Characterization of CdTe thin films fabricated by close spaced sublimation technique and a study of Cu doping by ion exchange process

CdTe thin films were prepared onto water-white glass substrates by the close spaced sublimation technique. The films annealed right after the deposition were then immersed in copper nitrate solution for different periods of time. These films were again annealed at 500 ^oC for 1 h to ensure the diffusion of copper in the films. The samples were characterized by X-ray diffraction and scanning electron microscopy. The electron microprobe analyzer showed an increase of copper-content in composition. The dc electrical conductivity showed a credible increase with increasing copper-content in the films. With the increase of copper-content, the hole mobility increased systematically. The optical parameters were deduced by fitting the optical transmittance in the wavelength range 300–2500 nm.     

Amorphous tungsten-doped In2O3 transparent conductive films deposited at room temperature from metallic target

Amorphous tungsten-doped In₂O₃ (IWO) films were deposited from a metallic target by dc magnetron sputtering at room temperature. Both oxygen partial pressure and sputtering power have significant effects on the electrical and optical properties of the films. The as-deposited IWO films with the optimum resistivity of 5.8 × 10^?4 Ω·cm and the average optical transmittance of 92.3% from 400 to 700 nm were obtained at a W content of 1 wt%. The average transmittance in the near infrared region (700–2500 nm) is 84.6–92.8% for amorphous IWO prepared under varied oxygen partial pressure. The mobility of the IWO films reaches its highest value of 30.3 cm² V^?1 s^?1 with the carrier concentration of 1.6 × 10²⁰ cm^?3, confirming their potential application as transparent conductive oxide films in various flexible devices.     

Optical and electrical properties of as-prepared and annealed (Se80Te20)100 − xAgx (0 ≤ x ≤ 4) ultra-thin films

Optical and electrical properties of the (Se₈₀Te₂₀)_100 ? xAg_x (0 ≤ x ≤ 4) ultra-thin films have been studied. The ultra-thin films were prepared by thermal evaporation of the bulk samples. Thin films were annealed below glass transition temperature (328 K) and in between glass transition temperature and crystallization temperature (343 K). Thin films annealed at 343 K showed crystallization peaks for Se–Te–Ag phases in the XRD spectra. The transmission and reflection of as-prepared and annealed ultra-thin films were obtained in the 300–1100 nm spectral region. The optical band gap has been calculated from the transmission and reflection data. The refractive index has been calculated by the measured reflection data. It has been found that the optical band gap increases, but the refractive index, extinction coefficient, real and imaginary dielectric constant decrease with increase in Ag content. The optical band gap and refractive index show the variation in their values with increase in the annealing temperature. The extinction coefficient increases with increasing annealing temperature. The surface morphology of ultra-thin films has been determined using a scanning electron microscope (SEM). The measured dc conductivity, under a vacuum of 10^? 5 mbar, showed thermally activated conduction with single activation energy in the measured temperature range (288–358 K) and it followed Meyer–Neldel rule. The dc activation energy decreases with increase in Ag content in pristine and annealed films. The results have been analyzed on the bases of thermal annealing effects in the chalcogenide thin films.     

Growth of pure ZnO thin films prepared by chemical spray pyrolysis on silicon

Structural, morphological, optical and electrical properties of ZnO thin films prepared by chemical spray pyrolysis from zinc acetate (Zn(CH₃COO)₂ 2H₂O) aqueous solutions, on polished Si(1 0 0), and fused silica substrates for optical characterization, have been studied in terms of deposition time and substrate temperature. The growth of the films present three regimes depending on the substrate temperature, with increasing, constant and decreasing growth rates at lower, middle, and higher-temperature ranges, respectively. Growth rate higher than 15 nm min⁻¹ can be achieved at T_s=543 K. ZnO film morphological and electrical properties have been related to these growth regimes. The films have been characterized by X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy.     

Electrical properties of a-Se85−xTe15Snx thin films

Se–Te alloys are an important system of chalcogenide glasses from application point of view. The incorporation of Sn additive alters the electrical properties of these alloys. The conductivity measurements have been done on the thin films of a-Se_85−xTe₁₅Sn_x (x = 0, 2, 4, 6 and 10 at.%) deposited using vacuum evaporation technique. Both dark (σ_d) and photoconductivity (σ_ph) show a maximum for x = 6 at.% of Sn, which, decreases on further Sn addition to the binary Se–Te alloy. The dark activation energy (ΔE_d) shows a minimum for x = 2 at.% of Sn, but increases on further Sn addition. There is a sharp decrease in photosensitivity (σ_ph/σ_d) on Sn addition to Se₈₅Te₁₅ alloy. The charge carrier concentration (n_σ) calculated with the help of dc conductivity measurements also show a maximum at x = 6 at.% of Sn. The results are explained on the basis of increase in the density of localized states present in the mobility gap on Sn incorporation.     

