Multiple contacts investigation of single silicon nanowires with the active voltage contrast scanning electron microscopy technique

Abstract

A method for analysing the formation of electrical contacts to single silicon nanowires (Si NWs) by exploiting scanning electron microscopy (SEM) images, using active secondary electrons voltage contrast, is presented. Our approach clearly demonstrates the advantages of the proposed technique in analysing multiple contacts to a single nanowire simultaneously, in comparison to the conventional voltage contrast technique, where only two contact structures can be analysed, mainly for studies of the material dopant’s profile. The SEM is equipped with an in-lens detector, which collects the secondary electrons generated during electron beam exposure of the sample. Biasing the contacts with different voltages has been used to analyse the metal to Si NW contacts. The secondary electrons are sensitive to the potential distribution and the contrast of the SEM image changes depending on the number of secondary electrons detected. The Si NWs also vary their contrast together with the electrodes if they are properly electrically contacted. The basic tools and fixtures required for such measurements, and the corresponding image processing algorithms are described.

Voltage Contrast in Scanning Electron Microscopy to Distinguish Conducting Ag Nanowire Networks from Nonconducting Ag Nanowire Networks

“…The study has also shown that the PVP-coated part of the AgNWs could be distinguished using the voltage contrast . The voltage contrast is also used to observe other nanowire materials such as Si nanowires and composites comprising carbon nanotubes and insulating polymers. , …”

“…The study has also shown that the PVP-coated part of the AgNWs could be distinguished using the voltage contrast. 23 The voltage contrast is also used to observe other nanowire materials such as Si nanowires 24 and composites comprising carbon nanotubes and insulating polymers. 25,26 In the case of metallic nanowires with concentrations close to the percolation threshold, the degree of charging of nanowires by irradiation of PEs may differ for the isolated nanowires and nanowires in contact with the conductive network.…”

“…The contrast of SEM images depends on the emissivity of secondary electrons (SEs), which is determined by various parameters including the shape of the materials and voltage at the material surface. The contrast in a SEM image caused by a difference in the surface voltage of the material is called “voltage contrast”, − and it can be used for the estimation of the difference in the degree of charging of the material surface caused by charge carrier doping. − SEM measurement causes the charging of the material surface due to the irradiation of primary electrons (PEs). Thus, the difference in the charging of the material surface caused by PE irradiation can be estimated by the voltage contrast.…”