Ge/Si nanowire heterostructures as high-performance field-effect transistors

Semiconducting carbon nanotubes(1,2) and nanowires(3) are potential alternatives to planar metal-oxide-semiconductor field-effect transistors (MOSFETs)(4) owing, for example, to their unique electronic structure and reduced carrier scattering caused by one-dimensional quantum confinement effects(1,5). Studies have demonstrated long carrier mean free paths at room temperature in both carbon nanotubes1,6 and Ge/Si core/shell nanowires(7). In the case of carbon nanotube FETs, devices have been fabricated that work close to the ballistic limit(8). Applications of high-performance carbon nanotube FETs have been hindered, however, by difficulties in producing uniform semiconducting nanotubes, a factor not limiting nanowires, which have been prepared with reproducible electronic properties in high yield as required for large-scale integrated systems(3,9,10). Yet whether nanowire field-effect transistors (NWFETs) can indeed outperform their planar counterparts is still unclear(4). Here we report studies on Ge/Si core/shell nanowire heterostructures configured as FETs using high-kappa dielectrics in a top-gate geometry. The clean one-dimensional hole-gas in the Ge/Si nanowire heterostructures(7) and enhanced gate coupling with high-kappa dielectrics give high-performance FETs values of the scaled transconductance (3.3 mS mu m(-1)) and on-current (2.1 mA mu m(-1)) that are three to four times greater than state-of-the-art MOSFETs and are the highest obtained on NWFETs. Furthermore, comparison of the intrinsic switching delay, tau = CV/I, which represents a key metric for device applications(4,11), shows that the performance of Ge/Si NWFETs is comparable to similar length carbon nanotube FETs and substantially exceeds the length-dependent scaling of planar silicon MOSFETs.