High-k/GaN interface engineering toward AlGaN/GaN MIS-HEMT with improved V_th stability

Metal–insulator–semiconductor (MIS) capacitor structures were fabricated on AlGaN/GaN two-dimensional electron gas heterostructure material in order to investigate important aspects of the gate module of a corresponding MIS-high electron mobility transistor device. The process sequence started with an initial wet chemical surface treatment of the as-grown semiconductor material followed by an atomic layer deposition of Al₂O₃ (high-k first). The electrical analysis focused on the gate leakage current as well as on the shift of the threshold voltage (V_th) upon bias stress in the off- and the on-state regions. The high-k first samples showed much better V_th stability compared to lithographically processed samples, in which the high-k deposition was performed after ohmic contact formation and just before the gate electrode metallization. These results reflect a superior quality of the high-k/GaN interface for the processed structures according to the high-k first approach.