Crystallographic studies of some mixed thiogallate semiconductors

Abstract

A crystallographic study has been made of solid solutions of the tetragonal defect chalcopyrites (14), CdGa₂S₄ and CdGa₂Se₄. The compositions may be represented by CdGa₂S_4(1-x)Se_4x where x=0.0, 0.25, 0.50, 0.75 and 1.0. A complete solid solubility was observed between these two compounds. The a-axis values varied linearly with composition, whilstc-axis values initially showed a slower rise for x<0.5 and then a marked rapid rise with increasing selenium content. Single crystals were grown of these compositions by the chemical transport method. Optimum conditions required for the growth of the crystals have been established. The crystals of CdGa₂S₄ and CdGa₂S₃Se had the biggest face parallel to (001) plane whereas crystals of compounds CdGa₂S₂Se₂, CdGa₂SSe₃ and CdGa₂Se₄ were triangular prisms with a face parallel to (112) plane and lang110rang as the growth axis. The parameters x, y andz for selenium position in CdGa₂Se₄ were obtained by comparing the calculated values of F² factors with those obtained from observed intensities. The best match was found forx=y=0.25 andz=0.15.