Direct Probing of Schottky Barriers in Si Nanowire Schottky Barrier Field Effect Transistors

This work elucidates the role of the Schottky junction in the electronic transport of nanometer-scale transistors. In the example of Schottky barrier silicon nanowire field effect transistors, an electrical scanning probe technique is applied to examine the charge transport effects of a nanometer-scale local top gate during operation. The results prove experimentally that Schottky barriers control the charge carrier transport in these devices. In addition, a proof of concept for a reprogrammable nonvolatile memory device based on band bending at the Schottky barriers will be shown.

Figure 1

Schematic of the SGM setup. The ${\mathrm{NiSi}}_2$ electrodes act as the source and drain. The Si substrate is the back gate, and the conductive AFM Tip is the scanning top gate.

Figure 2

(a) SEM micrograph of the NW. Source and drain Ni contacts are visible on the top and bottom of the image. The ${\mathrm{NiSi}}_2$ parts of the NW are brighter than the Si part. Another nanowire on the top left is not contacted to both electrodes and therefore not the subject of this work. (b) AFM topography map of the same NW. (c) Profiles 1–5 correspond to the positions in (b) and show different diameters.

Figure 3

(a) Transfer characteristics of the SiNWSBFET with $V_D=-1\mathrm{V}$ measured on a probe station. The horizontal lines mark the current range of the SGM setup. (b) Band diagram schematic of hole tunneling through the Schottky junction at an applied back gate bias. (c),(d) The transfer characteristics measured in the SGM setup under the same conditions before and after SGM. The shaded areas mark the gate bias range affected by the top gate bias during the corresponding SGM measurement (II–V) at the $V_{\mathrm{BG}}$ marked by the corresponding line.

Figure 4

(a) Topography map of the Si NW. The slight distortion of the NW is caused by the NW being moved by the tip. (b) Current map of the same area. The area marked with a red rectangle was enlarged and contrast was adjusted to display negative currents. The band diagram schematically depicts local band bending with just the back gate in black and with the additional top gate over the right Schottky junction in red.

Figure 5

SGM maps after interchanging the source and drain. Left: Topography map of the Si NW. Right: Current map of the corresponding area. The band diagrams schematically depict the band bending with just a BG (black) and with an additional TG (red) over the corresponding Schottky junction.