i-n vertical conducting diodes on n-type 4H-SiC substrates grown by low-pressure metalorganic vapor-phase epitaxy. High Si doping of the AlGaN buffer layer at the AlGaN/SiC interface produces ohmic current-voltage characteristics in spite of the large band offset between AlGaN and 4H-SiC. Owing to the optimization of the AlGaN buffer layer, a low on-resistance (R_on) of 1.12 mΩ cm² with high breakdown voltage (V_B) of 300 V is obtained for a GaN p-i-n vertical conducting diode on a 4H-SiC substrate, leading to the figure of merit (V _B2/R_on) of 80 MW/cm², which is larger than that for the diode with the same structure on a 6H-SiC substrate (62 MW/cm2). This result indicates that 4H-SiC is preferable for fabricating GaN-based electronic devices with a low on-resistance and high breakdown voltage.