【Member Papers】 National Yang Ming Chiao Tung University --- Study on Metal-Oxide Field Effect Transistors of β-Gallium Oxide with AlGaO Spacer Layer Grown on Sapphire for High-Power Device Applications

      Researchers from the National Yang Ming Chiao Tung University have published a dissertation titled "Study on Metal-Oxide Field Effect Transistors of β-Gallium Oxide with AlGaO Spacer Layer Grown on Sapphire for High-Power Device Applications" in ACS Applied Electronic Materials.

Project Support

      The authors wish to express their sincere gratitude for the financial support by the Higher Education Sprout Project of the National Yang Ming Chiao Tung University and the Ministry of Education (MOE), Taiwan and 2024 MOE UI-UAAT Cooperation Project. The authors also acknowledge the Industrial Technology Research Institute and MAtek Corporation for funding and material measurement support.

Abstract

      This study utilized metal–organic chemical vapor deposition technology to grow β-Ga₂O₃ epitaxial layers on sapphire substrates and fabricate lateral β-Ga₂O₃ field-effect transistors (FETs). To enhance the performance of these FETs, a β-Ga₂O₃/(Al_0.33Ga_0.67)₂O₃ structure was incorporated. The resulting FETs demonstrated high on-state current (I_on), low on-state resistance (R_on), and a high on–off ratio of drain current, indicating excellent two-dimensional electron gas (2DEG) characteristic offered by β-Ga₂O₃/(Al_0.33Ga_0.67)₂O₃ structure. By optimization of the thickness and doping concentration of β-Ga₂O₃, high-performance 2DEG β-Ga₂O₃ FETs were achieved, which satisfied the stringent requirements for power devices. Notably, the heavily doped β-Ga₂O₃/(Al_0.33Ga_0.67)₂O₃ structure led to a significant improvement in performance, with the saturation current (I_D,sat) increasing from 0.16 to 11.4 mA/mm, a remarkable 6925% increase, and the breakdown voltage rising from 331 to 687 V, an increase of 107.25%. The relative performance of the device with and without AlGaO was also simulated. These enhancements were primarily due to the effective reduction of leakage current density and 2DEG formation by the β-Ga₂O₃/(Al_0.33Ga_0.67)₂O₃ layer, which was grown by the importance of precise growth parameters and structural design in advancing the performance of β-Ga₂O₃ FETs, making them highly promising for high-power applications.

Conclusions

      In this study, 2DEG Ga₂O₃ FETs have been demonstrated. 2DEG is enhanced by a higher carrier concentration of a β-Ga₂O₃ layer resulting in the V_T shift of β-Ga₂O₃ FETs with higher on-current. The excellent on-current, gate control (I_on/I_off > 10⁷), and higher breakdown voltage are achieved by the 2DEG channel with optimized carrier concentration and thickness of the β-Ga₂O₃ epitaxy structure. The structures with and without AlGaO were also simulated by TCAD. The obtained results were very consistent with the experiment results. All of these results suggest that the proposed AlGaO/β-Ga₂O₃ FET is promising for high-voltage device applications.