Picosecond photoresponse of carriers in Si ion-implanted Si samples has been measured using femtosecond transient reflectivity measurement. A threshold peak implant dose of 10(16) cm(-2) is required to achieve picosecond carrier lifetime. At this dosage, carrier lifetimes of 0.9 and 1.4 ps are measured for the as-implanted and 400 degrees C annealed Si substrates, respectively. The increase in carrier lifetime upon annealing is attributed to the reduction in the concentration of trap and recombination centers. Sheet resistance also shows a strong dependence on the annealing temperature. An eightfold increase in sheet resistance is obtained for annealed samples, and a reduction in hopping conduction, manifested by the e(-1/T) temperature dependence, may be responsible for the increase in resistance. Further evidence of decreasing hopping conduction can be also observed from the more than two orders of magnitude in reduction of sheet resistance as the peak dosage decreases from 10(16) to 10(14) cm(-2). (C) 1996 American Institute of Physics.