Amorphous to crystalline transition and optoelectronic properties of nanocrystalline indium tin oxide (ITO) films sputtered with high rf power at room temperature

ITO thin films were deposited on quartz substrates by the rf sputtering technique using various rf power keeping the substrates at room temperature. The influence of rf power on the structural, electrical, optical and morphological properties was studied by varying the rf power in the range 50–350 W. X-ray diffraction results show an amorphous – crystalline transition with nano grains. At a power of 250 W, the ITO film showed preferential orientation along (4 0 0) peak. It is observed from the optical transmission studies that the optical band gap increased from 3.57 to 3.69 eV when the rf power was increased from 50 to 250 W. The resistivity value is minimum and grain size is maximum for the ITO film deposited at 250 W. The X-ray photoelectron spectroscopy (XPS), Energy dispersive X-ray (EDX) and Atomic force microscopy AFM results confirm that the ITO films are stoichiometric and the surface contained nano-sized grains distributed uniformly all over the surface. It can be concluded that the ITO film deposited at room temperature with 250 W rf power, can provide the required optical and electrical properties useful for developing optoelectronic devices at lower temperatures.     

Optical characterization of sputtered amorphous aluminum nitride thin films by spectroscopic ellipsometry

We have measured and analyzed the optical constants and polarized optical properties of amorphous aluminum nitride (a-AlN) thin films deposited by RF reactive magnetron sputtering onto silicon(1 1 1) and glass substrates. The optical constants were obtained by analysis of the measured ellipsometric spectra in the wavelength range 300–1400 nm, using the Cauchy–Urbach model. Refractive indices and extinction coefficients of the films were determined to be in the range 1.80–2.11 and 8.6 × 10⁻³–1.5 × 10⁻⁵, respectively. Analysis of the absorption coefficient, in the wavelength range 200–1400 nm, shows the bandgap of a-AlN thin films to be 5.84 ± 0.05 eV. From the angle dependence of the p-polarized reflectivity we deduce a Brewster angle of 61° and a principal angle of 64°. Measurement of the polarized optical properties reveals a high transmissivity and very low absorptivity for a-AlN films in the visible and near infrared regions. X-ray diffraction analysis confirmed the amorphous nature of the films under study.     

Dielectric properties of bis(2,4 pentanedionato)copper(II) crystalline films grown on Si substrate for low-k applications

Bis(acetylacetonato)copper(II) thin films were prepared by sublimation at about 245 °C in vacuum on p-Si and glass substrates for dielectric and optical investigations. They were characterized by the X-ray diffraction (XRD) and energy-dispersion X-ray fluorescence (EDXRF) methods. The XRD pattern reveals that the prepared films were polycrystalline of monoclinic P2₁/n structure. The optical absorption spectrum of the prepared film was not identical to that of the molecular one, which identified by a strong absorption peak at 635 nm. The onset energy of the optical absorption of the complex was calculated by using Hamberg et al. method, which is usually used for common solid-state semiconductors and insulators. The dielectric properties for the complex as insulator were investigated on samples made in form of a metal-insulator-semiconductor (MIS) structure. The dielectric properties were studied in frequency range 1–1000 kHz and temperature range 298–333 K. The dielectric relaxation was analyzed in-terms of dielectric modulus M¹(ω). Generally, the present study shows that films of the complex grown on Si substrate are a promising candidate for low-k dielectric applications; it displays low-k value around 1.7 ± 0.1 at high frequencies.     

