1School of Mathematics and Physics, Jiangsu University of Technology, Changzhou 213001 2Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093 3State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of MicroSystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050
Abstract：We elucidate the importance of a capping layer on the structural evolution and phase change properties of carbon-doped Ge$_{2}$Sb$_{2}$Te$_{5}$ (C-GST) films during heating in air. Both the C-GST films without and with a thin SiO$_{2}$ capping layer (C-GST and C-GST/SiO$_{2}$) are deposited for comparison. Large differences are observed between C-GST and C-GST/SiO$_{2}$ films in resistance-temperature, x-ray diffraction, x-ray photoelectron spectroscopy, Raman spectra, data retention capability and optical band gap measurements. In the C-GST film, resistance-temperature measurement reveals an unusual smooth decrease in resistance above 110$^{\circ}\!$C during heating. X-ray diffraction result has excluded the possibility of phase change in the C-GST film below 170$^{\circ}\!$C. The x-ray photoelectron spectroscopy experimental result reveals the evolution of Te chemical valence because of the carbon oxidation during heating. Raman spectra further demonstrate that phase changes from an amorphous state to the hexagonal state occur directly during heating in the C-GST film. The quite smooth decrease in resistance is believed to be related with the formation of Te-rich GeTe$_{4-n}$Ge$_{n}$ ($n=0$, 1) units above 110$^{\circ}\!$C in the C-GST film. The oxidation of carbon is harmful to the C-GST phase change properties.
2018, Vol. 35 
