Demonstration of HfO2-Based Gate Stacks with Ultralow Interface State Density and Leakage Current on Ge pMOSFET by Adding Hafnium into GeOx Interfacial Layer

In this work, we investigated a continuous fabrication method for Hf-based gate stacks on a Ge bulk p-type metal–oxide–semiconductor field-effect transistor (pMOSFET) with adding Hafnium atom into GeO
x
interfacial layer (IL) through in situ plasma-enhanced atomic layer deposition (PEALD). The results revealed that the accumulation capacitance exhibited no significant increase in the capacitance-voltage (CV) curves due to the decreased GeO volatilization. Simultaneously, through X-ray photoelectron spectroscopy (XPS), we observed that adding Hf into GeO
x
IL showed a higher GeO content than pure GeO
x
IL. Therefore, adding Hf into GeO
x
IL method could attain an ultralow interface trap density (D
it
) of approximately 2 × 10
¹¹
eV
^–1
cm
^–2
, a record low gate leakage current of 9 × 10
⁻⁵
A/cm
²
under PMA 500 °C. In addition, the Ge pMOSFET with adding Hf into GeO
x
IL at PMA 500 °C exhibited an effective peak hole mobility of 138 cm
²
/V•s owing to less coulomb scattering.