Room temperature photo-response of titanium supersaturated silicon at energies over the bandgap

Silicon samples were implanted with high Ti doses and subsequently processed with the pulsed-laser melting technique. The electronic transport properties in the 15–300 K range and the room temperature spectral photoresponse at energies over the bandgap were measured. Samples with Ti concentration below the insulator-metal (I-M) transition limit showed a progressive reduction of the carrier lifetime in the implanted layer as Ti dose is increased. However, when the Ti concentration exceeded this limit, an extraordinary recovery of the photoresponse was measured. This result supports the theory of intermediate band materials and is of utmost relevance for photovoltaic cells and Si-based detectors.

Insulator-to-metal transition in vanadium supersaturated silicon: variable-range hopping and Kondo effect signatures

We report the observation of the insulator-to-metal transition in crystalline silicon samples supersaturated with vanadium. Ion implantation followed by pulsed laser melting and rapid resolidification produce high quality single-crystalline silicon samples with vanadium concentrations that exceed equilibrium values in more than 5 orders of magnitude. Temperature-dependent analysis of the conductivity and Hall mobility values for temperatures from 10K to 300K indicate that a transition from an insulating to a metallic phase is obtained at a vanadium concentration between 1.1 × 10^(20) and 1.3 × 10^(21) cm^(−3) . Samples in the insulating phase present a variable-range hopping transport mechanism with a Coulomb gap at the Fermi energy level. Electron wave function localization length increases from 61 to 82 nm as the vanadium concentration increases in the films, supporting the theory of impurity band merging from delocalization of levels states. On the metallic phase, electronic transport present a dispersion mechanism related with the Kondo effect, suggesting the presence of local magnetic moments in the vanadium supersaturated silicon material.