Photoconductivity in ion-implanted thin films of Si:In and Si:Tl

The extrinsic photoconductivity of Si:In and Si:Tl is studied on ion-implanted thin films. Additional boron implants are used to compensate the phosphorus substrate doping for obtaining high photocurrents. The spectral photocurrent response and ionisation energies determined are identical in the implanted film and in bulk wafers. The ionisation energiesE _In=157±2 meV andE _Tl=252±2 meV are obtained by a novel evaluation which excludes photothermal excitation via exited bound states.