Two-layer Hall effect model for intermediate band Ti-implanted silicon

Si samples have been implanted with very high Ti doses (over the theoretical Mott limit) to obtain an intermediate band (IB) in the host semiconductor. The electronic transport properties of this material have been analyzed by temperature-dependent sheet resistance and Hall effect measurements in the 7-400 K range. The experimental results are successfully explained by means of an analytical two-layer model, in which the implanted layer and the substrate behave as an IB/n-Si type junction. We deduce that the IB is located at 0.38 eV below the conduction band, which is around one third of the Si bandgap, i.e., theoretically close to the optimum location for an IB. Finally, we obtain that carriers at the IB behave as holes with a mobility of 0.4-0.6 cm(2) V(-1) s(-1). This extremely low mobility is the one expected for a semifilled, metallic band, being this metallic condition of the IB a requirement for IB solar cells