Activation of buried p-GaN in MOCVD-regrown vertical structures

Abstract

Thermal activation of buried p-type GaN is investigated in metal-organic chemical vapor deposition-regrown vertical structures, where the buried p-GaN is re-passivated by hydrogen during regrowth. The activation is performed by exposing the buried p-GaN through etched sidewalls and characterized by reverse breakdown measurements on vertical diodes. The effect of the n-type doping level on the activation has been observed. After 725 °C/30 min annealing in a dry air environment, the buried p-GaN with a regrown unintentionally-doped (UID) capping layer is sufficiently activated due to significant Mg-incorporation in the UID layer, allowing for hydrogen up-diffusion. With an additional regrown n+-GaN capping layer (i.e., in n+/i/p-n diodes), only lateral diffusion of H out of the exposed mesa sidewall is permitted. A critical lateral dimension between 10 and 20 μm is found for the n+/i/p-n diodes, under which the buried p-GaN is sufficiently activated. The diodes with activated buried p-GaN achieved up to 1200 V breakdown voltage, indicating that over 28% of the Mg dopants is activated. The study demonstrates the effectiveness of sidewall p-GaN activation in achieving high breakdown voltage pertinent to GaN vertical power devices, while providing guidelines on the required device geometry.