Study of SiGeAsTe and SiGeAsSe chalcogenide thin films by Raman spectroscopy and understanding of their OTS properties

In this paper, a range of sputtered ternary and quaternary (Si)(Ge)As${}_x$Te${}_3$ layers (x: 2 or 5) and (Si)(Ge)As${}_2$Se${}_3$ layers are examined using Raman spectroscopy. The results are linked to the Ovonic Threshold Switching properties of these materials when incorporated in selector devices, as observed in separate studies. In case of both the As-rich and As-poor tellurides, a large amount of homopolar bonds are present as the spectra are dominated by peaks associated with As–As and Te–Te bonds. Such homopolar bonds are commonly linked with drift in OTS properties. In the case of the selenides the spectra are dominated by modes associated with heteropolar As–Se bond vibrations. Adding Ge as an alloying element has a significant impact on the bond structure for both material systems. In contrast, Si has a much less pronounced impact and will mostly bond with itself. Time-resolved Raman measurements were also performed to determine the stability of the layers under micro-Raman laser excitation. At the regular exposure settings, no significant changes in the spectra were observed during the measurement. At elevated exposure settings, however, persistent changes in the bond structure can be induced for certain compositions.