Ge pMOSFETs with GeO_x Passivation Formed by Ozone and Plasma Post Oxidation.

Area of Science:

• Materials Science
• Semiconductor Device Physics
• Electrical Engineering

Background:

• Germanium (Ge) pMOSFETs are crucial for advanced electronics, but their performance is limited by interface quality.
• Passivation layers are essential for improving the dielectric/Ge interface in Ge transistors.
• Ozone post oxidation (OPO) and plasma post oxidation (PPO) are investigated as methods to form GeO_x passivation layers.

Purpose of the Study:

• To compare the electrical performance of Ge pMOSFETs using GeO_x passivation layers formed by OPO and PPO.
• To evaluate the impact of different post-oxidation treatments on the dielectric/Ge interface quality.
• To determine the optimal passivation method for enhanced Ge pMOSFET characteristics.

Main Methods:

• Fabrication of Ge pMOSFETs on Al₂O₃/n-Ge (001) substrates with HfO₂ gate dielectric.
• Application of OPO and PPO treatments for GeO_x passivation layer formation.
• Characterization of the dielectric/Ge interface using X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM).
• Electrical performance testing, including threshold voltage (V_TH), on/off current ratio (I_ON/I_OFF), subthreshold swing, and carrier mobility.

Main Results:

• PPO treatment resulted in a positive V_TH shift and a lower I_ON/I_OFF ratio, indicating poor interface quality.
• OPO treatment yielded a higher I_ON/I_OFF ratio (up to 4 orders of magnitude), improved subthreshold swing, and enhanced carrier mobility.
• A thicker Al₂O₃ block layer in the OPO process further increased carrier mobility in Ge transistors.

Conclusions:

• OPO is an effective method for improving the dielectric/Ge interface quality in Ge pMOSFETs.
• The enhanced interface quality achieved through OPO directly contributes to improved effective carrier mobility.
• OPO demonstrates superior performance compared to PPO for fabricating high-performance Ge pMOSFETs.