Germanium–Tin (GeSn) p-Channel MOSFETs Fabricated on (100) and (111) Surface Orientations With Sub-400 $^{\circ}\hbox {C} \hbox {Si}_{2}\hbox {H}_{6}$ Passivation

In this letter, we report the first study of the dependence of carrier mobility and drive current I_Dsat of Ge_0.958Sn_0.042 p-channel metal-oxide-semiconductor field-effect transistors (pMOSFETs) on surface orientations. Compressively strained Ge_0.958Sn_0.042 channels were grown on (100) and (111) Ge substrates. Sub-400°C Si₂H₆ treatment was introduced for the passivation of the GeSn surface prior to gate stack formation. Source/ drain series resistance and subthreshold swing S were found to be independent of surface orientation. The smallest reported S of 130 mV/decade for GeSn pMOSFETs is achieved. The (111)-oriented device demonstrates 13% higher IDsat over the (100)oriented one at a V_GS-V_TH of -0.6 V and V_DS of -0.9 V. We also found that GeSn pMOSFETs with (111) surface orientation show 18% higher hole mobility than GeSn pMOSFETs with (100) orientation.