Atom-Scaled Hafnium Doping for Strengthening the Germanium Oxide Interfacial Layer of The Gate Stack of Germanium P-Type Metal-Oxide-Semiconductor Field Effect Transistor

We have developed a method that uses a half-cycle Hf precursor adsorption to subtly dope GeO₂ IL of the Hf-based gate stack through in situ plasma-enhanced atomic layer deposition. This technique can effectively reduce GeO vaporization and improve the thermal stability of the GeO₂ layer. Our results indicated that the accumulation capacitance (C_acc) undergoing higher temperatures showed no noticeable increase in the capacitance-voltage (CV) curves once Hf was delicately introduced into the GeO₂ layer. According to the Ge 3d spectra of X-ray photoelectron spectroscopy, we found that the IL had a signal from extra Hf-O bonds; thus, we conclude GeO evaporation can be suppressed substantially by Hf incorporation. As a result, adding metal into GeO_x IL to form HfGeO_x achieved a remarkably low leakage current of 9 × 10⁻⁵ A cm⁻² and the lowest interface trap density (D_it) of approximately 2 × 10¹¹eV⁻¹ cm⁻² at 500 °C of PMA. In addition, applying this gate stack structure to device fabrication significantly reduced the leakage current of the off-state and improved the effective peak hole mobility.