Near-field photocurrent measurements on boron-implanted silicon

We report near-field photocurrent (NPC) measurements performed on three boron-implanted silicon samples characterized by different implantation doses. The images were acquired at λ=1330 nm corresponding to a photon energy of 0.93 eV which is smaller than the silicon energy gap (Egap=1.12 eV), representing incident radiation to which silicon is virtually transparent. The NPC images reveal the presence of boron clusters which are a consequence of B implantation and rapid thermal annealing at 1100 °C for 30 s. Boron clusters behave as metal clusters embedded into the silicon matrix and introduce gap states which give rise to the observed photocurrent.