Physical properties of flash evaporated In2O3 films prepared at different substrate temperatures

Indium oxide (In₂O₃) thin films were prepared by flash evaporated technique under various substrate temperatures in the range of 303-673 K and systematically studied the structural, electrical and optical properties of the deposited films. The films formed at substrate temperatures of < 373 K were amorphous while those deposited at higher substrate temperatures (≥ 373 K) were polycrystalline in nature. The optical band gap of the films decreased from 3.71 eV to 2.86 eV with the increase of substrate temperature from 303 K to 673 K. Figure of merit of the films increased from 2.8 × 10³ Ω^− 1 cm^− 1 to 4.2 × 10³ Ω^− 1 cm^− 1 with increasing substrate temperature from 303 K to 573 K, thereafter decreased to 2.2 × 10³ Ω^− 1 cm^− 1 at higher temperature of 673 K.     

Characterization of stepwise flash-evaporated CuInSe2 films

CuInSe₂ (CIS) films were deposited by stepwise flash evaporation from polycrystalline powder source onto glass substrates held at various temperatures ranging from 100 to 560 K. The phase purity and microstructure were analyzed by transmission electron microscopy. The investigations show that films grown at 300 K and below were amorphous, whereas those grown at 370 K and above were polycrystalline in nature. The grain size in polycrystalline films were found to improve with increase in substrate temperature and during post-deposition annealing. The films had near stoichiometric composition as revealed by Rutherford backscattering spectrometry. Analysis of the optical transmittance spectra of CIS films deposited at 520 K yielded a value of ∼0.97 eV for the fundamental band gap.     

The optical properties of Bi3.25La0.75Ti3O12 thin films with different thickness prepared by chemical solution deposition

Bi_3.25La_0.75Ti₃O₁₂(BiLT) thin films with different thickness were successfully deposited onto fused quartz by chemical solution deposition. X-ray diffraction analysis shows that BiLT thin films are polycrystalline with (0 0 2)-preferred orientation. The dispersion of refractive indices of the BiLT thin films was investigated by the optical transmittance spectrum. The optical band gap energy was estimated from the graph of (hνα)² versus hν. The results show that the refractive index and band-gap energy of the BiLT thin films decrease with the films thickness.     

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.     

Copper nitride films deposited by dc reactive magnetron sputtering

Copper nitride (Cu₃N) films were deposited on glass substrates by sputtering of copper target under various substrate temperatures in the range 303–523 K using dc reactive magnetron sputtering. The substrate temperature highly influenced the structural, mechanical, electrical and optical properties of the deposited films. The X-ray diffraction measurements showed that the films were of polycrystalline nature and exhibit preferred orientation of (111) phase of Cu₃N. The microhardness of the films increased from 2.7 to 4.4 GPa with the increase of substrate temperature from 303 to 473 K thereafter decreased to 4.1 GPa at higher temperature of 523 K. The electrical resistivity of the films decreased from 8.7 × 10⁻¹ to 1.1 × 10⁻³ Ωcm and the optical band gap decreased from 1.89 to 1.54 eV with the increase of substrate temperature from 303 to 523 K respectively.     

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 and selenization temperatures on the growth of Cu2SnSe3 films

The effects of substrate temperature and selenization temperature on the structure, composition, electrical and optical properties of Cu₂SnSe₃ films were studied systematically. Cu₂SnSe₃ films deposited at various substrate temperatures (303–573 K) by the flash evaporation method are found to be non-stoichiometric. To compensate the selenium deficiency and obtain a single-phase, an annealing Cu₂SnSe₃ films deposited at 573 K was performed in selenium atmosphere. Cu₂SnSe₃ films deposited at a substrate temperature of 573 K and then selenized at 673 K were single phase and polycrystalline exhibiting monoclinic structure. The films showed p-type conductivity with a direct band gap of 0.84 eV.     

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).     

Substrate bias voltage influenced structural, electrical and optical properties of dc magnetron sputtered Ta2O5 films

Tantalum oxide (Ta₂O₅) films were formed on silicon (111) and quartz substrates by dc reactive magnetron sputtering of tantalum target in the presence of oxygen and argon gases mixture. The influence of substrate bias voltage on the chemical binding configuration, structural, electrical and optical properties was investigated. The unbiased films were amorphous in nature. As the substrate bias voltage increased to −50 V the films were transformed into polycrystalline. Further increase of substrate bias voltage to −200 V the crystallinity of the films increased. Electrical characteristics of Al/Ta₂O₅/Si structured films deposited at different substrate bias voltages in the range from 0 to −200 V were studied. The substrate bias voltage reduced the leakage current density and increased the dielectric constant. The optical transmittance of the films increased with the increase of substrate bias voltage. The unbiased films showed an optical band gap of 4.44 eV and the refractive index of 1.89. When the substrate bias voltage increased to −200 V the optical band gap and refractive index increased to 4.50 eV and 2.14, respectively due to the improvement in the crystallinity and packing density of the films. The crystallization due to the applied voltage was attributed to the interaction of the positive ions in plasma with the growing film.     

