Structural characterization and optical properties of Cd(1−x)MnxSe thin films

Stoichiometric bulk ingot materials of the ternary mixture Cd_(1−x)Mn_xSe (0.05 ≤ x ≤ 0.9) were prepared by direct fusion of the constituent elements in vacuum sealed silica tubes. X-ray diffraction studies indicate that the investigated samples exhibited a hexagonal structure. The lattice parameters varied linearly with Mn content, following Vegard's law. Thin films were deposited by thermal evaporation from the pre-synthesized ingot material, onto glass substrates. X-ray and electron diffraction studies on the as-deposited and annealed films revealed an amorphous-to-crystalline phase transition at T_a ≈ 423 K. EDAX studies on the prepared films show that the as-deposited films are nearly stoichiometric. The transmittance and reflectance of the deposited Cd_(1−x)Mn_xSe films were measured at normal light incident in the wavelength spectral range 500-2500 nm. Analysis of the transmittance spectra in the entire wavelength range allowed the determination of the refractive index. The dispersion parameters have been calculated, from which the static refractive index as well as static dielecric constant were calculated. Analysis of the absorption coefficient of the investigated films revealed the existence of both the allowed direct and forbidden direct optical transition mechanisms. The corresponding energies were estimated.     

Influence of substrate temperature on structural,optical, and electrical properties of flash evaporated CuIn0.81Al0.19Se2 thin films

Chalcopyrite copper indium aluminum diselenide (CuIn_0.81Al_0.19Se₂) compound is prepared by direct reaction of high purity elemental copper, indium, aluminum and selenium in their stoichiometric proportion. Structural and compositional characterizations of pulverized material confirm the formation of a single phase, polycrystalline nature. CuInAlSe₂ (CIAS) thin films are deposited on organically cleaned soda lime glass substrates using flash evaporation technique by varying the substrate temperatures in the range from 423 K to 573 K. Influence of substrate temperature observed by X-ray diffraction (XRD), scanning electron microscope (SEM), optical and electrical measurement. CIAS Films grown at different substrate temperatures are polycrystalline in nature, exhibiting a chalcopyrite structure with lattice parameters a = ∼0.576 nm and c = ∼1.151 nm. The crystallinity in the films increases with increasing substrate temperature up to 473 K, and tend to degrade at higher substrate temperatures. Optical band gap is in the range of 1.20 eV–1.38 eV and the absorption coefficient is close to 10⁵ cm⁻¹. Electrical characterization reveals p-type conductivity and the structural, morphological and optical properties indicate potential use of CIAS thin films as an absorber layer for thin film solar cell applications.     

CuIn1 − xAlxSe2 thin films obtained by selenization of evaporated metallic precursor layers

CuIn_1 − xAl_xSe₂ (CIAS) thin films were grown by a two stage process. Cu, In and Al layers were sequentially evaporated and subsequently heated with elemental selenium in a quasi-closed graphite box. Different x values (0 ≤ x ≤ 0.6) were obtained by varying the Al and In precursor layers thicknesses. Selenization conditions such as Se amount provided during the selenization process were adjusted in order to optimize the film properties. Polycrystalline CuIn_1 − xAl_xSe₂ thin films with chalcopyrite structure were obtained. Referred to CuInSe₂ thin films the lattice parameters, the (112) orientation and the average crystallite size decreased and the band gap energy increased with increasing Al content. To optimize structural properties of the CIAS films a higher Se amount was required as the x value increased. The incorporation of Al changed the thin film morphology towards smaller grain sizes and less compact structures.     

