The effect of grown-in structural imperfections on the radiation defect formation and annealing in dislocation-free silicon

Abstract

The processes of radiation defect formation and annealing in dislocation-free n-type Si (ϱ = 100 Ω cm) grown by the float-zone technique in argon atmosphere or in vacuum are studied. In the latter case the ingot is grown at a varying rate and therefore contains A-, A + B-, and D-type microdefects in different parts. Crystals obtained in argon atmosphere do not involve microdefects identified by selective etching. The temperature dependences of the charge carrier lifetime (τ) and the Hall coefficient (RH) are measured. The variation in τ and RH after 60Co γ-ray irradiation at T = 330 K is found to be due to the accumulation of E-centres with the level Ec −0.43 eV. However, the E-centre introduction efficiency and annealing temperature in Si grown in argon atmosphere as well as in crystals with A + B-type microdefects are lower than in control Si with small content of dislocations (ND = 1 × 104 cm−2) where microdefects are absent. It is concluded that under certain growing conditions (gaseous atmosphere, growth rate, axial temperature gradient) of dislocation-free crystals, shallow (according to the estimates of 10 to 20 atoms) interstitial-type inclusions unidentified by selective etching can be formed in their bulk which produce strain fields around themselves and thereby are surrounded by an impurity atmosphere. Affected by the strain fields induced by inclusions, primary radiation defects migrate directedly towards them whereby accumulation of secondary complexes occurs around inclusions within the impurity atmosphere. For the same reason the E-centre formation efficiency in crystal matrix decreases and their annealing parameters change due to the effect to strain fields. Inclusions are assumed to be predecessors (fragments) of B- or D-type microdefects. [Russian Text Ignored].