Low resistivity of Si-doped <i>n</i> -type Al0.68Ga0.32N on sapphire by two-step growth for high power electronics

Al-rich AlGaN is a promising material for deep-ultraviolet (UV) optoelectronics and high-power electronics, but achieving efficient n-type conductivity on cost-effective sapphire substrates remains a key challenge due to high dislocation densities, defect-assisted compensation, and limited dopant activation. In this work, we investigate Si doping in Al0.68Ga0.32N grown by metal–organic vapor-phase epitaxy and elucidate the compensation mechanisms that constrain conductivity. Cathodoluminescence analysis reveals the appearance of a ∼2.6 eV emission band linked to cation–vacancy complexes involving Si (VIII–n·SiIII), which coincides with a sharp reduction in carrier concentration when the Si-doped AlGaN layer is grown at a moderately high temperature. To mitigate these limitations, we develop a two-step growth approach: a high-temperature non-intentionally doped AlGaN layer that reduces structural defects and improves surface morphology, followed by a low-temperature Si-doped AlGaN layer that suppresses compensation from VIII–n·SiIII complexes. This strategy yields a record-low resistivity of 1.09 × 10−2 Ω cm in Al0.68Ga0.32N on sapphire. These results demonstrate a practical pathway for overcoming doping limits in high-Al-content AlGaN using sapphire, enabling scalable high-performance UV optoelectronic and electronic devices.