Study of flash evaporated CuIn1 − xGaxTe2 (x = 0, 0.5 and 1) thin films

CuIn_1 − xGa_xTe₂ thin films with x = 0, 0.5 and 1, have been prepared by flash evaporation technique. These semiconducting layers present a chalcopyrite structure. The optical measurements have been carried out in the wavelength range 200-3000 nm. The linear dependence of the lattice parameters as a function of Ga content obeying Vegard's law was observed. The films have high absorption coefficients (4 · 10⁴ cm^− 1) and optical band gaps ranging from 1.06 eV for CuInTe₂ to 1.21 eV for CuGaTe₂. The fundamental transition energies of the CuIn_1 − xGa_xTe₂ thin films can be fitted by a parabolic equation namely E_g1(x) = 1.06 + 0.237x − 0.082x². The second transition energies of the CuInTe₂ and CuGaTe₂ films were estimated to be: E_g2 = 1.21 eV and E_g2 = 1.39 eV respectively. This variation of the energy gap with x has allowed the achievement of absorber layers with large gaps.     

Chemical states of carbon in amorphous boron carbide thin films deposited by radio frequency magnetron sputtering

Boron carbide thin films were deposited by radio frequency (RF) magnetron sputtering and characterized by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and high resolution transmission electron microscopy. The results reveal that the structure of thin films deposited at substrate temperatures lower than 350 °C is amorphous. We found that there are four chemical states for carbon in amorphous boron carbide thin films deposited by RF magnetron sputtering. One is the segregated carbon in form of the graphitic inclusions in the thin film identified by Raman spectroscopy and Raman mapping using two strong peaks at ~ 1360 cm^− 1 and ~ 1590 cm^− 1, but the XPS results show that the graphitic inclusions do not connect to the substrate directly. On the surface the carbon forms C=O bonds characterized by the peak of C1s core level at 285.0 eV besides B-C bonds in the boron carbide with the peak of C1s being at 282.8 eV. The detailed analysis of B-C bonds in the boron carbide shows that there are two states for carbon atoms in B-C bonds: in the C-B-C models with C1s peak at 282.3 eV and in the icosahedra with C1s peak at 283.3 eV.     

Study of structural and optical properties of Cd1-xZnxSe thin films

Cd_1-xZn_xSe (x = 0, 0.5 and 1) thin films have been deposited onto glass substrates using thermal evaporation technique. The lattice constants, grain size, microstrain and dislocation density were studied by using X-ray diffraction. In addition the optical constants were calculated in the wavelength range 400-2500 nm. Transmittance and reflectance were used to calculate the absorption coefficient α and the optical band gap E_g. The linear relation of (αhυ)² as a function of photon energy hυ for the thin films illustrated that the films exhibit a direct band gap, which increases with increasing Zn content. This increasing of optical band gap was interpreted in accordance to the increasing in the cohesive energy. Optical constants, such as refractive index n, optical conductivity σ_opt, complex dielectric constant, relaxation time τ and dissipation factor tanδ were determined. The optical dispersion parameters E₀, E_d were determined according to Wemple and Di Domenico method.     

Growth and characterization of (Pb,La)(Zr,Ti)O3 thin film epilayers on SrTiO3-buffered Si(001)

