Low-temperature conductivity behaviour of ion implanted silicon bolometers

Resistivity measurements carried out in the temperature range 80 mK to 1 K on silicon bolometers - phosphorous doped by ion implantation - at concentrations near the metal-insulator transition, exhibit variable range hopping (VRH) conduction in the whole observed temperature range, with a T-1/2 dependence, in accordance with the Coulomb interaction model for low temperature conductivity in disordered systems. Samples which apparently show a different behaviour, intermediate between VRH and metallic conduction, can be modelled by a metallic resistance in parallel with an active layer which follows the classic exp(To/T)1/2 law. The observed behaviour can be explained in terms of residual radiation damage induced by the ion implantation process. (author)