Structural and optical properties of Cd x Zn(1 − x)Te thin films

Seven Cd _x Zn_{(1 ? x} Te solid solutions with x = 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 and 1.0 were synthesized by fusing stoichiometric amounts of CdTe and ZnTe constituents in silica tubes. Each composition was used in the preparation of a group of thin films of different thicknesses. Structural investigation of the obtained films indicates they have a polycrystalline structure with predominant diffraction lines corresponding to (111) (220) and (311) reflecting planes, which can be attributed to the characteristics of growth with the (111) plane. The optical constants (the refractive index n, the absorption index k, and the absorption coefficient α) of Cd _x Zn_{(1 \s -x)} Te thin films were determined in the spectral range 500–2000 nm. At certain wavelengths it was found that the refractive index, n, increases with increasing molar fraction, x. It was also found that plots of α² (hv) and α^1/2 (hv) yield straight lines, corresponding to direct and indirect allowed transitions respectively obeying the following two equations: $$\begin{gathered} E_g^d = 1.583 + 0.277x + 0.197x^2 \hfill \\ E_g^{ind} = 1.281 + 0.111x + 0.302x^2 \hfill \\ \end{gathered}$$      

Formation and properties of AgInSe2 thin films by co-evaporation

The electrical and optical properties of silver indium selenide thin films prepared by co-evaporation have been studied. X-ray diffraction indicates that the as prepared films were polycrystalline in nature. The lattice parameters were calculated to be a=0.6137 and b=1.1816 nm. Composition was determined from energy dispersive analysis of X-ray. Silver indium selenide thin films were also prepared by bulk evaporation of powdered sample for comparative study. They have an optical band gap (E_g) of 1.25 eV and it is a direct allowed transition. Refractive index (n) and extinction coefficient (k) were calculated from absorption and reflection spectra. Steady-state photoconductivity was measured from 300 to 400 K. Carrier lifetime was calculated from transient photoconductivity measurements at room temperature at different intensities of illumination.     

Microstructure and electrical properties of Ba0.7Sr0.3(Ti1 − xZrx)O3 thin films prepared on copper foils with sol-gel method

Ba_0.7Sr_0.3(Ti_1 − xZr_x)O₃ (x = 0, 0.1, 0.2) (BSZT) thin films have been prepared on copper foils using sol-gel method. The films were annealed in an atmosphere with low oxygen pressure so that the substrate oxidation was avoided and the formation of the perovskite phase was allowed. The X-ray diffraction results show a stable polycrystalline perovskite phase, with the diffraction peaks of the BSZT films shifting toward the smaller 2θ with increasing Zr content. Scanning electron microscopy images show that the grain size of the BSZT thin films decreases with increasing Zr content. High resolution transmission electron microscopy shows the clear lattice and domain structure in the film. The dielectric peaks of the BSZT thin films broaden with increasing Zr content. Leakage current density of Ba_0.7Sr_0.3(Ti_1 − xZr_x)O₃ (x = 0.1) thin film is the lowest over the whole applied voltage.     

Effect of SbSn additions on the physical characterization of amorphous Se

Different compositions of Se_100−x(SbSn)_x (0 ≤ x ≤ 14 at.%) glasses were prepared by the well-known melt quench technique. Thin films of these glasses were prepared by thermal evaporation onto ultrasonic cleaned glass substrate. Transmittance spectra of these films were measured in the wavelength range 400–2500 nm by using Jasco double beam spectrophotometer. A straight forward analysis proposed by Swanepoel, based on the maxima and minima of the transmittance spectra, allows to accurate determination of the film thickness and the complex index of refraction. Increasing SbSn content at the expense of Se atoms is found to affect the refractive index and the extinction coefficient of these films. The refractive indexes were discussed in terms of the single-oscillator Wemple–DiDomenico model. The compositional dependence of the optical band gap for the Se_100−x(SbSn)_x (0 ≤ x ≤ 14 at.%) thin films is discussed in terms of the chemical-bond approach.     

