[en] Thin films of Sn₁₀Sb₂₀Se_70-XTe_X (0 ≤ X ≤ 14) composition were deposited using thermal evaporation technique. As-prepared films were amorphous as studied by X-ray diffraction. Surface morphology studies revealed that films have surface roughness ∼ 2 nm and av. grain size ∼ 30 nm. Optical band gap E_g showed a sharp decrease for initial substitution of Se with Te upto 2 at.%. A broad hump in the optical band gap is observed for further substitution of Se with Te. The trend of optical band gap variation with tellurium content has been qualitatively explained using band model given by Kastner. The dc-conductivity measurements showed thermally activated conduction with single activation energy for the measured temperature regime and followed Meyer–Neldel rule. The dc-activation energy has nearly half the value as that of optical band gap that revealed the intrinsic nature of semiconductor. The annealing below glass transition T_g led to decrease in optical band gap as well as dc-activation energy that might be related to increase of disorder in material with annealing.

[en] Polycarbonates like CR-39, SR-86 and Makrofol have been irradiated with ¹²C⁵⁺ ions of energy 5.0 MeV/u and fluences of 10¹¹, 10¹² and 10¹³ ions/cm². The optical studies show an increase in absorption in the shorter wavelength region (250-500 nm) which is more pronounced in SR-86. The study also reveals that the increase in radiation dose extends the optical absorption region to longer wavelengths. The annealing of radiation damaged polymer samples at 120 deg. C for 75 min partially recovers the damage. It is observed that the bulk etch rates of these polymers increase after irradiation

[en] Thin films of GeTe-rich pseudobinary compound, Ge₈Sb₂Te₁₁, have been synthesized from its polycrystalline bulk by thermal evaporation. Amorphous nature of thermally evaporated films has been confirmed by X-ray diffraction study. The temperature dependent electrical, optical and structural properties are presented. For films annealed at 190 °C, a large change in electrical and phase transition temperature was observed, with almost no change in optical properties. The phase transition temperature of Ge₈Sb₂Te₁₁ was ∼ 205 °C and decreases appreciably for the post deposition films annealed at 190 °C. The films morphology and their chemical composition have been studied using Scanning electron microscopy linked with energy dispersive X-ray spectrometer. - Highlights: ► Phase change materials GeTe-rich pseudobinary compound (Ge₈Sb₂Te₁₁). ► Thermal evaporation of thin films from polycrystalline Ge₈Sb₂Te₁₁ bulk. ► Temperature dependent structural, electrical and optical properties are presented. ► The optical contrast is more than 30%

[en] Photodoping of Ag into amorphous Ge₂Sb₂Te₅ thin films has been carried out by illuminating thermally evaporated Ge–Sb–Te:Ag bilayers with a halogen lamp in the inert atmosphere at room temperature. Amorphous nature of the as-deposited and photodoped films was confirmed by an X-ray diffraction study. The composition of Ge₂Sb₂Te₅ thin films and the amount of Ag photodiffused have been gathered from electron probe micro-analyzer having a wavelength dispersive spectrometer. Amorphous-to-crystalline transition of the films was induced by thermal annealing and the structural phases were identified by X-ray diffraction. The crystalline temperature of the films was evaluated by temperature dependent sheet resistance measurements. The effects of photodoped Ag concentration on the optical properties of the Ge₂Sb₂Te₅ films have been examined by transmission and reflection spectrometry. It was found that the optical band gap, the sheet resistance and the phase transition temperature increase while the absorption coefficient and extinction coefficient decrease upon incorporation of Ag in Ge₂Sb₂Te₅ system. A correlation between the optical band gap and the electronegativity of the alloys indicates that the optical band gap increases with the decrease of electronegativity. - Highlights: • Carried out photodiffusion of Ag into Ge-Sb-Te amorphous films. • The at.% of photodoped Ag content increases with the thickness of Ag film. • Structural and optical properties of Ag photodoped GST films are studied. • Optical band gap increases with decrease of electronegativity of photodoped films

[en] Amorphous thin films of Se_80-xTe₂₀Pb_x (0< x<2) have been prepared by thermal evaporation method. The effect of 40 MeV ²⁸Si⁵⁺ ion irradiation on the optical band gap (E_g) has been investigated. Blue shift in the optical band gap of Se_80-xTe₂₀Pb_x (0< x<2) has been observed upon irradiation with heavy ions. The E_g of Se_80-xTe₂₀Pb_x (x=1.4) increases from 1.36 to 1.48 eV with the increase in the irradiation fluence from 10¹² to 5 x 10¹³ ions/cm², respectively. All the other samples also show similar behavior. Results have been explained, considering strong electron-lattice coupling and some changes in the defects configurations upon irradiation with heavy ions, resulting in an increase of the optical band gap

