Ag2СdSnS4 single crystals as promising materials for optoelectronic

Single crystals of the quaternary single crystals Ag₂CdSnS₄ were grown for the first time using the horizontal gradient freeze technique. Optical spectral and photoelectric properties of obtained crystals were investigated. The band gap energy at 77 K according to the photoconductivity spectra is 1.94 eV. The energy levels of the major donor centers in the band gap were determined. The role of intrinsic defects in the observed dependences is analyzed. The energy levels of the major donor centers in the band gap were determined. A small photoconductivity maximum at low temperature is observed at wavelength λ_m = 640 nm (hν ∼ 1.94 eV); situated in the fundamental absorption band, which unambiguously corresponds to the intrinsic origin of photoconductivity. The increase of the extrinsic photoconductivity with the maximum at λ_m ∼ 800 nm with temperature leads to its domination above 240 K. The observed peculiarity can be explained by the photoexcitation of electrons from the valence band to the donor centers which are empty at high temperatures and with further thermal excitation to the conduction band.     

Optical, electrical and structural properties of Cu2Te thin films deposited by magnetron sputtering

Thin films of Cu₂Te were deposited, at room temperature, on glass substrates by magnetron sputtering from independent Cu and Te sources. This work presents the effect of annealing temperature on the optical, structural, and electrical properties of sputtered Cu₂Te films. Annealing above 300 °C resulted in stoichiometric and near stoichiometric Cu₂Te phases, whereas temperatures above 400 °C yielded films with single Cu₂Te phase. In contrast, annealing at temperatures of 250 °C and below resulted in mixed phases of CuTe, Cu₇Te₅, Cu_1.8Te, and Cu₂Te. Analyses of transmittance and reflectance measurements for Cu₂Te indicate that photon absorption occurs via indirect band transitions for incident photons with energy above the band gap energy and free carrier absorption below the band gap energy. The determined indirect band gap was 0.90 eV and its associated phonon energy was 0.065 eV. Optical phonon scattering was identified as the mechanism through which the momentum is conserved during absorption by free carriers. Electrical measurements show p-type conductivity and highly degenerate semiconducting behavior with a hole carrier concentration p = 5.18 × 10²¹ cm^− 3.     

Dispersive optical constants of thermally deposited AgIn5S8 thin films

AgIn₅S₈ thin films were obtained by the thermal evaporation of AgIn₅S₈ crystals onto ultrasonically cleaned glass substrates. The films are found to exhibit polycrystalline cubic structure. The calculated lattice parameter of the unit cell (a) is 10.78 Å. The transmittance data of the as grown films which was recorded at 300 K in the incidence wavelength (λ) range of 320-1000 nm are used to calculate the refractive, n(λ). The transmittance and reflectance data are also used to calculate the absorption coefficient of the as grown AgIn₅S₈ thin films. The fundamental absorption edge is found to be corresponding to a direct allowed transitions energy band gap. This band-to-band transition energy is found to be 1.78 eV and it is consistent with that reported for AgIn₅S₈ single crystals.     

Growth of crystalline HgCr2S4 thin films at mild reaction conditions

Thin films of crystalline HgCr₂S₄ have been deposited on glass substrates at low temperature as low as 65 °C using a chemical bath deposition method. Typical thickness of the deposited HgCr₂S₄ thin films was 264 nm.The films were composed of closely packed irregular grains of 165-175 nm in diameter. The X-ray diffraction analysis and the selected area electron diffraction analysis revealed the deposited thin films were polycrystalline with highly (2 2 0) preferential orientation. The films exhibit a pure faint black. Their direct band gap energy was 2.39 eV with room temperature electrical resistivity of the order of 10⁻³ Ω cm.     

Electrochemical preparation and characterization of three-dimensional nanostructured Sn2S3 semiconductor films with nanorod network

Three-dimensional (3D) nanostructured Sn₂S₃ semiconductor films have been prepared on ITO-coated glass substrates by potentiostatic electrodeposition at −0.80 V (vs. SCE) from a novel plating bath containing K₄P₂O₃ as a complexing agent and Na₂SO₃ as a stabilizing agent and by subsequent annealing. Results showed that the annealing drove the as-deposited Sn₂S₃ films to grow from a granular structure into a nanorod network structure. The nanorods were around 50-100 nm in diameter and 1000 nm in length. The band gap of the annealed film was 1.65 eV and the conductivity was n type. The carrier mobility achieved up to 20.5 cm² V⁻¹ s⁻¹ due to the direct electrical pathways provided by the nanorod network.     

