Tunnel field-effect transistors were fabricated from axially doped silicon nanowire p-n junctions grown via the vapor-liquid-solid method. Following dry thermal oxidation to form a gate dielectric shell, the nanowires have a p-n-n(+) doping profile with an abrupt n-n(+) junction, which was revealed by scanning capacitance microscopy. The lightly doped n-segment can be inverted to p(+) by modulating the top gate bias, thus forming an abrupt gated p(+)-n(+) junction. A band-to-band tunneling current flows through the electrostatically doped p(+)-n(+) junction when it is reverse biased. Current-voltage measurements performed from 375 down to 4.2 K show two different regimes of tunneling current at high and low temperatures, indicating that there are both direct band-to-band and trap-assisted tunneling paths.

Nickel germanide contacts are expected to play an important role in Ge-based electronics similar to that of their nickel silicide counterparts in Si devices. Here we have studied the solid state reaction between Ni contact pads and Ge nanowires. We observe the formation of axial nickel germanide segments after annealing at temperatures as low as 300 °C for 2 min. The nickel germanide segments are polycrystalline, without an epitaxial relationship to the Ge nanowire, in contrast to observations of epitaxial nickel silicide formation from Si nanowires. The crystal structure of the nickel germanide phase is consistent with the Ni2In prototype structure. Annealing above 400 °C results in fracture in the nickel germanide segment; however, nickel germanide segments as long as 1.7 μm can be formed by annealing at 400 °C for 5 min.

Abstract

No abstract

The effect of growth conditions on the composition of Si1-xGex nanowires fabricated by vapor-liquid-solid growth using Si2H6 and GeH4 sources was investigated. The use of Si2H6 resulted in an increase in Si incorporation in the Si1-xGex nanowires at lower growth temperatures compared to SiH4 which is more commonly used. A wide range of Ge compositions from ~20-80% was achieved by changing the inlet gas ratio at a constant temperature in the range of 350-425ºC. Using these conditions, Ge/Si1-xGex axial heterostructured nanowires were also fabricated at 375ºC with Ge compositions of 92% and 66% in the SiGe segment and the morphology and interfacial compositional profile of the nanowires were examined.