Correlation between the method of preparation and the properties of the sol–gel HfO2 thin films

This work describes the preparation of HfO₂ thin films by the sol–gel method, starting with different precursors such as hafnium ethoxide, hafnium 2,4-pentadionate and hafnium chloride. From the solution prepared as mentioned above, thin films on silicon wafer substrates have been realized by ‘dip-coating’ with a pulling out speed of 5 cm min^?1. The films densification was achieved by thermal treatment for 10 min at 100 °C and 30 min at 450 °C or 600 °C, with a heating rate of 1 °C min^?1. The structural and optical properties of the films are determined employing spectroellipsometric (SE) measurements in the visible range (0.4–0.7 μm), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The main objective of this paper was to establish a correlation between the method of preparation (precursor, annealing temperature) and the properties of the obtained films. The samples prepared from pentadionate and ethoxide precursors are homogenous and uniform in thickness. The samples prepared starting from chloride precursor are thicker and proved to be less uniform in thickness. Higher non-uniformity develops in multi-deposition films or in crystallized films. A nano-porosity is present in the quasi-amorphous films as well in the crystallized one. For the samples deposited on silicon wafer, the thermal treatment induced the formation of a SiO₂ layer at the coating–substrate interface.     

Characterization of europium doped lanthanum oxide films prepared by spray pyrolysis

In this work the characterization of europium doped lanthanum oxide films prepared by ultrasonic spray pyrolysis is reported. The films were prepared from lanthanum and europium nitrates over a corning glass substrate. The films structure was analyzed by X-ray diffraction, Microscopy Electronic and energy dispersive spectroscopy analysis. Photoluminescence and Raman scattering were performed. The excitation spectrum consists of the charge transfer peak at 280 nm and several lines in the 350–450 nm range corresponding to f–f transitions. The emission spectrum, excited at 280 nm, shows five peaks at 580, 595, 615, 652 and 698 nm, corresponding to the transitions of trivalent europium ion. The optical properties of films were compared with the one obtained from powders prepared by precipitation and heating of the precursor material.     

Low-temperature metal-induced crystallization of Mn-containing amorphous Ge thin films

This work focuses on the crystallization of amorphous germanium (a-Ge) thin films induced by manganese species. A series of Mn-containing a-Ge films ([Mn] ~ 0?3.7 at.% range) was deposited at 150 °C by the cosputtering technique. After deposition, all films were submitted to isochronal thermal annealing treatments up to 600 °C and analyzed by Raman scattering, optical transmission spectroscopy and electrical resistivity measurements. The experimental results indicate that: (a) Mn impurity lowers the crystallization temperature of a-Ge in ~ 100 °C, as confirmed by the Raman analyses, (b) the optical properties of the films are affected by both the insertion of Mn and the temperature of thermal treatment, with the optical bandgap staying in the range of ~ 0.7?1 eV, and (c) the electrical resistivity of the samples is also influenced by the Mn concentration and by the temperature of annealing, varying between ~ 1.0×10¹ and 1.6×10⁴ Ω cm. These experimental observations were systematically studied and the possible reasons associated to them are presented and discussed.     

InOx semiconductor films deposited on glass substrates for transparent electronics

Transparent undoped semiconductor indium oxide films were deposited by radio frequency (rf) plasma enhanced reactive thermal evaporation (rf-PERTE) of indium at low substrate temperature. It was experimentally verified that the variation of rf power density has a strong influence on the electrical and structural properties of the films. The thickness of the InO_x films is of about 100 nm. Results show that InO_x films show an average visible transmittance of about 85% and energy gap of about 2.6 eV. Structural and electrical conductivity measurements show that films are polycrystalline and there exists a linear variation of conductivity logarithm vs reciprocal of temperature. Electrical conductivity variation of 17.6 to 5.8 × 10⁻³ (Ω cm)⁻¹ for films produced at rf power densities ranging from 3.9 to 78.1 mW cm⁻³ was obtained. This controllable semiconductor behavior can therefore satisfy the requirement of a particular application for these type of films.     

Optical and structural proprieties of nc-Si:H prepared by argon diluted silane PECVD

Using argon as a diluent of Silane, hydrogenated amorphous and nanorocrystalline silicon films Si:H were prepared by radio-frequency (13.56 MHz) plasma enhanced chemical vapor deposition (rf-PECVD). The deposition rate and crystallinity varying with the deposition pressure and rf power, were systematically studied. Structural analysis (Raman scattering spectroscopy and X-ray diffraction), combined with optical measurements spectroscopy were used to characterize the films. The argon dilution of silane for all samples studied was 95% by volume, and the substrate temperature was 200 °C. The deposition pressure was varied from 400 mTorr to 1400 mTorr and varying rf power from 50 to 250 W. The structural evolution studies, shows that beyond 200 W of rf power, an amorphous-nanocrystalline transition was observed, with an increase in crystalline fraction by increasing rf power and working pressure. The films were grown at high deposition rates. The deposition rates of the films near the amorphous-nanocrystalline phase transition region were found in the range 6–10 Å/s. A correlation between structural and optical properties has been found and discussed.     

