Vertical GaN p-n Junction Diodes With High Breakdown Voltages Over 4 kV

Vertical structured GaN power devices have recently been attracting a great interest because of their potential on extremely high-power conversion efficiency. This letter describes increased breakdown voltages in the vertical GaN p-n diodes fabricated on the free-standing GaN substrates. By applying multiple lightly Si doped n-GaN drift layers to the p-n diode, the record breakdown voltages (V_B) of 4.7 kV combined with low specific differential ON-resistance (R_ON) of 1.7 mΩcm² were achieved. With reducing the Si-doping concentration of the top n-GaN drift layer adjacent to the p-n junction using well-controlled metal-organic vapor phase epitaxy systems, the peak electric field at the p-n junction could be suppressed under high negatively biased conditions. The second drift layer with a moderate doping concentration contributed to the low R_ON. A Baliga´s figure of merit (V_B²/R_ON) was 13 GW/cm². These are the best values ever reported among those achieved by GaN p-n junction diodes on the free-standing GaN substrates.