Influence of laser-irradiation on the optical constants Se75S25 − xCdx thin films

Amorphous thin films of glassy alloys of Se₇₅S_25 − xCd_x (x = 2, 4 and 6) were prepared by thermal evaporation onto chemically cleaned glass substrates. Optical absorption and reflection measurements were carried out on as-deposited and laser-irradiated thin films in the wavelength region of 500-1000 nm. Analysis of the optical absorption data shows that the rule of no-direct transitions predominates. The laser-irradiated Se₇₅S_25 − xCd_x films showed an increase in the optical band gap and absorption coefficient with increasing the time of laser-irradiation. The results are interpreted in terms of the change in concentration of localized states due to the shift in Fermi level. The value of refractive index increases decreases with increasing photon energy and also by increasing the time of laser-irradiation. With the large absorption coefficient and change in the optical band gap and refractive index by the influence of laser-irradiation, these materials may be suitable for optical disc application.     

Reactive DC magnetron sputter deposited copper nitride nano-crystalline thin films: Growth and characterization

CuN_x thin films were grown by reactive DC magnetron sputtering and their structural, morphological, optical and electrical properties were evaluated. This study provides insight into the importance of substrate temperature and nitrogen content on the characteristic of CuN_x films. Phase analysis and structural properties of these films were identified by X-ray diffraction (XRD) technique. XRD results showed that the CuN_x films were single phase and polycrystalline with mixed orientation. Nitrogen excess accommodates in vacant interstitial sites of cubic anti-ReO₃ crystal structure of CuN_x and exhibits a solid solubility. The variation of surface morphology, studied by scanning electron microscope (SEM), shows suppression of the pyramidal-like grain growth by N richness. Optical study were performed by UV-Vis-near IR transmittance spectroscopy. Film thickness, refractive index and extinction coefficient were extracted from the measured transmittance using a reversed engineering method. Absorption coefficient and electrical resistivity indicate that the CuN_x films present extrinsic semiconducting behavior with an indirect optical band gap between 1.19 and 1.44 eV. To confirm the optical band gap energy, a first principle calculation was performed and compared with the measured data.     

Effect of chopping on the properties of bismuth oxide thin films

Nanocrystalline bismuth oxide thin films have been deposited by thermal oxidation, in air, of vacuum evaporated chopped bismuth thin films. The optical properties and adhesion have been studied. The oxidation temperature and duration were varied. As revealed by structural investigations, polycrystalline and multiphase bismuth oxide thin films were obtained. At all oxidation temperatures, monoclinic Bi₂O₃ is predominant. The films showed high transmittance in the visible range of spectrum. The direct band gap of the films obtained was between 2.78 eV and 3.04 eV. The refractive index observed is in the range 1.934 to 2.096. The adhesion of films was in the range 215 × 10² to 470 × 10² kgF/cm². The values are strongly influenced by the heat treatment characteristics. It was observed that chopping helps in improving the adhesion and increasing refractive index, packing density and band gap of bismuth oxide thin films. These bismuth oxide films can have potential use in optical waveguides.     

Characterization of Tin disulphide thin films prepared at different substrate temperature using spray pyrolysis technique

Thin films of tin disulphide on glass substrates were prepared by spray pyrolysis technique using precursor solutions of SnCl₂·2H₂O and n–n dimethyl thiourea at different substrate temperatures varied in the range 348–423 K. Using the hot probe technique the type of conductivity is found to be n type. X ray diffraction analysis revealed the polycrystalline nature with increasing crystallinity with respect to substrate temperature. The preferential orientation growth of SnS₂ compound having hexagonal structure along (002) plane increased with the substrate temperature. The size of the tin disulphide crystallites with nano dimension were determined using the Full Width Half Maximum values of the Bragg peaks and found to increase with the substrate temperature. The surface morphology had been observed on the surface of these films using scanning electron microscope. The optical absorption and transmittance spectra have been recorded for these films in the wavelength range 400–800 nm. Thickness of these films was found using surface roughness profilometer. The absorption coefficient (α) was determined for all the films. Direct band gap values were found to exist in all the films deposited at different substrate temperatures. The value of room temperature resistivity in dark decreased from 5.95 × 10³ Ω cm for the amorphous film deposited at low temperature (348 K) to 2.22 × 10³ Ω cm for the polycrystalline film deposited at high temperature (423 K) whereas the resistivity values in light decreased from 1.48 × 10³ to 0.55 × 10³ Ω cm respectively, which is determined using the four probe method. Activation energy of these thin films was determined by Arrhenius plot.     

