Strained GeSn p-Channel Metal–Oxide–Semiconductor Field-Effect Transistors With In Situ Si2H6 Surface Passivation: Impact of Sn Composition

We report a study about the impact of Sn composition on the performance of strained germanium-tin (GeSn) pMOSFETs. GeSn pMOSFETs with Sn compositions of 0.027, 0.040, and 0.075 were fabricated on Ge(001) with an in situ Si₂H₆ passivation. Enhancement in drive current and transconductance is obtained for GeSn pMOSFETs with higher Sn composition due to the smaller capacitance equivalent thickness, the reduced source/drain resistance, and the improved effective hole mobility μeff. Right shift of threshold voltage with Sn composition is observed for the devices. Ge_0.973Sn_0.027, Ge_0.960Sn_0.040, and Ge_0.925Sn_0.075 pMOSFETs demonstrate the peak μ_eff of 340, 378, and 496 cm²/Vs, respectively. At an inversion charge density of 5 × 10¹² cm^-2, Ge_0.925Sn_0.075 pMOSFETs demonstrate 36% and 24% enhancement in μ_eff compared with Ge_0.973Sn_0.027 and Ge_0.960Sn_0.040 devices, respectively. Simulation shows that the enhancement in μeff with Sn composition is resulted from the reduction of hole effective mass and intervalley scattering between heavy and light holes caused by the increased compressive strain.