Surface depletion effect on negative bias stress instability of β-Ga2O3 (100) nanomembrane FETs

Abstract

In this study, we report on negative bias stress (NBS) instability of bottom-gate β-Ga2O3 (100) field-effect transistors and the effect of surface states reduction by using an atomic layer deposited Al2O3 layer. The fabricated devices exhibit high electrical performance with a field-effect mobility of up to 71.6 cm2 V−1 · s−1 and a subthreshold slope of ∼0.2 V dec−1. However, the abnormal positive threshold voltage (VTH) 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 VTH shift was altered into a conventional negative shift by using ALD-Al2O3 surface passivation. The results indicate that a high quality passivation layer is suggested to ensure β-Ga2O3 device performance and stability.