Ferroelectric Pb_0.92La_0.08Zr_0.4Ti_0.6O₃ (PLZT) thin films were deposited on SrTiO₃-buffered Si(001) substrate by on-axis radio frequency magnetron sputtering. X-ray diffraction analysis revealed epitaxial growth of monocrystalline PLZT films, with an (001) rocking curve full width at half maximum of ∼ 0.3°. φ-scans showed 45° in-plane orientation of the perovskite unit cell relative to that of silicon. The elemental composition of the thin film heterostructure was examined by Auger sputter depth profiling measurements. The recorded profiles suggest that the SrTiO₃ buffer layer serves not only as a template for epitaxial growth, but also as a barrier suppressing Pb-Si interdiffusion between the PLZT layer and the Si substrate. The surface roughness of the PLZT layer was measured at ∼ 4 nm for films with ∼ 500 nm thickness. Wavelength dispersions for the refractive index (n) and the extinction coefficient (k) were obtained from spectroscopic ellipsometry measurements, with n ∼ 2.48 at the main communication wavelength λ = 1550 nm and k < 0.001 for λ > 650 nm. Recorded polarization vs. electric field loops for the PLZT epilayer, with a SrRuO₃ electrode layer interposed between PLZT and SrTiO₃, showed a remnant polarization P_r ≈ 40 µC/cm² and coercive field E_c ≈ 100 kV/cm. These findings suggest that the sputter-deposited PLZT thin films retain the functional properties critical to ferroelectric and electro-optic device applications, also when integrated on a semiconductor substrate.     

Thin film preparation and characterization of wide band gap Cu3TaQ4 (Q = S or Se) p-type semiconductors

The structural, optical, and electronic properties of thin films of a family of wide band gap (E_g > 2.3 eV) p-type semiconductors Cu₃TaQ₄ (Q = S or Se) are presented. Thin films prepared by pulsed laser deposition of ceramic Cu₃TaQ₄ targets and ex-situ annealing of the as-deposited films in chalcogenide vapor exhibit mixed polycrystalline/[100]-directed growth on amorphous SiO₂ substrates and strong (100) preferential orientation on single-crystal yttria-stabilized zirconia substrates. Cu₃TaS₄ (E_g = 2.70 eV) thin films are transparent over the entire visible spectrum while Cu₃TaSe₄ (E_g = 2.35 eV) thin films show some absorption in the blue. Thin film solid solutions of Cu₃TaSe_4 − xS_x and Cu₃TaSe_4 − xTe_x can be prepared by annealing Cu₃TaSe₄ films in a mixed chalcogenide vapor. Powders and thin films of Cu₃TaS₄ exhibit visible photoluminescence when illuminated by UV light.     

Spray pyrolysis deposition of indium sulphide thin films

In₂S₃ thin films were grown by the chemical spray pyrolysis (CSP) method using the pneumatic spray set-up and compressed air as a carrier gas. Aqueous solutions containing InCl₃ and SC(NH₂)₂ at a molar ratio of In/S = 1/3 and 1/6 were deposited onto preheated glass sheets at substrate temperatures T_s = 205-410 °C. The obtained films were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM,) optical transmission spectra, X-ray photoelectron spectroscopy (XPS) and energy dispersive spectroscopy (EDS). According to XRD, thin films deposited at T_s = 205-365 °C were composed of the (0 0 12) orientated tetragonal β-In₂S₃ phase independent of the In/S ratio in the spray solution. Depositions performed at T_s = 410 °C led to the formation of the In₂O₃ phase, preferably when the 1/3 solution was sprayed. Post-deposition annealing in air indicated that oxidation of the sulphide phase has a minor role in the formation of In₂O₃ at temperatures up to 450 °C. In₂S₃ films grown at T_s below 365 °C exhibited transparency over 70% in the visible spectral region and E_g of 2.90-2.96 eV for direct and 2.15-2.30 eV for indirect transitions, respectively. Film thickness and chlorine content decreased with increasing deposition temperatures. The XPS study revealed that the In/S ratio in the spray solution had a significant influence on the content of oxygen (Me-O, BE = 530.0 eV) in the In₂S₃ films deposited in the temperature range of 205-365 °C. Both XPS and EDS studies confirmed that oxygen content in the films deposited using the solution with the In/S ratio of 1/6 was substantially lower than in the films deposited with the In/S ratio of 1/3.     

