NONOHMIC HOPPING CONDUCTION IN NANOFABRICATCD SI POINT CONTACTS

Using nanofabrication techniques we made Si point contacts with constr iction sizes down to 85 nm and investigated their I-V curves at temper atures between 300 K and 200 mK. At room temperature the devices are o hmic and obey the Maxwell resistance. Below 40 K the type of conductio n at low electric fields is Mott-variable range hopping. At higher fie lds an intriguing non-ohmic behaviour was found which is related to fo rmation of a spherical region of non-ohmic hopping conduction, centred around the constriction of the point contact. In this regime, the vol tage 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.