Structural and optical analysis of nanocrystalline thin films of mixed rare earth oxides (Y1-xErx)2O3

Nanocrystalline thin films of mixed rare earth oxides (Y_1-xEr_x)₂O₃(0.1 ≤ x ≤ 1) were deposited by electron beam evaporation technique on polished fused silica glass at different substrate temperatures (200-500 °C). The effect of the substrate temperature as well as the mixing parameter (x) on the structural and optical properties of these films has been investigated by using X-ray diffraction (XRD), energy dispersive x-ray analysis and optical spectrophotometry. XRD investigation shows that mixed rare earth oxides film (Y_1-xEr_x)₂O₃ grown at lower substrate temperature (T_s ≤ 300 °C) are poorly crystalline, whereas films grown at higher substrate temperatures (T_s ≥ 400 °C) tend to have better crystallinity. Furthermore, the mixing parameter (x) was found to stabilize the cubic phase over the entire of 0.1 ≤ x ≤ 1. The crystallite size of the films was found to vary in the range from 25 to 39 nm. Optical band gap of the films was deterimined by analysis of the absoprtion coeffifcient. For films deposited at different substrate temperatures direct and indirect transitions occur with energies varied from 5.29 to 5.94 eV and from 4.23 to 4.51 eV, respectively. However, films of different composition x, give optical band gap varied from 6.14 to 5.86 eV for direct transition and from 5.23 to 4.22 eV for indirect transitions. Consequently, one may conclude that it is possible to tune the energy band gap by relative fraction of constituent oxides. It was found that optical constants increase with increasing the substrate temperature. Nevertheless, the values of n and k decrease with increasing the mixing parameter, x.     

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.     

Mg-composition induced effects on the physical behavior of sprayed Zn1−xMgxO films

Thin films of Zn_1 − xMg_xO, with Mg compositions in the range, 0 < x < 0.4, have been deposited onto soda-lime glass substrates using chemical spray pyrolysis. The effects of altering the alloy composition on the chemical and physical properties of the layers were investigated using X-ray photoelectron spectroscopy, atomic force microscopy, Raman, optical and electrical measurements. The data shows systematic shifts in the properties of the layers with Mg-content. In particular, the optical absorption data showed that the influence of Mg-content on the energy gap of Zn_1 − xMg_xO films is significant. Layers with x = 0.24 had an optical energy band gap, E_g = 3.87 eV. The best layers produced had properties appropriate for application as Cd-free buffer layers in copper indium gallium selenide (CIGS) solar cells.     

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.     

Structural, optical, and magnetic properties of Fe-doped ZnO films prepared by spray pyrolysis method

Zn_1−xFe_xO thin films with different Fe content were deposited on glass substrates at 450 °C by spray pyrolysis technique. The effect of doping on the structural and optical properties of ZnO films was investigated. X-ray diffraction has shown that the films are polycrystalline and textured with the c-axis of the wurtzite structure along the growth direction. Scanning electron microscopy has shown that the surface of the films are homogeneous. The magnetic measurements performed at 5 K using a SQUID magnetometer showed the co-existence of paramagnetic, antiferromagnetic and ferromagnetic contributions.     

Structural and chemical transformations in SnS thin films used in chemically deposited photovoltaic cells

Chemically deposited SnS thin films possess p-type electrical conductivity. We report a photovoltaic structure: SnO₂:F-CdS-SnS-(CuS)-silver print, with V_oc > 300 mV and J_sc up to 5 mA/cm² under 850 W/m² tungsten halogen illumination. Here, SnO₂:F is a commercial spray-CVD (Pilkington TEC-8) coating, and the rest deposited from different chemical baths: CdS (80 nm) at 333 K, SnS (450 nm) and CuS (80 nm) at 293-303 K. The structure may be heated in nitrogen at 573 K, before applying the silver print. The photovoltaic behavior of the structure varies with heating: V_oc ≈ 400 mV and J_sc < 1 mA/cm², when heated at 423 K in air, but V_oc decreases and J_sc increases when heated at higher temperatures. These photovoltaic structures have been found to be stable over a period extending over one year by now. The overall cost of materials, simplicity of the deposition process, and possibility of easily varying the parameters to improve the cell characteristics inspire further work. Here we report two different baths for the deposition of SnS thin films of about 500 nm by chemical deposition. There is a considerable difference in the nature of growth, crystalline structure and chemical stability of these films under air-heating at 623-823 K or while heating SnS-CuS layers, evidenced in XRF and grazing incidence angle XRD studies. Heating of SnS-CuS films results in the formation of SnS-Cu_xSnS_y. ‘All-chemically deposited photovoltaic structures’ involving these materials are presented.     

Optical constants of electroplated Bi2Te3 films by Mueller matrix spectroscopic ellipsometry

We synthesized polycrystalline Bi_2 + xTe_3 − x (− 0.2< x <0.2) thin films by electrodeposition in acidic medium. Since Bi₂Te₃-like structure may be uniaxially anisotropic due to its rhombohedral crystallographic system, we investigated their optical behavior using ex and in situ Mueller matrix spectroscopic ellipsometry in the wavelength range of 470 to 830 nm (1.5-2.6 eV). We found that room-temperature electroplated polycrystalline appears optically isotropic and that no depolarization effect occurs from the first steps of growth until several micrometers thick films. Additional ex situ measurements permit to obtain their optical constants from far-ultraviolet to near-infrared (190-2100 nm).