Characterization of nanostructured photosensitive (NiS)x(CdS)(1−x) composite thin films grown by successive ionic layer adsorption and reaction (SILAR) route

Recently ternary semiconductor nanostructured composite materials have attracted the interest of researchers because of their photovoltaic applications. Thin films of (NiS)_x(CdS)_(1−x) with variable composition (x = 1-0) had been deposited onto glass substrates by the successive ionic layer adsorption and reaction (SILAR) method. As grown and annealed films were characterised by X-ray diffraction, scanning electron microscopy and EDAX to investigate structural and morphological properties. The (NiS)_x(CdS)_(1−x) films were polycrystalline in nature having mixed phase of rhombohedral and hexagonal crystal structure due to NiS and CdS respectively. The optical and electrical properties of (NiS)_x(CdS)_(1−x) thin films were studied to determine compsition dependent bandgap, activation energy and photconductivity. The bandgap and activation energy of annealed (NiS)_x(CdS)_(1−x) film decrease with improvement in photosensitive nature.     

Compositional effect on optical characteristics of solution grown (Cd<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Sn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)S thin films

A good deal of information regarding the synthesis and optical properties of chemically grown (Cd_1?x Sn _x )S (x = 0.01–0.40) thin film has been reported. The growth of these films depends on various preparative parameters and deposition conditions. The reactant concentration, pH, deposition temperature, and rate of agitation were found to influence significantly the quality and thickness of the films. The photoconductive studies have been done with the help of rise and decay curves. Lifetime, mobility, and trap depth are calculated for observed parameters. Band gap measurements for the prepared films have been done with the help of optical transmission spectra using UV-VIS-IR spectrophotometer (190–1100 Å). Interesting results of PC rise and decay studies, optical absorption, and transmission spectra have been presented and discussed. Mobility is influenced significantly by Sn composition. The action spectra showed displacement in the absorption edge towards lower energy side by the addition of Sn mole content. The energy gap decreased from 2.1 to 1.9 eV for x = 0.01 and 1.85 eV for x = 0.02.     

Analytical model for the optical functions of indium gallium nitride with application to thin film solar photovoltaic cells

This paper presents the preliminary results of optical characterization using spectroscopic ellipsometry of wurtzite indium gallium nitride (In_xGa_1−xN) thin films with medium indium content (0.38 < x < 0.68) that were deposited on silicon dioxide using plasma-enhanced evaporation. A Kramers-Kronig consistent parametric analytical model using Gaussian oscillators to describe the absorption spectra has been developed to extract the real and imaginary components of the dielectric function (?₁, ?₂) of In_xGa_1−xN films. Scanning electron microscope (SEM) images are presented to examine film microstructure and verify film thicknesses determined from ellipsometry modeling. This fitting procedure, model, and parameters can be employed in the future to extract physical parameters from ellipsometric data from other In_xGa_1−xN films.     

Aluminum scandium nitride thin-film bulk acoustic resonators for wide band applications

Piezoelectric c-textured Al_(1−x)Sc_xN thin films, where the Sc relative concentration, x, varies in the range 0–0.15 have been studied in view of radio frequency (RF) electro-acoustic applications. Thin film bulk acoustic wave resonators (FBARs) employing these films were fabricated and characterized as a function of the Sc concentration for the first time. The measured electromechanical coupling is found to increase by as much as 100% in the above concentration range. The results from this work underline the potential of the c-textured Al_(1−x)Sc_xN based FBARs for wide band RF applications.     

Investigations on the optical properties of sol–gel derived lanthanum doped lead titanate thin films

In the present work we studied the optical properties of undoped and La doped lead titanate thin films, and also demonstrated that the optical characterization of thin films can be used as an effective diagnostic tool to assess film quality. The optical properties of Pb_1−xLa_xTi_1−x/4O₃ [where x=0 (undoped), 10, 15, 20, 25 and 30 at.%] thin films were investigated using both transmission and reflection spectra in the 200–900-nm wavelength range. The refractive index (n), extinction coefficient (k) and the thickness of the film (d_f) were determined from the measured transmission spectra. The thickness of the film obtained from the interference fringes in transmission or reflection spectra matched well with those obtained from other methods. The appearance of interference fringes is an indication of the thickness uniformity of the film. The low value of extinction coefficient (in the order of 10⁻²) as observed in our films is a qualitative indication of excellent surface smoothness of the films. The densities of the films were estimated from their refractive indices using effective medium approximation. The average oscillator strength and its associated wavelength were estimated using a Sellmeier-type dispersion equation. Absorption coefficient (α) and the band-gap energy (E_g) were obtained for undoped and La doped films with varying La concentration. It was found that the refractive index and packing fraction values decrease with La doping. La doping was found to decrease the grain size of the films and increase the density of individual grains. Increased La content led to clustering of smaller grains. The observed variation of band-gap energy with La doping has been correlated to the observed microstructure of these films.     