Transparent thin film transistors based on indium oxide semiconductor

Indium oxide films were deposited by radio-frequency plasma enhanced reactive thermal evaporation (rf-PERTE). The combined use of rf power and oxygen pressure allowed the control of the crystallite size in the film, changing the optical and electrical properties. The films obtained have electrical resistivity ranging from 13.7 to 1.7 × 10⁷ Ω cm. Transparent TFTs made with those films as semiconducting and conducting layers, respectively, present threshold voltages near 2 V and on/off ratios of 10⁴.     

Low temperature dielectric dispersion and electrical conductivity studies on Fe2O3 mixed lithium yttrium silicate glasses

Lithium yttrium silicate glasses mixed with different concentrations of Fe₂O₃ of the composition (40 ? x) Li₂O–10Y₂O₃–50SiO₂: x Fe₂O₃, with x = 0.3, 0.5, 0.8, 1.0, 1.2 and 1.5 (all in mol%) were synthesized. Electrical and dielectric properties including dielectric constant, ε′(ω), loss, tan δ, ac conductivity, σ_ac, impedance spectra as well as electric moduli, M(ω), over a wide continuous frequency range of 40 Hz to 10⁶ Hz and in the low temperature range 100 to 360 K were measured as a function of the concentration of Fe₂O₃. The dc conductivity is also evaluated in the temperature range 100 … 360 K. The temperature and frequency dispersions of dielectric constant as well as dielectric loss have been analyzed using space charge polarization model. The ac and dc conductivities have exhibited increasing trend with increasing Fe₂O₃ content beyond 0.5 mol%, whereas the activation energy for the conductivity demonstrated decreasing tendency in this dopant concentration range. Both quantum mechanical tunneling (QMT) and correlated barrier hopping models (CBH) were used for clarification of ac conductivity origin and the corresponding analysis has indicated that CBH model is more appropriate for this glass system. For the better understanding of relaxation dynamics of the electrical properties we have drawn the scaling plots for ac conductivity and also electric moduli. The plots indicated that the relaxation dynamics is independent on temperature but depends on concentration of Fe₂O₃. The dc conductivity is analyzed using small polaron hoping model. The increase of conductivity with the concentration of Fe₂O₃ beyond 0.5 mol% is explained in terms of variations in the redox ratio of iron ions in the glass network. The results were further analyzed quantitatively with the support of experimental data from IR, optical absorption and ESR spectral studies. The overall analysis has indicated that Li₂O–Y₂O₃–SiO₂ glasses containing more than 0.5 mol% of Fe₂O₃ are more suitable for achieving good electrical conductivity in these glasses.     

Electrical conductivity and dielectric relaxation in non-crystalline films of tungsten trioxide

Amorphous tungsten trioxide (a-WO₃) thin films were prepared by thermal evaporation technique. The electrical conductivity and dielectric properties of the prepared films have been investigated in the frequency range from 100 Hz to 100 kHz and in the temperature range 293–393 K. In spite of the absence of the dielectric loss peaks, application of the dielectric modulus formulism gives a simple method for evaluating the activation energy of the dielectric relaxation. The frequency dependence of σ(ω) follows the Jonscher’s universal dynamic law with the relation σ(ω) = σ_dc + Aω^s, where s is the frequency exponent. The conductivity in the direct regime, σ_dc, is described by the small polaron model. The electrical conductivity and dielectric properties show that Hunt’s model is well adapted to a-WO₃ films.     

Active planar waveguides based on sol–gel Er3+-doped SiO2–ZrO2 for photonic applications: Morphological,structural and optical properties

Er³⁺-doped glass-ceramic SiO₂–ZrO₂ optical planar waveguides were prepared by the sol–gel route using different SiO₂:ZrO₂ molar ratios (90:10, 85:15, 80:20 and 75:25). Multilayered films were deposited onto Si(1 0 0) substrates by the dip-coating technique. Structural characterization was performed using vibrational spectroscopy and X-ray diffraction. Some optical properties, densification and surface morphology of these films were investigated as a function of the SiO₂:ZrO₂ ratio, annealing temperature and time. Optical properties such as refractive index, number of propagating modes and attenuation coefficient were measured at 632.8, 543.5 and 1550 nm, by the prism coupling technique. Uniform surface morphology with roughness less than 0.5 nm. Low losses, less than 0.9 dB/cm at 612.8 nm in the TE₀ mode, were measured for the planar waveguides containing up to 25 mol% zirconium oxide. Luminescence of Er³⁺ in the near infrared was observed for the active nanocomposite.     

