Strained Germanium–Tin (GeSn) P-Channel Metal-Oxide-Semiconductor Field-Effect Transistors Featuring High Effective Hole Mobility

Abstract

Compressively strained \(\hbox {Ge}_{0.973}\hbox {Sn}_{0.027}\) and \(\hbox {Ge}_{0.925}\hbox {Sn}_{0.075}\) p-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) are fabricated with low-temperature \(\hbox {Si}_{2}\hbox {H}_{6}\) surface passivation. High crystallinity GeSn films epitaxially grown on a Ge(001) substrate are used for the device fabrication. The impacts of the Sn composition on the subthreshold swing \(S\), threshold voltage \(V_\mathrm{TH}\), on-state current \(I_\mathrm{ON}\), and effective hole mobility \(\mu _\mathrm{eff}\) of the devices are investigated. GeSn pMOSFETs with different Sn compositions show a similar \(S\), indicating almost the same midgap density of interface states \(D_\mathrm{it}\). A positive shift of \(V_\mathrm{TH}\) with an increase of the Sn composition is observed. A \(\hbox {Ge}_{0.925}\hbox {Sn}_{0.075}\) pMOSFET exhibits a significant improvement in \(I_\mathrm{ON}\) as compared to a device with a lower Sn composition, which is due to the superior hole mobility in a device with a higher Sn composition. \(\hbox {Ge}_{0.925}\hbox {Sn}_{0.075}\) pMOSFETs achieve a peak effective hole mobility \(\mu _\mathrm{eff}\) of \(500\,\hbox {cm}^{2}{\cdot }\hbox {V}^{-1}{\cdot } \hbox {s}^{-1}\), which is much higher than that of \(\hbox {Ge}_{0.973}\hbox {Sn}_{0.027}\) devices. The enhancement of the compressive strain and chemical effect in the channel region with increased Sn composition leads to an improvement of \(\mu _\mathrm{eff}\).