Excellent wet etching technique using pulsed anodic oxidation for homoepitaxially grown GaN layer

In vertical devices containing GaN homoepitaxial layers on free-standing GaN substrates, damageless trench fabrication is a key issue in device processes. We used a free-standing GaN substrate with a dislocation density of 10 6 cm −2 and applied pulsed photo-electrochemical (PEC) etching to a homoepitaxially grown n − -GaN layer. Although the reported results of GaN-on-sapphire show poor etching uniformity caused by the high dislocation density in the range of 10 8 to 10 9 cm −2 , the etched surface of GaN-on-GaN obtained by pulsed PEC etching was almost flat at a low etching voltage. The photoluminescence intensity indicated that the etched surface does not have etching damage. Furthermore, we successfully obtained wet-etched mesa diodes with a high breakdown voltage of more than 3 kV and a high yield. These results indicate the applicability of pulsed PEC etching to the damageless trench fabrication of vertical GaN power devices using low-dislocation-density GaN substrates.