Structural perfection and mechanical properties of ZnSe1-xTex crystals grown by the Bridgman technique

Preparation conditions of ZnSe1-xTex crystals should guarantee stability of their scintillation parameters (light output, after glow, luminescence max imum wavelength), optical uniformity, high mechanical strength and resistan ce to cracking. These crystals were grown by the Bridgman technique under d ifferent degrees of melt overheating and related evaporation of the more vo latile components. Annealing was carried out at 1170-1270 K under zinc vapo r and at 1270 K in argon atmosphere. In this paper studies are reported on the influence of the growth parameters on the distribution of Te along the crystal length, the structural perfection of the grown crystals, and their optical and mechanical properties. Wurtzite-sphalerite transformations occu rring during isothermal annealing of the crystals and their effects upon re sistance to cracking are studied. It can be concluded that the type and concentration of defects, distributio n of tellurium, luminescent and optical characteristics of ZnSe1-xTex grown using the Bridgman method strongly depend on the degree of melt overheatin g. Melt overheating by 50 K ensured crystal uniformity of optical absorptio n. Melt overheating over 100 K led to twin interlayers. With concentration of Te (C-Te) > 0.3%, the sphalerite structure is stabilized and the packing defects due to twinning disappear. The data obtained provide evidence of a positive effect of Te isovalent dopant upon perfection of zinc selenide cr ystals, which is presumable due to stabilization of the sphalerite structur e leading to optical uniformity. The thermal processing of the grown crystals results in almost complete dis appearance of cracking of the material. During this process, the distributi on of an optical transmission on a section of crystals becomes more homogen eous, the magnitude of mechanical strength of a central part essentially in creases and is levelled in all the volume of the material. Possible chemical reactions are considered which lead to the contamination of crystals with an impurity of carbon, resulting in a decrease of transpar ency of scintillator ZnSe1-xTex in the region of intrinsic radiation. (C) 1 999 Elsevier Science B.V. AU rights reserved.