THE STRUCTURE OF GA2TE3 - AN X-RAY AND HIGH-RESOLUTION ELECTRON-MICROSCOPY STUDY

As shown by X-ray and electron diffraction, the structure of Ga2Te3 is confirmed to be of the zinc blende type, with structural vacancies on 1/3 of the Ga sites. But this structure is never perfect: outside normal Bragg reflections, thin streaks along [111]* directions are always seen, joining the Bragg spots, sometimes with a blurred maximum midway between the spots. Such diffraction features indicate some disorder in the stacking of {111} direct lattice planes. Electron microscopy imaging, and particularly high-resolution, reveals planar defects of various lateral extension, whose width is of the order of no more than one Ga2Te3 motif. They are randomly located but in definite {111} orientations. High-resolution images clearly show that these defects cannot be due to antiphase shifts of Ga2Te3 units. A tentative model is proposed, in which the structure is seen as a mosaic of ordered domains limited by defect-boundaries. Each defect-boundary would be due to a random jump in the arrangement of structural vacancies. The local changes of composition in Ga would account for the formation of these defects through a deformation field.