Study of GeYSi1 − Y:H films deposited by low frequency plasma

In this work, we report a study of the optical properties measured through spectral transmission and spectroscopic ellipsometry in Ge:H and Ge_YSi_1 − Y:H (Y ≈ 0.97) films deposited by low frequency (LF) PE CVD with hydrogen (H) dilution. The dilution was varied in the range of R = 20 to 80. It was observed that H-dilution influences in a different way on the interface and bulk optical properties, which also depend on incorporation of silicon. The films with low band tail characterized by its Urbach energy, E_U, and defect absorption, α_D, have been obtained in Ge:H films for R = 50 with E_U = 0.040 eV and α_D = 2 × 10³ cm^− 1 (hν ≈ 1.04 eV), and in Ge_YSi_1 − Y:H films for R=75 with E_U = 0.030 eV and α_D = 5 × 10² cm^− 1 (hν ≈ 1.04 eV).     

Synthesis of AgInSnS4 thin films by adding tin (Sn) into the chalcopyrite structure of AgInS2 using spray pyrolysis

AgInSnS₄ thin films were prepared by adding a tin salt to the starting solution used for preparing chalcopyrite AgInS₂ thin films by spray pyrolysis The AgInSnS₄ films were grown at substrate temperatures in the 300-400 °C range, using an alcoholic solution comprised of silver acetate, indium chloride, tin chloride and thiourea. The tin chloride content in the starting solution was gradually varied in terms of the molar ratio x = [Sn]/([S] + [Ag]) from 0 to 0.5 to obtain Sn-doped chalcopyrite AgInS₂ (x < 0.2) and spinel-like AgInSnS₄ (x = 0.2-0.4). X-ray diffraction studies indicated that AgInSnS₄ has a cubic spinel-like structure with lattice parameter of 10.77 A. All AgInSnS₄ thin films exhibited p-type conduction, and their room temperature conductivity ranged from 10^− 1 to 10^− 2 S/cm. The conductivity versus 1/T plots for this material showed an Arrhenius-like behavior, from which two activation energies of E_a1 = 0.23-0.40 eV and E_a2 = 0.07-0.20 eV were determined. These results suggest that the grain boundary scattering and the ionization of shallow acceptors dominate the charge carrier transport in the sprayed AgInSnS₄ thin films. The AgInSnS₄ absorption spectrum revealed an energy gap around E_g = 1.89 eV, which was associated to direct-allowed transitions. To our knowledge, the quaternary compound has been prepared for the first time using spray pyrolysis.     

Enhanced ferroelectric properties of Pb(Zr0.80Ti0.20)O3/PbO thin films prepared by radio frequency magnetron sputtering

The Pb(Zr_0.80Ti_0.20)O₃ (PZT) thin films with and without a PbO buffer layer were deposited on the Pt(1 1 1)/Ti/SiO₂/Si(1 0 0) substrates by radio frequency (rf) magnetron sputtering method. The PbO buffer layer improves the microstructure and electrical properties of the PZT thin films. High phase purity and good microstructure of the PZT thin films with a PbO buffer layer were obtained. The effect of the PbO buffer layer on the ferroelectric properties of the PZT thin films was also investigated. The PZT thin films with a PbO buffer layer possess better ferroelectric properties with higher remnant polarization (P_r = 25.6 μC/cm²), and lower coercive field (E_c = 60.5 kV/cm) than that of the films without a PbO buffer layer (P_r = 9.4 μC/cm², E_c = 101.3 kV/cm). Enhanced ferroelectric properties of the PZT thin films with a PbO buffer layer is attributed to high phase purity and good microstructure.     

Study of the growth of CuAlS2 thin films on oriented silicon (111)

