Optical band gap tuning of Ag doped Ge2Sb2Te5 thin films

Abstract

Thin films of ( Ge2Sb2Te5)100−xAgx (x = 0, 1, 3, 5 and 10) were deposited using thermal evaporation technique. X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy was used to confirm the amorphous nature, uniformity and chemical compositions of deposited films respectively. Transmission spectra divulged the highly transparent nature of films in near infra red region. The average transmission in near infra red region and optical band gap (estimated by Tauc’s plot) was increased with Ag doping upto x = 3 while it decreased for higher values of x. The increase in transmission and optical band gap was attributed to the reduction in density of localized states and vacancies. However, the decrease in the transmission and optical band gap is due to the increase in distortion of the host Ge2Sb2Te5 lattice because Ag is doped at the expense of Ge, Sb and Te. The increased optical band gap could be utilized to reduce threshold current which enhances switching speed in phase change materials.