Impurity-Defect States Reorganization in ZnS under the Influence of N2-Laser Radiation

Abstract

The results of PL investigations of low resistivity (? = 10 Ω cm) ZnS: Al crystals annealed in Bi + BiCl 3 melt for 100 h at 1250 K are presented. The influence of laser radiation annealing (nitrogen laser, P = 1.5 kW, λ = 337.1 nm, t = 10 ns) and heating up to 520 K on PL spectra was studied both from the crystal subsurface and from its volume in the temperature range of 80-520 K. Volume and subsurface spectra were measured from different regions of the cleaved sample surface (normal to two parallel surfaces contacted with the melt). In the PL spectra from ZnS volume radiation bands at 426 nm related to (Cl S ) and 496 nm related to (V Zn Cl S ') were observed. It was supposed that zinc is diffusing from the crystal volume to the Bi melt, increasing the probability of (V Zn Al Zn .) - complex formation. In the subsurface layer (500 μm) Bi' (λ max = 530 nm). V S . and their compensating charge states V Zn could exist. One can suppose that point defect interaction is based on the formation of complexes owing to the diffusion process. They also form complexes owing to quasi-chemical reaction. A destruction of the complexes was observed at T 400 K. As the temperature increases up to 520 K, the intensity of the PL at the subsurface sharply decreases. X-ray investigations under high angles have shown the presence of precipitates of Bi 2 S 3 and BiS 2 chemical compounds. It is shown that as a result of ZnS: Al: Bi crystal laser illumination and low temperature heating (up to 520 K) in the subsurface layer impurity defect state (IDS) reorganization and new (Bi 2 S 3 ; BiS 2 ) phase formation occur, which indicates the possible existence of impurity-defect complexes in the different sites of the host crystal. The main mechanisms of IDS change are center recharging and their motion on dislocations under the conditions close to the fluidity limit of the crystal.