Within the chalcopyrite family the sulphur based compounds CuMS₂ (M = In, Ga, Al) have attracted much interest in recent years because they show a direct wide band-gap covering from E_gap = 1.53 eV (CuInS₂) over E_gap = 2.43 eV (CuGaS₂) to E_gap = 3.49 eV (CuAlS₂). Therefore they are particularly suitable for optoelectronic as well as photovoltaic applications. The CuAlS₂ semiconductor is one of these compounds and has good luminescent properties and a wide direct gap of 3.5 eV making it suitable for the use as material for light-emitting devices in the blue region of the spectrum. To dig up fully its potential a better understanding of the fundamental properties of the CuAlS₂ film itself is essential, which could be achieved from high-quality single-crystalline materials. So, the aim of this work has been to study the growth of multilayer CuAlS₂ thin films on Si(111) substrates at a substrate temperature of 723 K. One, two and three layers with 60, 120 and 180 nm thicknesses, respectively, were deposited on Si(111) substrate. The effect of the CuAlS₂ layer numbers on the structure, morphology and optical properties of the samples was investigated. The X-ray diffraction studies revealed that all the samples are polycrystalline in nature, single CuAlS₂ phase and exhibiting chalcopyrite structure with a preferred orientation along the (112) direction. However, the sample with three CuAlS₂ layers exhibit the highly oriented (112) plane with grain sizes of 80 nm. So we show that this experimental process affects significantly the structural properties of the CuAlS₂ films. Raman spectroscopic measurements indicated five prominent peaks at 193, 205, 325, 335 and 370 cm^− 1. The possible origin of the 370 cm^− 1 peak was investigated and was found to be some local vibration in the structure. The peaks at 193-205 and 335 cm^− 1 were ascribed to A₁ and B₂ modes, respectively.     

A comparative study of the properties of thermally evaporated CuIn2n + 1S3n + 2 (n = 0, 1, 2 and 3) thin films

CuInS₂, CuIn₃S₅, CuIn₅S₈ and CuIn₇S₁₁ compounds were synthesized by the horizontal Bridgman method using high-purity copper, indium and sulphur elements. Crushed powders of these ingots were used as raw materials for the vacuum thermal evaporation. So, CuIn_2n + 1S_3n + 2 (n = 0, 1, 2, and 3) thin films were deposited by single source vacuum thermal evaporation onto glass substrates heated at 150 °C. The structural, compositional, morphological, electrical and optical properties of the deposited films were studied using X-ray diffraction (XRD), energy dispersive X-ray, atomic force microscopy and optical measurement techniques. XRD results revealed that all the films are polycrystalline. However, CuInS₂ and CuIn₃S₅ films had a chalcopyrite structure with preferred orientation along 112 while CuIn₅S₈ and CuIn₇S₁₁ films exhibit a spinel structure with preferred orientation along 311. The absorption coefficients of the all CuIn_2n + 1S_3n + 2 films are in the range of 10⁻⁴ and 10⁻⁵ cm⁻¹. The direct optical band gaps of CuIn_2n + 1S_3n + 2 layers are found to be 1.56, 1.78, 1.75 and 1.30 eV for n = 0, 1, 2, and 3, respectively. CuIn₃S₅ and CuIn₅S₈ films are p type with electrical resistivities of 4 and 12 Ω cm whereas CuInS₂ and CuIn₇S₁₁ are highly compensated with resistivities of 1470 and 1176 Ω cm, respectively.     

Optical properties and DC electrical conductivity of Ge28−xSe72Sbx thin films

Thin films of Ge_28−xSe₇₂Sb_x (x=0, 8, 16, 24 at%) with thickness of 200 nm are prepared by thermal evaporation onto glass substrates under vacuum of 5.3×10⁻⁵ mbar. Optical reflectance and transmittance of these films are measured at room temperature in the light wavelength region from 200 to 1100 nm. The estimated optical energy gap, E_g, is found to decrease from 2 eV (0 at% Sb) to 1.5 eV (24 at% Sb), whereas the band tail width, E_e, increases from 0.062 to 0.077 eV, respectively. The refractive index, n, and extinction coefficient, κ, are determined as functions of wavelength. The DC electrical conductivity, σ, of films is measured as a function of temperature in the range from 300 to 360 K. The extracted value of activation energy, ΔE, is found to decrease from 0.95 eV (0 at% Sb) to 0.74 eV (24 at% Sb). Optical and electrical behavior of films can be explained in terms of cohesive energy (CE) and Se-Se defect bonds.     

