Palwinder Singh

Optical band gap tuning of Ag doped Ge2Sb2Te5 thin films

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.

Optical band gap study of a-Se and Se-Sb thin films

Amorphous selenium (a-Se) and a-Se95Sb5 alloy were prepared using melt quenching technique. X-ray diffraction (XRD) pattern confirmed the amorphous nature of the prepared samples. Composition of the prepared samples has been determined using Energy dispersive X-ray fluorescence (EDXRF) technique. Differential thermal analysis (DTA) confirmed the glassy nature of the prepared samples. Thin films of the prepared samples were deposited on glass substrate using thermal evaporation method. Amorphous nature of the deposited films was confirmed using XRD. Optical properties of these films were obtained from the UV-VIS transmission spectra, at normal incidence, over 200-1100 nm spectral range. The optical absorption edge was described by using the model given by the Tauc. Optical band gap of the deposited films was calculated using Tauc plot. Optical characterization showed that average transmission and optical band gap decreased with the addition of antinomy.

High transmittance contrast in amorphous to hexagonal phase of Ge2Sb2Te5: Reversible NIR-window

Ge2Sb2Te5 (GST) is one of the best phase change materials because of its splendid set of properties, viz., high thermal stability, fast crystallization speed, good endurance, scalability, and reliability. Phase transition [amorphous → face centered cubic (fcc) → hexagonal close packed (hcp)] of GST thin films with annealing was studied using X-ray diffraction. Thin films in amorphous, fcc, and hcp phases are highly, medium, and negligible transparent in the near infra-red region, respectively. The optical transmission in amorphous, fcc, and hcp phases is ∼92%, ∼46%, and ∼2%, respectively, at the wavelength of 2740 nm. At 2740 nm, a high transmission contrast (∼90%) is observed with phase transition from the amorphous to hcp phase. By utilizing large transmission contrast, it is demonstrated that GST can be availed as a potential candidate for reversible near infra-red-window. The sharp change in optical transmission with phase transition can be understood from the change in density of states in the valenc...

Effect of visible light on the optical properties of a-(Ge2Sb2Te5)90Ag10 thin film

(Ge2Sb2Te5)90Ag10 (GST-Ag) bulk alloy was prepared using melt quenching technique. GST-Ag thin film was deposited on glass substrate using thermal evaporation method. The prepared thin films were exposed to visible light (intensity of 105 Lux for 2, 8, 20 and 30 hours) using 25W LED lamp. Transmission spectra were taken using UV-vis-NIR spectrophotometer in the wavelength range 800-3200 nm. Optical band gap of as-deposited and light exposed thin films was determined using Tauc’s plot. Optical band gap was found to be decreasing on light exposure upto 8 hours and after that no significant change was observed.(Ge2Sb2Te5)90Ag10 (GST-Ag) bulk alloy was prepared using melt quenching technique. GST-Ag thin film was deposited on glass substrate using thermal evaporation method. The prepared thin films were exposed to visible light (intensity of 105 Lux for 2, 8, 20 and 30 hours) using 25W LED lamp. Transmission spectra were taken using UV-vis-NIR spectrophotometer in the wavelength range 800-3200 nm. Optical band gap of as-deposited and light exposed thin films was determined using Tauc’s plot. Optical band gap was found to be decreasing on light exposure upto 8 hours and after that no significant change was observed.