Improved Vertical Isolation for Normally-Off High Voltage GaN-HFETs on n-SiC Substrates

Argon implantation of n-type SiC substrates prior to epitaxial growth of AlGaN/GaN HFETs stacks is used to decrease the vertical leakage to the conductive substrate. Normally-off p-GaN gate transistors with AlGaN-buffer and with iron-doped GaN-buffer were analyzed. The device OFF-state drain leakage was reduced for high drain voltages and the maximum breakdown strength was increased from 520 to 880 V for iron-doped GaN-buffer devices. Static device characteristics and the dynamic ON-state resistance of devices fabricated on pre-implanted SiC substrates are not degraded. High Resolution X-ray Diffraction (HRXRD) analysis confirms in coincidence that the GaN buffer defect density is not increased. Substrate implantation is thus beneficial for low-leakage high-voltage GaN devices on n-type SiC substrates.