I understand that a GAN body diode is still there? So do I need a parallel external diode for reverse diode protection?
GaN does not have a body diode, which means GaN doe snot have any reverse recovery (QRR), but GaN can work in reverse conduction. When VGS or VGD voltage is above threshold voltage(Vgsth), the FET will conduct. When the GaN FET operates in reverse conduction condition, the VSD needs to be above VGS(th) which is higher than tpyical MOSFET body diode forward voltage. This may cause higher loss if the timing of reverse conduction condition is long, so paralleling a diode at the low side GaN FET can reduce this loss. We usually recommend a Schottky diode to parallel with the GaN FET since Schottky diode has lower forward voltage. For more information on optimizing deadtime please view the webinar Understanding the Impact of Dead-time, QRR, and COSS