Effect of tellurium addition on the optical and physical properties of germanium selenide glassy semiconductors

Thin films of the glasses Ge₁₀ Se_90−x Te_x (0 ≤ x ≥ 40) have been prepared by melt quenching technique; thin films were evaporated at a pressure of ≈10⁻⁴ Pa. The optical absorption behavior of these thin films was studied from the reflection and transmission spectrum in the spectral range 200-1200 nm. The optical constants i.e optical band gap (E_opt), absorption coefficient, refractive index (n) are calculated. The optical band gap has been estimated using Tauc extrapolation and found to decrease with Te content. The Dispersion of refractive index has been studied in terms of Wemple - Di Domenico model. The value of static refraction index has been found to increase with Te content. The distribution of the possible chemical bonds has been calculated. The obtained results were correlated with the character of the chemical bond for the prepared compositions through a study of parameters such as average heat of atomization (Hs), the cohesive energies of the bonds (CE), The mean bond energy <E> and average coordination number (m).     

Effects of niobium content on electrical and mechanical properties of (Na0.85K0.15)0.5Bi0.5Ti(1-x)Nb x O3 thin films

(Na_0.85K_0.15)_0.5Bi_0.5Ti_(1-x)Nb _x O₃ (NKBT-N100x) thin films were deposited on Pt/Ti/SiO₂/Si(100) substrates by metal–organic decomposition method and annealed in oxygen atmosphere at 750 °C. The effects of niobium concentration on the microstructures, ferroelectric, piezoelectric, leakage current and mechanical properties of the NKBT-N100x (x = 0, 0.01, 0.03, 0.05) thin films have been investigated in detail. The NKBT-3N thin film has the largest remnant polarization (7 μC/cm²) and statistically averaged d _33eff (140 pm/V), the smallest leakage current, elasticity modulus (102.0 Gpa), hardness (5.1 Gpa) and residual stress (297.0 Mpa). The evaluation of residual stresses of these thin films will offer useful guidelines of safe working condition for their potential application in microelectromechanical system.     

Spectroscopic ellipsometry studies of amorphous PZT thin films with various Zr/Ti stoichiometries

Amorphous stoichiometric Pb(Zr _x Ti_{1 – x)}O₃) (PZT) thin films with various values of x were deposited on Si(100) substrates by the sol-gel technique. The influence of Ti content on the optical properties was studied by spectroscopic ellipsometry (SE) in the UV-visible region. Using a four-phase fitting model, the refractive index n and extinction coefficient k was obtained by analyzing the SE spectra. The optical band gap energies E _g for these films were reported under the assumption of a direct band-to-band transition. It has been found that the refractive index, extinction coefficient and band gap energy of the films were functions of the film compositions. The refractive index of the PZT films increases linearly with increasing Ti content. On the other hand, the optical band gap energy of the PZT films decreases with increasing Ti content.     

Determination of the optical constants of amorphous AsxS100−x films using effective-medium approximation and OJL model

