C-V and J-V investigation of HfO2/Al2O3 bilayer dielectrics MOSCAPs on (100) β-Ga2O3

In this letter, MOS capacitors with bilayer dielectrics consisted of large bandgap Al2O3 and high-k HfO2 in different stacking order on n-type doped (100) β-Ga2O3 are investigated through C − V and J − V measurement. The C − V measurement results reveal that incoming HfO2 makes both bilayer structures attain an increasing dielectric constant, which means a better gate control ability in transistors comparing with single Al2O3. Additionally, the interface state density extracted by high-low frequency capacitance method suggests that Al2O3/(100)β-Ga2O3 with no treatment shows a comparative Dit value (8.0 × 1012 cm-2eV-1 to 2.2 × 1011 cm-2eV-1) with HfO2/(100)β-Ga2O3 (8.4 × 1012 cm-2eV-1 to 1.0 × 1011 cm-2eV-1) in energy range of 0.2 to 0.9 eV. Furthermore, HfO2/Al2O3/Ga2O3 showing a bigger forward breakdown voltage of 11.0 V than 7.8 V of Al2O3/HfO2/Ga2O3 demonstrates that inserted larger bandgap Al2O3 insulator between Ga2O3 semiconductor and high-k HfO2 dielectric can prevent gate leakage current more effectively. Accordingly, the HfO2/Al2O3/Ga2O3 can enhance gate control ability with an acceptable gate breakdown voltage and become an alternative choice in the design of the gate structure for Ga2O3 MOSFETs.