Fermi-level pinning and charge neutrality level in nitrogen-doped Ge2Sb2Te5: Characterization and application in phase change memory devices

Abstract

We study the dependence of the hole barrier height at the metal/α-Ge2Sb2Te5 interface as a function of nitrogen doping in Ge2Sb2Te5 as well as the vacuum work function of the metal. Materials parameters such as the band gap, dielectric constant, and electron affinity values of these nitrogen-doped films were also determined. All Ge2Sb2Te5 films studied in this work are amorphous. Following further physical analysis, the effective work functions of metals on nitrogen-doped Ge2Sb2Te5 films were obtained and found to differ from that of their values in vacuum. This led to the extraction of the slope parameter Sx and charge neutrality level ΦCNL which characterizes Ge2Sb2Te5. Appreciable metal Fermi-level pinning to the charge neutrality level of Ge2Sb2Te5, which is located near the valence band edge, was observed. We then demonstrate application of the extracted parameters to obtain the band alignment of α-Ge2Sb2Te5 with various other materials such as SiO2, giving good agreement with experimental results.