Growth and characterization of Ba(Cd1/3Ta2/3)O3 thin films

We have synthesized stoichiometric Ba(Cd_1/3Ta_2/3)O₃ [BCT] (100) dielectric thin films on MgO (100) substrates using Pulsed Laser Deposition. Over 99% of the BCT film was found to be epitaxial [BCT (100) || MgO (100) and BCT (010) || MgO (010)] when grown with an elevated substrate temperature of 635 °C, an enhanced oxygen pressure of 53 Pa and a Cd-enriched BCT target with a 1 mol BCT: 1.5 mol CdO composition. A dielectric constant of 32 was inferred from low-frequency capacitance measurements of a planar interdigital metal pattern. Analysis of ultra violet optical absorption results indicates that BCT has a bandgap of 4.9 eV; while the interference pattern in the visible range is consistent with a refractive index of 2.1. Temperature-dependent electrical measurements indicate that the BCT films have a room temperature conductivity of 3 × 10^− 12 Ω^− 1 cm^− 1 with a thermal activation energy of 0.7 eV. A mean particle size of ~ 100 nm and a root mean square surface roughness of 5 to 6 nm were measured using Atomic Force Microscopy.     

Structural, optical, and electrical properties of tin sulfide thin films grown by spray pyrolysis

Tin sulfide (SnS) thin films have been prepared by spray pyrolysis (SP) technique using tin chloride and N, N-dimethylthiourea as precursor compounds. Thin films prepared at different temperatures have been characterized using several techniques. X-ray diffraction studies have shown that substrate temperature (T_s) affects the crystalline structure of the deposited material as well as the optoelectronic properties. The calculated optical band gap (E_g) value for films deposited at T_s = 320-396 °C was 1.70 eV (SnS). Additional phases of SnS₂ at 455 °C and SnO₂ at 488 °C were formed. The measured electrical resistivity value for SnS films was ∼ 1 × 10⁴ Ω-cm.     

Blue shift of optical band-gap in LiNbO3 thin films deposited by sol-gel technique

Lithium niobate (LN) thin films were deposited on quartz substrates by sol-gel technique. The measured absorption and photoluminescence spectra show that the band structure of LN thin films is direct unlike indirect band-gap in bulk LN and the optical band-gap of these LN thin films was measured to be 4.7 eV which is ~ 1 eV greater than that for stoichiometric bulk LN. The dependence of the blue shift of band-gap on several parameters like quantum confinement, composition (Li:Nb ratios of LN thin films) and strain was also investigated. The results obtained show that the large blue shift in band-gap of LN thin films is primarily due to strain in the film.     

Room temperature deposition of ZnSe thin films by successive ionic layer adsorption and reaction (SILAR) method

The zinc selenide (ZnSe) thin films are deposited onto glass substrate using relatively simple and inexpensive successive ionic layer adsorption and reaction (SILAR) method. The films are deposited using zinc acetate sodium selenosulphate precursors. The concentration, pH, immersion and rinsing times and number of immersion cycles have been optimized to obtain good quality ZnSe thin films. The X-ray diffraction (XRD) study and scanning electron microscopy (SEM) studies reveals nanocrystalline nature alongwith some amorphous phase present in ZnSe thin films. Energy dispersive X-ray (EDAX) analysis shows that the films are Se deficient. From optical absorption data, the optical band gap ‘E_g’ for as-deposited thin film was found to be 2.8 eV and electrical resistivity in the order of 10⁷ Ω cm.     

