Electronic structure and optical band gap of silver photo-diffused Ge2Sb2Te5 thin film

Thin films of amorphous chalcogenide with composition of Ge22Sb22Te56 (thickness d = 250 nm) and silver film (thickness d = 50 nm) on top of chalcogenide film were deposited by thermal evaporation technique. Photo-diffusion of Ag into the amorphous Ge2Sb2Te5 thin films has been carried out by illuminating the prepared Ge-Sb-Te:Ag bilayer with halogen lamp. The photo-diffused silver depth profile was traced by means of Time of Flight Secondary Ion Mass Spectroscopy. The films remain amorphous after Ag photo-diffusion into the amorphous Ge2Sb2Te5 films. The composition of Ge2Sb2Te5 thin films and the amount of Ag photo-diffused has been gathered from Electron Probe Micro-analyzer having a Wavelength Dispersive Spectrometer. The composition of the films was found to be very close to the bulk used to deposit films and the amount of Ag photo-diffused was ∼5.20 at.%. Changes in the electronic structures of Ge2Sb2Te5 film on Ag photo-diffusion were studied using X-ray photoelectron spectroscopy. The incorporation of silver also increases the optical band gap of the film due to the decrease in the density of defect states on Ag photo-diffusion.