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
_0.958
Sn
_0.042
p-channel metal-oxide-semiconductor field-effect transistors (pMOSFETs) on surface orientations. Compressively strained Ge
_0.958
Sn
_0.042
channels were grown on (100) and (111) Ge substrates. Sub-400°C Si
₂
H
₆
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.