Paper EM+2D+SS-WeA4
High Three-terminal Breakdown Voltage Quasi-two-dimensional β -Ga₂O₃ Field-effect Transistors with a Dual Field Plate Structure

Wednesday, October 24, 2018, 3:20 pm, Room 101A

β-Ga₂O₃ is an intriguing material because of its large direct bandgap (4.85 eV), high breakdown field (~8 MV/cm) and excellent thermal and chemical stability. Baliga’s figure of merit of β-Ga₂O₃ is 3214.1, superior to those of other materials such as GaN (846.0) or SiC (317.1). Although β-Ga₂O₃ is not a van der Waals material, β-Ga₂O₃ can be mechanically exfoliated from single crystal substrate into thin layer due to the large anisotropy of the unit cell. Quasi-2D β-Ga₂O₃ devices shows superior electrical properties and robustness in harsh environment, which shows potential of β-Ga₂O₃ as nanoscale power devices. However, quasi-2D β-Ga₂O₃ power devices show premature breakdown due to the electric field concentration. Adopting multiple field plates to relieve the electric field concentration and prevent premature breakdown greatly enhance the performance of power devices, which can be applied to β-Ga₂O₃ nanoelectronic power devices.

H-BN has been used as a dielectric material of 2D devices due to its excellent thermal conductivity and high dielectric constant, as well as atomically flat surface, which can be obtained through mechanical exfoliation. In our work, we used h-BN as a gate field plate dielectric layer by selective transfer on β-Ga₂O₃ channel using PDMS film. SiO₂ dielectric layer was deposited on devices followed by metal deposition for source field plate structure. By applying dual field plate structure, β-Ga₂O₃ devices can show excellent performance in high voltage condition.

β-Ga₂O₃ MESFETs with h-BN gate field plate were fabricated by using the β-Ga₂O₃ and h-BN flakes obtained from respective crystals. Ohmic metal was deposited on mechanically exfoliated β-Ga₂O₃ flakes, followed by precise positioning of exfoliated h-BN flakes on the channel. Gate field plate was fabricated with a part of the electrode overlapped with h-BN. Dual field plate structure was fabricated after deposition of SiO₂ and source field plate metal. Fabricated devices showed excellent output and transfer characteristics even after one month storage, which shows excellent air-stability. Three-terminal off-state breakdown voltage of fabricated device was measured, which shows improvement in breakdown voltage. The electric field distribution was calculated by Silvaco Atlas framework to study the effect of dual field plate on electric field, which explains the improvement of breakdown voltage in those structure. In this study, we present that the performance of β-Ga₂O₃ MESFET as a power device can be improved by adopting dual field plate structure, paving a way to the high-power nanoelectronic β-Ga₂O₃ devices. The details of our work will be discussed in the conference.