Compositions, structures, and mid-infrared transparency of Sb-Te-Se thin films synthesized using a combinatorial method

The dielectric function of phase-change materials (PCMs) presents a tremendous difference for the amorphous and crystalline states. Therefore, the measurement of the mid-infrared transparency of thin films of PCMs will provide a cost-efficient method to reveal the dependence of amorphous-crystalline phase transition on their compositions. Although Sb-Te-Se system has shown the advantages of the high speed, low power consumption and long retention life, the information on the mid-infrared transparency of Sb-Te-Se thin films is still insufficient. In our investigation, combinatorial materials libraries of Sb-Te-Se thin films were synthesized. The composition and mid-infrared spectral transmittance of each pixel of Sb-Te-Se thin film in the library were characterized using the energy dispersive X-ray analysis (EDX) and Fourier-transform infrared (FTIR) spectrometer, respectively. The in-depth chemical composition for randomly selected pixels was identified using secondary ions mass spectroscopy (SIMS). The crystallographic structure of some pixels was also identified using micro-area X-ray diffraction (μ-XRD). It can be found that, with the change of composition in Sb-Te-Se thin films, their mid-infrared spectral transmittance can be organized into three distinctive groups, corresponding to amorphous Sb-Se, Sb${}_2$Se${}_3$ orthorhombic structure and Sb${}_2$Te${}_3$ rhombohedral structure, respectively. Therefore, the amorphous-crystalline phase transition and the phase-change from the orthorhombic structure of Sb${}_2$Se${}_3$ to the rhombohedral structure of Sb${}_2$Te${}_3$ can be completely reflected in the mid-infrared spectral transmittance of Sb-Te-Se thin films.