hν-MacEtch of Al-rich AlGaN: Enabling plasma-free processing in the ultra-wide-bandgap regime

Al-rich AlGaN is essential for ultra-wide-bandgap (UWBG) electronics and deep-ultraviolet optoelectronics, yet its processing is limited by the lack of damage-free etching methods. Plasma-based approaches introduce defects, while anisotropic wet etching for GaN often fails at high Al content due to the larger bandgap and stable oxide formation. Here, we demonstrate the first, to our knowledge, plasma-free hν-MacEtch of Al0.6Ga0.4N using a modified HF/(NH4)2S2O8 chemistry that enables stable etching and remains compatible with GaN, allowing a single process across AlGaN/GaN heterostructures. Ohmic contacts formed on hν-MacEtched surfaces show comparable contact resistance but significantly improved uniformity (<5% variation versus >15% using inductively coupled plasma reactive ion etching). These results establish a viable pathway for damage-free, reproducible processing of UWBG nitride materials and devices.