Space charge limited conduction in a-(Ge20Se80)1−xSnx thin films

The present paper reports the dc conductivity measurements at high electric fields in vacuum evaporated amorphous thin films of (Ge₂₀Se₈₀)_1−xSn_x glassy alloys where 0 < x < 1. Current–voltage (I–V) characteristics have been measured at various fixed temperatures. In these samples, at low electric fields, ohmic behavior is observed. However, at high electric fields (E ∼ 10⁴ V/cm), non-ohmic behavior is observed. An analysis of the experimental data confirms the presence of space charge limited conduction (SCLC) in the glassy materials studied in the present case. From the fitting of the data to the theory of SCLC, the density of defect states (DOS) near Fermi level is calculated. These results show that the effect of incorporation of Sn in the Ge–Se system is quite different at its low and high concentration. This peculiar role of third element Sn as an impurity in the pure binary Ge₂₀Se₈₀ glassy alloy is also discussed.     

Fabrication and characterization of transparent conductive ZnO:Al thin films prepared by direct current magnetron sputtering with highly conductive ZnO(ZnAl2O4) ceramic target

Using a highly conductive ZnO(ZnAl₂O₄) ceramic target, c-axis-oriented transparent conductive ZnO:Al₂O₃ (ZAO) thin films were prepared on glass sheet substrates by direct current planar magnetron sputtering. The structural, electrical and optical properties of the films (deposited at different temperatures and annealed at 400°C in vacuum) were characterized with several techniques. The experimental results show that the electrical resistivity of films deposited at 320°C is 2.67×10⁻⁴ Ω cm and can be further reduced to as low as 1.5×10⁻⁴ Ω cm by annealing at 400°C for 2 h in a vacuum pressure of 10⁻⁵ Torr. ZAO thin films deposited at room temperature have flaky crystallites with an average grain size of ∼100 nm; however those deposited at 320°C have tetrahedron grains with an average grain size of ∼150 nm. By increasing the deposition temperature or the post-deposition vacuum annealing, the carrier concentration of ZAO thin films increases, and the absorption edge in the transmission spectra shifts toward the shorter wavelength side (blue shift).     

Growth and characterization of nanostructured CdS/Polyaniline/CuInSe2 thin films for solar cell applications

In the present paper, we report about synthesis of nanostructured organic–inorganic heterojunction of CdS/Polyaniline/CuInSe₂ thin films by cost effective chemical route at room temperature, for solar cell application. As such obtained thin films are characterized for structural, compositional, morphological, optical and electrical properties by X-ray diffraction (XRD) pattern, energy dispersive X-ray (EDAX) analysis, scanning electron microscopy (SEM), optical absorbance spectra and I–V response respectively. The XRD reveals the polycrystalline nature of the thin films having tetragonal crystal structure and a crystallite size of 19 nm. The presence of observed and expected elements in the EDAX spectra confirms the elemental compositions in CdS/Polyaniline/CuInSe₂ thin films. From SEM images it can be inferred that the surface morphology of the Polyaniline thin films exists like clothing fibers, while CdS/CuInSe₂ shows granular shape particles distributed over the substrate and the SEM of CdS/Polyaniline/CuInSe₂ represents mixing and attachment of circular particles to fiber like structure. The optical absorbance spectra have shown red shift in absorbance strength and energy band gap value of CdS/CuInSe₂ from ~ 1.36 eV to ~ 1.62 eV upon formation of CdS/Polyaniline/CuInSe₂ thin film. The I–V response of CdS/CuInSe₂ and CdS/Polyaniline/CuInSe₂ measured under dark and illumination to 100 mW/cm² light, exhibited the solar characteristics from these graphs and the conversion efficiency calculated is observed to be 0.26 and 0.55% for CdS/CuInSe₂ and CdS/Polyaniline/CuInSe₂ thin films respectively.