Dielectric functions evolution and electronic bandgap manipulation by silicon doping for Sb₂Te₃phase change films: Temperature dependent spectroscopic ellipsometry study

The dielectric function evolution and electronic bandgap manipulation by silicon (Si) doping for Sb 2 Te 3 phase change films have been investigated by temperature dependent spectroscopic ellipsometry measurements. During the phase change from amorphous to rhombohedral structures, the significant contrast of electronic band structure for pure Sb 2 Te 3 and Si-doped Sb 2 Te 3 (SST) films as functions of temperature (210-620 K) and Si concentration (0%-12%) has been systematically studied by analyzing the dielectric functions, Tauc gap energy, and partial spectral weight integral. The distinct differences can be mainly attributed to the increment of structure order degree, originated from the change of local bonding arrangement. Based upon the evolutions of Tauc gap energy and partial spectral weight integral with increasing temperature for all four samples, it can be concluded that Si doping can inhibit the crystallization of amorphous films and accelerate the phase change process by serving as nanoscale heaters, which is helpful in improving the thermal stability of amorphous films. The elevated crystallization temperature and phase change rate by Si doping contribute to the dependability and endurance for SST-based phase change memory. The present data provide an important direction on the physical mechanism investigation of Si doping Sb 2 Te 3 by optical techniques.