Performance improvement mechanisms of i-ZnO/(NH4)2Sx-treated AlGaN MOS diodes

► The high quality of i-ZnO film could be deposited by a vapor cooling condensation system. ► The i-ZnO/(NH4)2Sx-treated AlGaN MOS diodes shows low interface density of 2.95 × 1011 cm−2 eV−1. ► The band alignment of the i-ZnO/AlGaN interface was analyzed by XPS and CNL model. ► The band offset of the i-ZnO/AlGaN interface was increased by the (NH4)2Sx surface treatment.