title: Diameter-independent hole mobility in Ge/Si core/shell nanowire field effect transistors.
abstract: Heterostructure engineering capability, especially in the radial direction, is a unique property of bottom-up nanowires (NWs) that makes them a serious candidate for high-performance field-effect transistors (FETs). In this Letter, we present a comprehensive study on size dependent carrier transport behaviors in vapor-liquid-solid grown Ge/Si core/shell NWFETs. Transconductance, subthreshold swing, and threshold voltage exhibit a linear increase with the NW diameter due to the increase of the transistor body size. Carrier confinement in this core/shell architecture is shown to maintain a diameter-independent hole mobility as opposed to surface-induced mobility degradation in homogeneous Ge NWs. The Si shell thickness also exhibits a slight effect on the hole mobility, while the most abrupt mobility transition is between structures with and without the Si shell. A hole mobility of 200 cm(2)/(V · s) is extracted from transistor performance for core/shell NWs with a diameter range of 15-50 nm and a 3 nm Si shell. The constant mobility enables a complete and unambiguous dependence of FET performance on NW diameter to be established and provides a caliper for performance comparisons between NWFETs and with other FET families.
authors.affiliation: Center for Integrated Nanotechnologies, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States.
authors.forename: Binh-Minh
authors.initials: BM
authors.lastname: Nguyen
authors.forename: Yuan
authors.initials: Y
authors.lastname: Taur
authors.forename: S Tom
authors.initials: ST
authors.lastname: Picraux
authors.forename: Shadi A
authors.initials: SA
authors.lastname: Dayeh