Interdiffusion of CdS/CdTe thin films: Modeling x-ray diffraction line profiles

A method for analyzing the diffusion process for CdS into CdTe thin films using x-ray diffraction is presented, allowing both bulk and grain boundary diffusion coefficients to be estimated. The equilibrium phase diagram for the ${\mathrm{CdTe}}_{\text{1−x}}{\mathrm{S}}_x$ and ${\mathrm{CdS}}_{\text{1−y}}{\mathrm{Te}}_y$ alloy system was determined for temperatures from 625 °C to 415 °C. Measured diffraction line profiles for time-progressive diffusion of CdS into CdTe films resulting from thermal treatment at 440° were modeled using bulk and grain boundary diffusion coefficients of ${\text{1.25×10}}^{\text{−13}} {\mathrm{cm}}^{\mathrm{2}}\mathrm{/s}$ and ${\text{1.5×10}}^{\text{−8}} {\mathrm{cm}}^{\mathrm{2}}\mathrm{/s},$ respectively. Modeling diffraction line profiles of samples treated at temperatures from 380 °C to 480 °C yielded Arrhenius activation energies for bulk and grain boundary diffusion processes of 2.8 eV and 2.0 eV, respectively. The bulk diffusion coefficients obtained from thin film structures were comparable to those obtained by Auger depth profiles for CdS/CdTe couples using CdTe single crystals.