Achieving ≥ 1200-V High-Performance GaN HEMTs on Sapphire With Carbon-Doped Buffer

GaN-on-sapphire has recently attracted great attention for power electronics. Although plenty of efforts have already been made in this topic decades ago, but thorough evaluation on the buffer for $\ge 1200$ -V devices are, however, lacking. In this work, two promising buffers, i.e., AlGaN buffer and carbon-doped GaN buffer (C:GaN), are compared. The key results demonstrate that by replacing the AlGaN buffer with C:GaN buffer, the full-widths at half-maximums (FWHMs) of $\omega $ -rocking curves for (002) and (102) planes reduce from 785 and 2421 to 488 and 1240 arcsec, respectively, and the average sheet resistance ${R}_{\Box }$ drops from 501 to $342~\Omega $ / $\Box $ and its nonuniformity improves from 4.6% to 1.9%. The fabricated high-electron-mobility transistors (HEMTs) exhibit an optimized ${R}_{\text {ON}}$ from 22.1 to $16.1~\Omega \cdot $ mm, a more uniform off-state blocking capability, and an improved dynamic ${R}_{\text {ON}}$ degradation from 104% to 50.4%. Capacitance and conductance analysis discovered that an extra group of deep traps is introduced by the AlGaN buffer. Further photoluminescence (PL) spectroscopy unveils a stronger yellow luminescence (YL), corresponding to a higher density of radiation-related defect recombination centers induced by the AlGaN buffer. Overall, this work unambiguously shows the carbon dopants, often used in GaN-on-Si epitaxy, can help to facilitate the commercialization of $\ge 1200$ -V HEMTs on sapphire in the future.