In this work the difference of annealing behaviors of VO (A-center) in varied doses of neutron-irradiated Czochralski silicon (S1: (5 x 10(17) n/cm(2)) and S2: (1.07 x 10(19) n/cm(2))) was studied. The vacancy-oxygen complex (VO) is one of the main defects formed in neutron-irradiated Czochralski silicon (CZ-Si). In this defect, the oxygen atom shares a vacancy, it is bonded to two silicon neighbors. Annealed at 200 degrees C, divacancies are trapped by O-i to form the V2O (840 cm(-1)). With the decrease in the 829 cm(-1) (VO) three infrared absorption bands at 825, 834 and 840 cm(-1) (V2O) rise after being annealed at the temperature range of 200-500 degrees C. After being annealed at 450-500 degrees C the main absorption bands in the S1 sample are 834, 825 and 889 cm(-1) (VO2), and 825 and 919.6 cm(-1) (O-V-O) in S2. Annealing of the A-center in varied neutron-irradiated CZ-Si consists of two processes. The first is trapping of VO by interstitial oxygen (O-i) in low-dose neutron-irradiated CZ-Si (SI) and the second is capturing of the wandering vacancy by VO, etc, in high-dose neutron-irradiated CZ-Si (S2). The VO2 and O-V-O defects play an important role in the annealing of the A-center. With the increase in the irradiation dose, the annealing behavior of the A-center is changed and the formation of the VO2 is depressed. (c) 2005 Elsevier B.V. All rights reserved.