In situ electrical conductivity and the amorphous-crystalline transition in vacuum deposited thin films of Se80Te20 alloy

The electrical conductivity of thin films of Se₈₀Te₂₀ polycrystalline alloy vacuum-deposited at room temperature on glass substrates has been studied duringin situ heating and cooling cycles. From the electron diffraction of as-grown films it is seen that the studied films are amorphous at room temperature. The electrical conductivity and electron diffraction studies showed that the as-grown amorphous thin films undergo an amorphous-crystalline transition in the temperature range 340 to 360 K. Upon cooling, the films appear to undergo a crystalline crystalline transition around the same temperatures. There does not appear to be any dependence of the amorphous-crystalline transition temperature on the thickness of the films. However, high-resistance films (thinner films) have a well-defined transition temperature while the low-resistance films (thicker films) have a broader transition. The electrical conductivity of polycrystalline Se₈₀Te₂₀ films above 360 K appears to be an exponential function of reciprocal temperature.     

Electrical conductivity and thermoelectric power of amorphous Sb2Te3 thin films and amorphous-crystalline transition

The results of electrical conductivity and thermoelectric studies on antimony telluride, a promising thermoelectric material, in the thin film state are reported. Films were vacuum-deposited on to clean glass substrates with thickness between 50 and 200 nm and studied in the temperature interval 300 to 470 K. On heating the as-grown films, there is a sharp fall both in the Seebeck coefficient and the electrical resistivity at around 340 to 370 K for all the films. This is attributed to an amorphous to crystalline transition, which is confirmed by X-ray diffractogram and electron diffraction patterns.[/p]     

Optical constants and electrical conductivity of Ge20Se60Sb20 thin films

Optical absorption and electrical resistivity of amorphous Ge₂₀Se₆₀Sb₂₀ films are investigated as a function of the thermal annealing. The dependence of the optical absorption coefficient on the photon energy is ascribed by the relation (h) = B(h–E_o)². Increasing the annealing temperature from 423 K to 553 K, decreases the optical gap of the film from 1.25 eV to 0.78 eV. The effect of annealing temperature on high frequency dielectric constant () and carrier concentration (N) was also studied. As a result of annealing the film at 533 K, the electrical resistivity and activation energy for conduction decreased from 5.7 × 10⁷ to 2.9 × 10² ·cm and from 0.94 to 0.34 eV, respectively. The crystalline structures resulting from heat treatment at different elevated temperatures have been studied by X-ray Diffraction (XRD). The optical and electrical changes were attributed to the amorphous-crystalline transformations in the chalcogenide films.     

Effect of In additive on the photosensitivity of glassy Se80Te20 alloy

Photo-electrical measurements are done on thin films of Se_80?x Te₂₀In _x (0 ≤ x ≤ 20) to see the effect of In on the photoconductive properties of binary Se₈₀Te₂₀ alloy. The photosensitivity (σ_ph/σ_d) and activation energy of photoconduction (ΔE _ph) are determined for this purpose. It has been found that σ_ph/σ_d and ΔE _ph are decreased with increasing concentration of the third element. The results are explained in terms of the increase in density of the defect states with the increase in concentration of the additive in thin films of Se_80?x Te₂₀In _x .     

Electrical properties of Bi80Sb20 alloy thin films,vacuum-deposited at different substrate temperatures

Bismuth antimonide (composition 8020) alloy thin films have been prepared by vacuum deposition at different substrate temperatures and, after annealing, their resistances have been recorded as a function of temperature, between 77 K and 500 K. The observed resistance against temperature behaviour of the films, and the effect of thickness and substrate temperature during deposition of the films, has been explained by considering that these films behave as semiconductors; the overlap between valence and conduction bands being removed due to the presence of antimony, the influence of a quantum size effect and the fact that the grain size of the films formed is a function of thickness and substrate temperature.     

Electrical conductivity,defect density and structure of obliquely vacuum-deposited tin antimonide alloy thin films

Thin films of tin antimonide alloy have been vacuum deposited on glass substrates at room temperature at different angles of deposition. These films have been heat-treated in situ and their electrical resistance has been continuously monitored during the heating-cooling cycle. From the resistance against temperature data during heat-treatment, initial lattice distortion energy spectra of these films have been determined using Vand's theory. It has been found that for angles of deposition below 50°, the defect density increases with increasing angle of deposition. At higher angles of deposition, the resistance against temperature behaviour during heat-treatment is different. This is attributed to the columnar structure of the film. It is also found that preferential decay energies of the defects exist and these are 1.45 and 1.80 eV.     

Estimation of Mott parameters in amorphous Se80Te20 and Se80Te10M10 (Cd,In, Sb) alloys

In the present communication, d.c. conductivity of a-Se₈₀Te₂₀ and a-Se₈₀Te₁₀M₁₀ (M = Cd, In, Sb) alloys has been studied in the temperature range 225–311 K in order to identify the conduction mechanism and to analyze the effect of different metallic additives on d.c. conduction in a-Se₈₀Te₂₀ alloy below the room temperature. An analysis of the experimental data confirms that conduction in low temperature region is due to variable range hopping in localized states near the Fermi level. The Mott parameters have been calculated in a-Se₈₀Te₂₀ and a-Se₈₀Te₁₀M₁₀ (M = Cd, In, Sb) alloys. The experimental data is found to fit well with Mott condition of variable range hopping conduction.     

