Amorphous to crystalline phase transformation and growth of thin Te-Se films

Abstract

The crystallization of amorphous TeSe-alloy thin films on a carbon substrate occurs by the nucleation and subsequent growth of small single crystalline nuclei with hexagonal structure. The main orientation of these nuclei are with their c axis parallel to the substrate. Isothermal growth rates give an activation energy of 0.7 eV for the growth of the crystalline phase. The morphology of the growing crystallites shows some crystallographic faceting but no preferred c-axis growth. It is proposed that crystal growth takes place by the addition of small segments of extended homogeneous chains of either Te or Se atoms onto specific low energy crystallographic planes. This growth mechanism plus the difference in specific volumes of the crystalline phase compared to the amorphous phase give rise to built-in stresses in the thin crystallized film which might be detrimental when used for device applications.