【International Papers】High breakdown voltage normally off Ga₂O₃ transistors on silicon substrates using GaN buffer

      Researchers from the King Abdullah University of Science and Technology (KAUST) have published a dissertation titled "High breakdown voltage normally off Ga₂O₃ transistors on silicon substrates using GaN buffer" in Applied Physics Letters.

Background

      Beta gallium oxide (β-Ga₂O₃) has emerged as a leading ultrawide bandgap (UWBG) semiconductor material with a bandgap of approximately 4.9 eV, significantly higher than other WBG materials such as silicon carbide (SiC) and gallium nitride (GaN). This large bandgap allows Ga₂O₃ to sustain a critical breakdown field of up to ~8 MV cm^-1, enabling its use in applications that require highvoltage and high-power capabilities. Furthermore, Ga₂O₃ exhibits a high Baliga’s figure of merit, which is a key indicator of power semiconductor performance. These properties make Ga₂O₃ a promising candidate for a wide range of high-power and high-frequency applications, including power electronics, radio frequency (RF) devices, and solar-blind ultraviolet photodetectors. Despite its advantages, several challenges hinder the widespread use of Ga₂O₃ in commercial applications. These include its intrinsically low thermal conductivity, which limits the device’s ability to manage heat during high-power operation, and the difficulty of achieving efficient p-type doping, which is essential for fabricating complementary devices like bipolar junction transistors.

Abstract

      Normally off beta-phase gallium oxide (β-Ga₂O₃) metal-oxide field-effect transistors (MOSFETs) on GaN-on-Si substrates were fabricated with a threshold voltage (V_TH) of 3 V. β-Ga₂O₃ thin films were deposited using pulsed laser deposition. The device demonstrated an excellent breakdown voltage of ∼540 V at V_GS = 0 V and an extremely low gate leakage current of ∼10⁻⁷mA/mm. Additionally, it exhibited a low subthreshold swing (SS) of ∼167 mV/dec and a current on/off ratio of ∼10⁶. The growth and fabrication of β-Ga₂O₃ MOSFETs on GaN-on-Si substrates are significant for high performance and their monolithic integration with GaN devices in future power-integrated circuits.

Summary

      In summary, we have effectively exhibited E-mode β-Ga₂O₃ MOSFETs on GaN buffer layers on Si substrates using PLD growth. The β-Ga₂O₃ MOSFETs have a threshold voltage of 3 V with a high breakdown voltage of ∼540 V at V_GS = 0 V. The devices also showed a low subthreshold swing of ∼167 mV/dec with a low gate leakage current of ∼10⁻⁷mA/mm in the forward bias operation of the transistors. These results highlight the significant potential of β-Ga₂O₃ MOSFETs for high-performance applications, demonstrating that economical and scalable PLD growth of β-Ga₂O₃ thin films on low-cost, commercially available GaN-on-Si substrates can be a promising route for the integration of GaN-based devices in future power and RF electronics.