Activating Thick Buried p-GaN for Device Applications

Many emerging GaN electronic and optoelectronic devices comprise p-GaN layers buried below n-GaN or AlGaN. The activation of these buried p-GaN layers usually relies on the lateral hydrogen diffusion through the etched mesa sidewalls, which is known to induce nonuniform acceptor distributions. However, the acceptor profile, electric field (
${E}$
-field) blocking capability, and leakage current mechanisms of the sidewall activated p-GaN layer have not been fully understood. This work addresses these knowledge gaps by fabricating vertical GaN p-n diodes with a thick (
$3.8~\mu \text{m}$
) p-GaN. Two activation schemes were performed to allow the hydrogen diffusion through sidewalls and the top surface. For the sidewall activation, an analytical model was developed to depict the spatial distribution of the activated acceptor and the temporal evolution of this distribution with the increased annealing time. This model was validated using the
${C}$
–
${V}$
characteristics of the fabricated diodes with various radii. Under reverse biases, the breakdown
${E}$
-field and leakage current of the sidewall-activated diodes were found to be determined only by the edge area with the highest activation efficiency. The leakage mechanism agrees with the trap-assisted tunneling (TAT) model, and the peak junction
${E}$
-field can exceed 3 MV/cm, both being similar to those of surface-activated diodes. These results provide critical information for the design and processing of advanced GaN devices with the buried p-GaN.