THE BEHAVIOR OF RADIATION-DAMAGE OF NB-IMPLANTED SAPPHIRE AFTER ANNEALING AT REDUCING ATMOSPHERE( ION)

Sapphire crystals with (0001) and (01 (1) over bar 2) orientations wer e implanted with 380 keV Nb+ ions to a dose of 5 x 10(16) ions/cm(2) a t room temperature and 100 K. The behavior of the radiation damage pro duced by ion implantation followed by annealing with a series of steps from 500 to 1100 degrees C at reducing atmosphere is investigated usi ng optical absorption technique. The absorption curves were evaluated by Gaussian fitting based on the well known F-type centers, which were confirmed by luminescence measurements. The results of optical densit y (OD) from the bands with annealing: temperature and time show that t he annealing behavior of the radiation damage produced by Nb+ ion impl antation call be divided into three stages. The First stage is in tile range of annealing from 500 to 800 to 900 degrees C; the second is fr om 900 to 1000 degrees C: the third is one above 1000 degrees C. Defec ts mere annealed within these stages due to different mechanisms which are proposed on the basis of the optical absorption measurements comb ined with the observation of SEM micrographs and colour variation of t he sample after annealing steps with temperature.