Iodization of antimony thin films: XRD, SEM and optical studies of nanostructured SbI3

Antimony films of thicknesses of 25, 40 and 80 nm deposited using thermal evaporation technique were annealed at 200 °C for 6 h. Programmed iodization was carried out at room temperature for periods ranging from 5 min to 9 h on both as-deposited and annealed films. X-ray diffraction studies on iodized films reveal that antimony tri-iodide nanoparticles grow only on annealed antimony films. Surface morphology as revealed through SEM consists of antimony and antimony tri-iodide nanoparticles are 25 nm and 1 μm, respectively. Optical absorption of Sb and SbI₃ nanoparticles carried out at room temperature. As-deposited antimony film of thickness 25 nm exhibits a sharp rise in the absorption near ultraviolet region while post-deposition annealed films were characterized by red shifted absorption. Interestingly 45 nm thick Sb films exhibit a broad volume plasmon resonance peak around 500 nm with a width of 200 nm. Progressive iodization of 25 nm thick film reveals two absorption bands at 381.7 nm (A₂) and 458.3 nm (B₃) with photon energies 3.25 and 2.70 eV, respectively, due to the development of SbI₃ valence band structure. Last members of hydrogen-like series of absorption levels A₂ and B₃ due to halogen doublet (3/2, 1/2) splitting have been observed at room temperature.     

Dielectric oxynitride LaTiOxNy thin films deposited by reactive radio-frequency sputtering

LaTiO_xN_y thin films have been deposited by RF sputtering on (001) Nb-doped SrTiO₃ and (001) MgO single-crystalline substrates at high temperature (T_S = 800 °C) under different nitrogen ratios in the plasma (vol.% N₂ = 0, 25, 71). The band gaps ranged from E_g = 3.30 eV for the epitaxial transparent film containing no nitrogen to E_g = 2.65 eV for the textured coloured film containing a moderate amount of nitrogen. Dielectric characterization in the frequency range [100 Hz-1 MHz], using a metal-insulator-metal structure, has shown a stable permittivity and loss tangent of the epitaxial low-nitrided LaTiO_xN_y film with values of ε′ = 135 and tanδ = 1.2 10^− 2 at 100 kHz (RT).     

Physical properties of very thin SnS films deposited by thermal evaporation

SnS films with thicknesses of 20-65 nm have been deposited on glass substrates by thermal evaporation. The physical properties of the films were investigated using X-ray diffraction (XRD), scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and ultraviolet-visible-near infrared spectroscopy at room temperature. The results from XRD, XPS and Raman spectroscopy analyses indicate that the deposited films mainly exhibit SnS phase, but they may contain a tiny amount of Sn₂S₃. The deposited SnS films are pinhole free, smooth and strongly adherent to the surfaces of the substrates. The color of the SnS films changes from pale yellow to brown with the increase of the film thickness from 20 nm to 65 nm. The very smooth surfaces of the thin films result in their high reflectance. The direct bandgap of the films is between 2.15 eV and 2.28 eV which is much larger than 1.3 eV of bulk SnS, this is deserving to be investigated further.     

Optical constants of silicone-like (Si:Ox:Cy:Hz) thin films deposited on quartz using hexamethyldisiloxane in a remote RF hollow cathode discharge plasma

Deposition of amorphous silicone-like (Si:O_x:C_y:H_z) thin films in a remote RF hollow cathode discharge plasma using hexamethyldisoloxane as monomer and Ar as feed gas has been investigated for films optical constants and plasma diagnostic as a function of RF power (100-300 W) and precursor flow rate (1-10 sccm). Plasma diagnostic has been performed using Optical Emission Spectroscopy (OES). The optical constants (refractive index, extinction coefficient and dielectric constant) have been obtained by reflection/transmission measurements in the range 300-700 nm. It is found that the refractive index increases from 1.92 to 1.97 with increasing power from 100 to 300 W, and from 1.70 to 1.92 with increasing precursor flow rate from 1 to 10 sccm. The optical energy band gap E_g and the optical-absorption tail ΔE have been estimated from optical absorption spectra, it is found that E_g decreases from 3.28 to 3.14 eV with power increase from 100 to 300 W, and from 3.54 to 3.28 eV with precursor flow rate increase from 1 to 10 sccm. ΔE is found to increase with applied RF power and precursor flow rate increase. The dependence of optical constants on deposition parameters has been correlated to plasma OES.