The transmission spectra were used to obtain an efficient parameterization of the spectral dependences of the optical constants of amorphous As–S thin films by applying a suitable dielectric function model. For studying the compositional dependence of the optical constants, different compositions of As_xS_100−x (x = 10, 15, 20, 25, 30 and 40 at%) thin films were deposited by thermal evaporation technique in a base pressure of 7.5 × 10⁻⁶ Torr at room temperature. The transmission spectra (measured in the wavelength range of 0.2–0.9 μm) were analyzed by applying O’Leary, Johnson, and Lim (OJL) model based on the joint density of states (JDOS) functions. However, the best fit of the optical data was obtained by considering the two-layer configuration film; the top layer was assumed to be consisted of a bulk AsS material embedded in voids (air). Therefore, OJL model along with Bruggeman effective-medium approximation (BEMA) model was used to determine the effective optical constants of the As–S thin films. The photon energy dependence of the dielectric function, ? = ?_r − i?_i of the investigated As–S films was presented. The film thickness, absorption coefficient α, refractive index n, extinction coefficient k, static refractive index n(0) and optical band gap E_g have been deduced. It was found that with the increase in arsenic content up to the stoichiometric As₄₀S₆₀, the indirect optical energy gap decreases, while the refractive index increases.     

Band alignment of Cd(1 − x)ZnxS produced by spray pyrolysis method

Cd_(1 − x)Zn_xS thin films have been grown on glass substrates by the spray pyrolysis method using CdCl₂ (0.05 M), ZnCl₂ (0.05 M) and H₂NCSNH₂ (0.05 M) solutions and a substrate temperature of 260 °C. The energy band gap, which depends on the mole fraction × in the spray solution used for preparing the Cd_(1 − x)Zn_xS thin films, was determined. The energy band gaps of CdS and ZnS were determined from absorbance measurements in the visible range as 2.445 eV and 3.75 eV, respectively, using Tauc theory. On the other hand, the values calculated using Elliott-Toyozawa theory were 2.486 eV and 3.87 eV, respectively. The exciton binding energies of Cd_0.8Zn_0.2S and ZnS determined using Elliott-Toyozawa theory were 38 meV and 40 meV, respectively. X-ray diffraction results showed that the Cd_(1 − x)Zn_xS thin films formed were polycrystalline with hexagonal grain structure. Atomic force microscopy studies showed that the surface roughness of the Cd_(1 − x)Zn_xS thin films was about 50 nm. Grain sizes of the Cd_(1 − x)Zn_xS thin films varied between 100 and 760 nm.     

Aluminum scandium nitride thin-film bulk acoustic resonators for wide band applications

Piezoelectric c-textured Al_(1−x)Sc_xN thin films, where the Sc relative concentration, x, varies in the range 0-0.15 have been studied in view of radio frequency (RF) electro-acoustic applications. Thin film bulk acoustic wave resonators (FBARs) employing these films were fabricated and characterized as a function of the Sc concentration for the first time. The measured electromechanical coupling is found to increase by as much as 100% in the above concentration range. The results from this work underline the potential of the c-textured Al_(1−x)Sc_xN based FBARs for wide band RF applications.     

Electrical and optical properties of reactive sputtered TiO x thin films for uncooled IR detector applications

Nanostructured titanium oxide (nano-TiO _x ) thin films for uncooled IR detectors were fabricated by dc reactive magnetron sputtering and post-deposition annealed in oxygen atmosphere. The crystalline structure and surface morphology were characterized by glancing incidence X-ray diffraction (GIXRD) and field emission scanning microscopy. The results of GIXRD measurements indicate that TiO _x thin film deposited at room temperature is amorphous. A mixture of anatase and rutile nanocrystalline structure phase were present in oxygen annealed TiO _x thin film. A weak absorption peak around 438 cm^?1 corresponding to Ti–O stretching vibration is observed by Fourier transform infrared spectroscopy with annealed TiO _x thin film. The X-ray photoelectron spectra reveals Ti³⁺ and Ti⁴⁺ ions are coexisting in TiO _x films. The optical spectra of the films indicate that the optical absorption edge of the nano-TiO _x film exhibits a red shift compared to the as-deposited film. Furthermore, compared to bulk TiO _x , a blue shift was observed in both of the deposited and annealed films due to quantum size effect. The dependence of resistivity on temperature reveals both the absolute value of temperature coefficient of resistivity (TCR) and activation energy of TiO _x thin film increase significantly after annealing in oxygen.