AlGaN/GaN high electron mobility transistorwith Al₂O₃+BCB passivation

In this paper, Al₂O₃ ultrathin film used as the surface passivation layer for AlGaN/GaN high electron mobility transistor (HEMT) is deposited by thermal atomic layer deposition (ALD), thereby avoiding plasma-induced damage and erosion to the surface. A comparison is made between the surface passivation in this paper and the conventional plasma enhanced chemical vapor deposition (PECVD) SiN passivation. A remarkable reduction of the gate leakage current and a significant increase in small signal radio frequency (RF) performance are achieved after applying Al₂O₃+BCB passivation. For the Al₂O₃+BCB passivated device with a 0.7 μ gate, the value of f_max reaches up to 100 GHz, but it decreases to 40 GHz for SiN HEMT. The f_max/f_t ratio (≥ 4) is also improved after Al₂O₃+BCB passivation. The capacitance-voltage (C-V) measurement demonstrates that Al₂O₃+BCB HEMT shows quite less density of trap states (on the order of magnitude of 10¹⁰ cm^-2) than that obtained at commonly studied SiN HEMT.