Ge_0.83Sn_0.17 p-channel metal-oxide-semiconductor field-effect transistors: Impact of sulfur passivation on gate stack quality

The effect of room temperature sulfur passivation of the surface of Ge_0.83Sn_0.17 prior to high-k dielectric (HfO₂) deposition is investigated. X-ray photoelectron spectroscopy (XPS) was used to examine the chemical bonding at the interface of HfO₂ and Ge_0.83Sn_0.17. Sulfur passivation is found to be effective in suppressing the formation of both Ge oxides and Sn oxides. A comparison of XPS results for sulfur-passivated and non-passivated Ge_0.83Sn_0.17 samples shows that sulfur passivation of the GeSn surface could also suppress the surface segregation of Sn atoms. In addition, sulfur passivation reduces the interface trap density D_it at the high-k dielectric/Ge_0.83Sn_0.17 interface from the valence band edge to the midgap of Ge_0.83Sn_0.17, as compared with a non-passivated control. The impact of the improved D_it is demonstrated in Ge_0.83Sn_0.17 p-channel metal-oxide-semiconductor field-effect transistors (p-MOSFETs). Ge_0.83Sn_0.17 p-MOSFETs with sulfur passivation show improved subthreshold swing S, intrinsic transconductance G_m,int, and effective hole mobility μ_eff as compared with the non-passivated control. At a high inversion carrier density N_inv of 1 × 10¹³cm^-2, sulfur passivation increases μ_eff by 25% in Ge_0.83Sn_0.17 p-MOSFETs.