Sub-bandgap absorption in Ti implanted Si over the Mott limit

We have analyzed the structural and optical properties of Si implanted with very high Ti doses and subsequently pulsed-laser melted (PLM). After PLM, all samples exhibit an abrupt and roughly uniform, box-shaped Ti profile, with a concentration around 2 x 10(20) cm(-3), which is well above the Mott limit, within a 150 nm thick layer. Samples PLM-annealed at the highest energy density (1.8 J/cm(2)) exhibit good lattice reconstruction. Independent of the annealing energy density, in all of the samples we observe strong sub-bandgap absorption, with absorption coefficient values between 4 x 10(3) and 10(4) cm(-1). These results are explained in terms of the formation of an intermediate band (IB) originated from the Ti deep levels.