[en] Bulk amorphous samples of Te-substituted Sn₁₀Sb₂₀Se_70-X Te_X (0 ≤X ≤12) were prepared using a melt quenching technique. Calorimetric studies of the samples were performed using differential scanning calorimetry (DSC) and the glass transition temperature and crystallization temperature were evaluated from DSC scans. The glass transition temperature T_g exhibits a sharp decrease for small Te substitution of X=2, thereafter increases with increase in Te content up to X=10, and then decreases for further Te substitution. The apparent activation energy for glass transition and the activation energy for crystallization were calculated using Kissinger, modified Kissinger, and Matusita equations. The change in glass transition temperature T_g has been explained based on the bond formation energy of different heteropolar bonds. The optical band gap of thermally evaporated thin films of Sn₁₀Sb₂₀Se_70-X Te_X (0 ≤X ≤12) was calculated from reflectance and transmittance data. The optical band gap variation with tellurium content exhibits a sharp decrease for an initial tellurium substitution of X=2 similar to that of the glass transition temperature and thereafter a peak is observed in optical band gap around X=4 composition. (orig.)

[en] This paper reports the influence of silver (Ag) addition on the optical constants of chalcogenide (Se₈₀Te₂₀)_100-xAg_x (0 ≤ x ≤ 4) thin films. Films of (Se₈₀Te₂₀)_100-xAg_x (0 ≤ x ≤ 4) glasses were prepared by thermal evaporation of the bulk samples. The transmittance and reflection spectra of amorphous thin films were obtained in the spectral region in the range 400-2500 nm. The optical band gap and the absorption coefficient were calculated from the transmission and reflection data. Swanepoel method has been applied to derive the real and imaginary parts of the complex index of refraction, refractive index, and also the thickness of amorphous films. The dispersion parameters are calculated by using the Wemple-DiDomenico model. The optical constants, i.e., the refractive index, extinction coefficient, absorption coefficient, and optical band gap are determined and their compositional dependence is considered. The results are discussed on the basis of defects and disorders present in chalcogenide systems. (copyright 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

[en] Amorphous thin films were prepared from the bulk composition of Ge₂₂Sb₂₂Te₅₆(GST) alloy by thermal evaporation in good vacuum condition. The amorphous nature of as-deposited films was checked with x-ray diffraction (XRD) studies. X-ray photoelectron spectroscopy (XPS) has been used to determine the binding energies of the core electrons in amorphous thin GST films. In XPS, we performed the survey scan from the binding energy (BE) range from 0-1100 eV and core level spectra of Ge 3d, Sb 3d and Te 3d.

[en] The effects of phase separation on the structure and photoconductivity kinetics in Sn_xSb₂₀Se_80-x (x = 10,11,12.5) glassy films have been studied. Crystalline peaks for SnSe₂, Sn₂Sb₄Se₈ and Sn₄Sb₄Se₁₀ phases are found in x = 12.5 films, while Sb₂Se₃ is the other major phase revealed from x-ray diffraction studies. The optical gap remains constant at 1.55 eV for x = 10,11 samples and then decreases to 1.50 eV for the x = 12.5 film, while a blueshift in reflectivity maxima (R_max) has been observed with Sn content. An increase in room temperature conductivity and a decrease in dc activation energy with Sn content have been observed. Bimolecular recombination is the dominant recombination process under steady state illumination for all of the samples. Decay of photocurrent (after cessation of light) fits well to a stretched exponential function; the decay time constant and dispersion parameter have been discussed. The growth of network connectivity with an increase in compositional/configurational disorder induces states in the mobility gap and affects the structure of band tails. These results have been interpreted in the light of the barrier cluster model developed for chalcogenide glasses.

[en] The effect of substrate temperature and deposition rate on the structural, electrical and optical properties of vacuum evaporated CdSe films of thickness 0.2 μm to 0.5 μm is reported. The electron micrograph patterns show that the grain size increases with increase in substrate temperature. The resistivity of films vary from 10sup(-1) ohm cm for room temperature substrate films to 10sup(8) ohm cm for films deposited at 250deg C substrate temperature. From the analysis of the transmission data it is found that the absorption edge becomes sharper besides shift in band gap approaching single crystal value, with the increase in substrate temperature. Good photoconducting properties are exhibited in films deposited at higher substrate temperature and high deposition rates. (auth.)