Effect of thin al₂o₃ surface protection layer on performance improvement of algan/gan hemt

We demonstrate the role of thin Al₂O₃ surface protection layer in improving the device performance of AlGaN/GaN high electron-mobility transistors (HEMTs) The use of the Al₂O₃ surface protection layer also simplifies device process steps in comparison with conventional SiO₂ or Si₃N₄ protection layer. The Al₂O₃ layer is very effective not only in protecting the AlGaN surface during ohmic RTP at high temperature, but also in passivating the AlGaN surface to greatly reduce electron trapping into surface states which leads to improved current collapse. And fabrication of the device with gate length of 0.15 µm exhibited high transconductance of 365 mS/mm and drain current of ~943 mA/mm at VGS = 1 V. The device also exhibited very high RF performances such as f_T and f_max of 68.4 and 129 GHz, with the maximum output power (P_out) of 2.2 W/mm and power added efficiency (P.A.E.) of 27.3%, respectively.