Non-ohmic hopping conduction in nanofabricated Si point contacts

Abstract

Using nanofabrication techniques we made Si point contacts with constriction sizes down to 85 nm and investigated their I—V curves at temperatures between 300 K and 200 mK. At room temperature the devices are ohmic and obey the Maxwell resistance. Below 40 K the type of conduction at low electric fields is Mott-variable range hopping. At higher fields an intriguing non-ohmic behaviour was found which is related to formation of a spherical region of non-ohmic hopping conduction, centred around the constriction of the point contact. In this regime, the voltage at the electrodes is shown to vary as V( I) = I c R M(2( I/ I c) 1/2 −1), which is specific for the point contact geometry.