In situ electrical conductivity and amorphous-crystalline transition in vacuum-deposited thin films of Se20Te80 alloy

In situ electrical conductivity measurements have been carried out on vacuum-deposited thin films of Se₂₀Te₈₀ alloy during heating and cooling cycles. The electrical conductivity and X-ray diffraction studies show that the as-grown Se₂₀Te₈₀ films are amorphous and, upon heating, undergo an irreversible amorphous-crystalline transition between 315 and 350 K. The observation that the as-grown thin films (deposited at room temperature on glass substrates) are amorphous is in contrast to earlier observations by other workers who find that they are polycrystalline. Above the transition temperature, the electrical conductivity of the polycrystalline Se₂₀Te₈₀ films changes as an exponential function of reciprocal temperature. The amorphous-crystalline transition in Se₂₀Te₈₀ thin films is broad, with films of high initial resistance having lower transition temperatures and low-resistance films having higher transition temperatures. The observation of a broad transition in the case of the present Se₂₀Te₈₀ thin films has to be contrasted with our earlier observations of sharp transitions in the case of Se₈₀Te₂₀ and Se₅₀Te₅₀ thin films.     

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 .     

The electrical conductivity of copper and tin thin films vacuum deposited in a lateral electric field

Copper and tin thin films of different thicknesses in the coalescence thickness range (160, 210 and 260 Å) were grown by vacuum deposition onto clean glass substrates at room temperature under a pressure of 2 × 10^?5 Torr in different electric fields between 0 and 200 V cm^-1 aligned parallel to the substrates. The electrical conductivities of the films were measured immediately after formation both in situ and after letting air into the system.We found that the application of an electric field of less than 60 V cm^-1 decreased the resistance of the films. However, the application of stronger electric fields produced an increase in the film resistance. This is attributed to a disturbance of the electrostatic forces between the growing islands by the redistribution of charges in the presence of the applied electric field which causes an increased rate of coalescence of the islands in the film.     

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.     

On morphological, structural and electrical properties of vacuum deposited pentacene thin films

Films of different thickness (50, 100, 150 and 200 nm) were deposited by thermal evaporation in vacuum on two types of substrates glass and ITO. The deposition was performed under a pressure of 10⁻⁶ mB with a rate of 0.25 nm/s. Films surface investigations showed morphological and structural changes in function of films thickness and the nature of the substrate. Films optical transmission was analysed in the 280-1600 nm spectral range and the electrical measurements were done in low vacuum (10⁻¹:10⁻² mB) and in dark.     

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.     

The electrical properties of vacuum deposited tellurium films

A study has been made of the electrical properties of tellurium films deposited onto two different substrate materials, 7059 alkali free glass and single crystal potassium bromide. The films were always p-type with crystallographic defects resulting in the formation of additional acceptor centres. The carrier mobility was found to be dependent on temperature through an equation of the form $\text{μ}{}_{\mathrm{<mtext>H</mtext>}}\text{= μ}{}_0\text{exp}\text{(}\text{?E}\text{kT)}$, which is typical of polycrystalline films, where the effects of grain boundaries predominate. The value of μ₀ was found to vary linearly with crystallite size for specimens with a comparable carrier concentration. Crystalline defects, within the grains, were also found to be significant in determining the value of the carrier mobility. At no time was there any evidence to suggest that surface scattering was significant in tellurium films.     

Transport properties of vacuum deposited tin-tellurium alloy films

The transport properties of Sn_1?xTe_x (0相似文献   

Fabrication and characterization of vacuum deposited fluorescein thin films

Simple vacuum evaporation technique for deposition of dyes on various solid surfaces has been developed. The method is compatible with conventional solvent-free nanofabrication processing enabling fabrication of nanoscale optoelectronic devices. Thin films of fluorescein were deposited on glass, fluorine-tin-oxide (FTO) coated glass with and without atomically layer deposited (ALD) nanocrystalline 20 nm thick anatase TiO₂ coating. Surface topology, absorption and emission spectra of the films depend on their thickness and the material of supporting substrate. On a smooth glass surface the dye initially forms islands before merging into a uniform layer after 5 to 10 monolayers. On FTO covered glass the absorption spectra are similar to fluorescein solution in ethanol. Absorption spectra on ALD-TiO₂ is red shifted compared to the film deposited on bare FTO. The corresponding emission spectra at λ = 458 nm excitation show various thickness and substrate dependent features, while the emission of films deposited on TiO₂ is quenched due to the effective electron transfer to the semiconductor conduction band.     

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.     

Studies on the photoconductivity of vacuum deposited ZnTe thin films

The present paper reports the analysis of photoconductivity of vacuum deposited zinc telluride (ZnTe) thin films as a function of substrate temperature and post-deposition annealing. Detailed analyses were first carried out to understand the effect of substrate temperature and annealing on the structure, composition, optical and electrical properties of the films. The films deposited at elevated substrate temperatures showed faster and improved photoresponse. Post-deposition annealing was found to further enhance the photoresponse of the films. Attempts have been made to explain the improvement in the photoresponse on the basis of structural and compositional changes, taking place in the films, due to the substrate temperature and annealing.     

Impact of thickness on vacuum deposited PbSe thin films

Lead Selenide thin films were prepared by vacuum evaporation technique with different thickness ranges from 50 to 200 nm on glass substrates. The structural studies revealed that the prepared films are strongly oriented on (2 0 0) plane with rock-salt crystal structure. The various structural parameters such as grain size (D), lattice constant (a), micro strain (ε) and dislocation density (δ) were calculated. The surface morphology of the films was also analyzed. The optical absorption of the films starts with visible region and obtained energy gap of the films lies between 1.5 and 1.9 eV. The room temperature Photoluminescence spectrum shows the emission peak at visible region (380-405 nm) and the blue shift was observed with decreasing the film thickness. The electrical mobility, resistivity, carrier concentration and mean free path (L) of the free carriers of the films were studied for all the samples and compared.