Surface depletion effect on negative bias stress instability of β -Ga 2 O 3 (100) nanomembrane FETs

In this study, we report on negative bias stress (NBS) instability of bottom-gate β -Ga 2 O 3 (100) field-effect transistors and the effect of surface states reduction by using an atomic layer deposited Al 2 O 3 layer. The fabricated devices exhibit high electrical performance with a field-effect mobility of up to 71.6 cm 2 V −1 · s −1 and a subthreshold slope of ∼0.2 V dec −1 . However, the abnormal positive threshold voltage ( V TH ) shifts under NBS conditions were observed. These phenomena, resulting from the surface depletion effect due to surface defects including dangling bonds and surface states, were moderated and thus the positive V TH shift was altered into a conventional negative shift by using ALD-Al 2 O 3 surface passivation. The results indicate that a high quality passivation layer is suggested to ensure β -Ga 2 O 3 device performance and stability.