Growth and electrical transport properties of In2Te3 thin films

Hall coefficient and d.c. conductivity studies in the temperature range 100–625 K were made on polycrystalline In₂Te₃ films grown on glass and mica substrates. When the films were cycled above about 525 K the conductivity was found to be irreversible; this is explained in terms of structural changes at high temperature. It was found that the Hall mobilities of the films are independent of temperature, showing the predominance of neutral impurity scattering over again boundary scattering.     

Optical study of ion-induced effects in Ge20Se80−xBix thin films

Incorporation of impurities into the semiconductors by high energy heavy ions is a non-equilibrium process, which can result in intriguing near surface or subsurface property changes depending upon the energy of the ion. Present work deals with the optical study of Ni ion irradiated Ge₂₀Se_80−xBi_x thin films samples. The thin film samples were deposited by the flash evaporation method at 10⁻⁵ Torr and were characterized by XRD, XRF, EPMA and DSC. Irradiation was done on samples with a Ni ion beam of 75 MeV energy. The optical spectra of the films were recorded and the optical band gap study was done both as a function of dose (5 × 10¹² to 10¹⁴ ions/cm²) as well as composition of the samples. The optical band gap was found to decrease with increasing Bi content as well as with increasing dose.     

Related structural,electrical and photoelectrical properties of vacuum-deposited GaP thin films

GaP thin films with thicknesses from 0.1 to 0.6 μm were prepared by the thermal evaporation of the compound GaP onto quartz substrates at temperatures from ambient temperature to 740 °C. The properties of the films depended strongly on substrate temperature and deposition rate. With increasing substrate temperature the film structure changed from amorphous to textured polycrystalline with a strong [100] texture. The temperature of the amorphous-to-crystalline transition depended on deposition rate and was found to be 360 and 400 °C for deposition rates of 2 and 10 Å s^-1 respectively. At these temperatures the electrical resistivity of the films fell sharply from 10⁸ Ω cm to a minimum value of $\text{5 × 10}{}^4\text{Ω}\text{cm}$, after which it increased again with increasing temperature. The amorphous films exhibited a moderate photosensitivity with a maximum value near the temperature of the structural transition; above this temperature the films lost their photosensitivity completely. The spectral dependence of the photoconductivity was measured and an attempt was made to interpret the observed spectra.     

Optical properties of evaporated Ge20Se80−x Tl x thin films

Chalcogenide glasses with composition Ge₂₀Se_80–x Tl _x (x=10, 15, 20, 25, 35%) have been prepared by the usual melt-quenching technique. Thin films of the mentioned compositions have been prepared by the electron beam evaporation. In addition, another set taken from the composition ofX=30 at % with different thicknesses (d=14.7, 30.0, 56.5, 70.0, 101.0, 180.0 nm) have been taken into consideration. The X-ray diffraction (XRD) analysis revealed the amorphous nature of the prepared films. It was found that, in contrast to the optical gap (E _op), both the extent of the band tailing (B), and the band gap (E _e) increase with increasing thallium content. In other side,E _op showed thickness independency. The refractive index (n) showed obvious dependence on both composition and thickness also on the energy of the incident radiation.     

Optical properties of Bi2Te2Se thin films

Some optical parameters of Bi₂Te₂Se thin films, determined from the measured absorbance and transmittance at normal incidence in the visible spectral range, were studied as functions of film thickness and annealing temperature. These parameters were found to be sensitive to both film thickness and microstructure change caused by annealing in a film. The effect of thickness and temperature of annealing on the optical gap was interpreted in terms of elimination of defects and change of disordering in the amorphous matrix.     

The electrical conductivity in thin polycrystalline p-terphenyl films

The electrical conductivity of thin polycrystalline p-terphenyl films was investigated as a function of electric field, temperature and film thickness. The experimental data may be interpreted in terms of a hopping process between localized sites through a potential barrier lowered by the electric field according to the modified Poole-Frenkel equation.     

Ultrasonic velocities and thermal expansion coefficients of amorphous Se80Te20 and Se90Te10 alloys near glass transitions

Precise measurements of the ultrasonic velocities and thermal expansivities of amorphous Se₈₀Te₂₀ and Se₉₀Te₁₀ alloys are reported near the glass transition. The samples are produced by liquid quenching. The longitudinal and transverse velocities are measured at 10 MHz frequency using the McSkimin pulse superposition technique. The thermal expansivities,, are measured using a three-terminal capacitance bridge. The-values show a sharp maximum near the glass transition temperature,T _g. The ultrasonic velocities also show a large temperature derivative, dV/dT nearT _g. The data are discussed in terms of existing theories of the glass transition. The continuous change in shows that the glass transition is not a first-order transition, as suggested by some theories. The samples are found to be deformed by small loads nearT _g. The ultrasonic velocities and dV/dT have contributions arising from this deformation.     

The electrical conductivity of inhomogeneous thin metallic films

This paper reports the following results: (i) an explicit for the electrical conductivity of a thin metal film where the electron mean free path is not constant through its thickness, and (ii) calculations showing how in this case an illusory fit to the Fuchs-Sondheimer result can be obtained with a dependence of the specularity parameter on thickness or angle. A survey of experimental results is also presented.