A high-breakdown-voltage β-Ga2O3 nanoFET with a beveled field-plate structure

Abstract

β-gallium oxide (β-Ga₂O₃) has emerged as a superior power semiconductor material, outperforming GaN and 4H-SiC, owing to its high breakdown field and Baliga's figure-of-merit. Nanoscale β-Ga₂O₃ has compatibility with Si and various two-dimensional materials, offering advanced heterostructure electrical nanodevices. Despite potential advantages, these devices face premature breakdown owing to uneven electric fields. We constructed a β-Ga₂O₃ nanoFET using an h-BN-based angled field-plate (FP) design, which exhibited notably superior breakdown features. The beveled sidewall (60°) of h-BN, a result of downstream SF₆ plasma etching, was employed to re-shape the concentrated electric fields, where the angle of the h-BN was independent of the etch duration owing to the reactivity of the h-BN crystal. The diffusion-limited downstream plasma process with an h-BN etch rate of 0.8 nm s⁻¹ caused nominal damage to both h-BN and β-Ga₂O₃. The electric field concentration on the FP's drain-side edge was reduced by creating a beveled h-BN design, as validated by device simulations. Moreover, the contact with high thermal conductivity h-BN aids in dispersing heat generated in the channel. Excellent n-type field-effect transistor (FET) characteristics were achieved with a current on/off ratio of ∼10⁷, low subthreshold swing of 86.2 mV dec⁻¹, field-effect electron mobility of 14.8 cm² V⁻¹ s⁻¹, and nominal gate leakage currents. The three-terminal breakdown voltage of the β-Ga₂O₃ nanoFET with the angled h-BN FP was obtained at +441 V, surpassing the β-Ga₂O₃ metal–semiconductor field-effect transistor (MESFET) with a straight gate FP. This improvement highlights the potential of β-Ga₂O₃ in high-power devices and attests to the effectiveness of downstream sulfur hexafluoride plasma etching on h-BN.