Enhanced optical properties of Sn-doped Ge2Sb2Te5 thin film with structural evolution

Abstract

The microstructure, texture and optical properties of Sn doped Ge2Sb2Te5 thin films were investigated in this work. The correlation between grain orientation and optical reflectivity of Sn doped Ge2Sb2Te5 thin films has been obtained. Thin films with different compositions were deposited on SiO2/Si (100) wafer using magnetron sputtering method. Both the composition and thickness of thin films were determined using Rutherford backscattering spectrometry (RBS). It appears that face-centered-cubic (fcc) and close-packed-hexagonal (hcp) structure coexisted in Sn doped Ge2Sb2Te5 thin films. Rietveld structure refinement indicates that the lattice constant of the fcc structure increased with increasing Sn content, while the lattice constant of the hcp structure remains nearly unchanged. Sn doping also leads to the appearance of defects and disordered local arrangement in Ge2Sb2Te5 films. Furthermore, the crystalline optical reflectivity of Sn doped Ge2Sb2Te5 thin films increased, which is attributed to texture formation. The texture component of the hcp structure Ge2Sb2Te5 thin films transformed from cylindrical {01-10} to basal {0001} during the addition of Sn atoms. Accordingly, we proposed a model of texture and optical reflectivity, that is, the basal texture facilitates the high crystalline optical reflectivity of Ge2Sb2Te5 thin films thanks to the six-fold rotational symmetry in the hcp structure.