Near-field Imaging of the photocurrent induced by light on boron-implanted silicon

We report near-field photocurrent (PC) measurements performed on boron-implanted silicon and acquired at lambda = 633, 1330, 1550 nm corresponding to photon energies of 1.96, 0.93, and 0.80 eV, respectively. The second and the third energies are below the silicon energy gap (E-gap = 1.12 eV), representing incident radiation to which Si is virtually transparent. The PC images acquired at lambda = 1330 and 1550 nm reveal the presence of boron clusters which are a consequence of B-implantation and rapid thermal annealing at 1100degreesC. Boron clusters behave as metal clusters embedded into the silicon matrix and introduce gap states which give rise to the observed photocurrent. At energies larger than the Si energy gap the near-field PC images give information about subsurface defects not related to boron and with no correspondence in the surface topography.