Two-detector coincidence measurements of the Doppler broadened annihilation spectra with a variable energy positron beam are carried out for the study of the annealing behavior of Si implanted with As, P and Cu ions. Different annealing behaviors are observed depending on the ions implanted. In P implanted Si, defect complexes grow in the temperature range up to 400 degreesC. In case of Cu implanted Si, the formation of vacancy-Cu complexes is indicated. Coincidence Doppler broadening (CDB) measurement is a powerful tool for investigation of defects. Though, combination with other techniques is necessary for full utilization of CDB measurements. (C) 2002 Elsevier Science B.V. All rights reserved.