Current-voltage characteristics of silicon-doped GaAs nanowhiskers with a protecting AlGaAs coating overgrown with an undoped GaAs layer

A technique for measurement of longitudinal current-voltage characteristics of semiconductor nanowhiskers remaining in contact with the growth surface is suggested. The technique is based on setting up a stable conductive contact between the top of a nanowhisker and the probe of an atomic-force microscope. It is demonstrated that, as the force pressing the probe against the top of the nanowhisker increases, the natural oxide layer covering the top is punctured and a direct contact between the probe and the nanowhisker body is established. In order to prevent nanowhiskers from bending and, ultimately, breaking, they need to be somehow fixed in space. In this study, GaAs nanowhiskers were kept fixed by partially overgrowing them with a GaAs layer. To isolate nanowhiskers from the matrix they were embedded in, they were coated by a nanometer layer of AlGaAs. Doping of GaAs nanowhiskers with silicon was investigated. The shape of the current-voltage characteristics obtained indicates that introduction of silicon leads to p-type conduction in nanowhiskers, in contrast to n-type conduction in bulk GaAs crystals grown by molecular-beam epitaxy. This difference is attributed to the fact that the vapor-liquid-solid process used to obtain nanowhiskers includes a final stage of liquid-phase epitaxy, a characteristic of the latter being p-type conduction obtained in bulk GaAs(Si) crystals.