Synthesis of V-doped TiO2 films by chemical bath deposition and the effect of post-annealing on their properties

Amorphous composite films, composed of a Ti_1 − xV_xO₂ solid-solution phase and a V₂O₅ phase, were produced by chemical bath deposition and subsequently air-annealed at various temperatures up to 550 °C. The microstructure and chemical composition of the as-prepared and annealed films were investigated by a combinatorial experimental approach using Scanning electron microscopy, X-ray powder diffraction and X-ray photoelectron spectroscopy. Ultraviolet-Visible Spectrometry was applied to determine the optical band gap of the as-prepared and annealed films. It followed that the incorporation of vanadium in the as-deposited films reduces the optical band gap of TiO₂ from about 3.8 eV to 3.2 eV. Annealing of the films up to 350 °C leads to slight increase of band gap, as attributed to a reduction of the defect density in the initially amorphous oxide films due to the gradual development of long-range order and a concurrent reduction of the V⁴⁺-dopant concentration in the Ti_1 − xV_xO₂ solid-solution phase. The films crystallized upon annealing in air at 550 °C, which resulted in drastic changes of the phase constitution, optical absorbance and surface morphology. Due to the lower solubility of V⁴⁺ in crystalline TiO₂, V⁴⁺ segregates out of the crystallizing Ti_1 − xV_xO₂ solid-solution phase, forming crystalline V₂O₅ at the film surface.     

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.     

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.     

The influence of annealing temperature on the structural, electrical and optical properties of ion beam sputtered CuInSe2 thin films

CuInSe₂ (CIS) thin films were prepared by ion beam sputtering deposition of copper layer, indium layer and selenium layer on BK7 glass substrates followed by annealing at different temperatures for 1 h in the same vacuum chamber. The influence of annealing temperature (100-400 °C) on the structural, optical and electrical properties of CIS thin films was investigated. X-ray diffraction (XRD) analysis revealed that CIS thin films exhibit chalcopyrite phase and preferential (112) orientation when the annealing temperature is over 300 °C. Both XRD and Raman show that the crystalline quality of CIS thin film and the grain size increase with increasing annealing temperature. The reduction of the stoichiometry deviation during the deposition of CIS thin films is achieved and the elemental composition of Cu, In and Se in the sample annealed at 400 °C is very near to the stoichiometric ratio of 1:1:2. This sample also has an optical energy band gap of about 1.05 eV, a high absorption coefficient of 10⁵ cm⁻¹ and a resistivity of about 0.01 Ω cm.     

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.     

Structural and optical properties of amorphous and crystalline antimony sulfide thin-films

Smooth and compact thin films of amorphous and crystalline antimony sulfide (Sb₂S₃) were prepared by radio frequency sputtering of an Sb₂S₃ target. As-deposited films are amorphous. Polycrystalline antimony sulfide films composed of ∼ 500 nm grains are obtained by annealing the as-deposited films at 400 °C in sulfur vapors. Both amorphous and crystalline antimony sulfide have strong absorption coefficients of 1.8 × 10⁵ cm^− 1 at 450 nm and 7.5 × 10⁴ cm^− 1 at 550 nm, and have direct bandgaps with band energies of 2.24 eV and 1.73 eV, respectively. These results suggest the potential use of both amorphous and crystalline antimony sulfide films in various solid state devices.     

Optical properties of sputter deposited transparent and conducting TiO2:Nb films

Transparent and conducting thin films of TiO₂:Nb were prepared on glass by reactive dc magnetron sputtering in Ar + O₂. Post-deposition annealing in vacuum at 450 °C led to good electrical conductivity and optical transparency. The optical properties in the sub-bandgap region were in good agreement with Drude free electron theory, which accounts for intraband absorption. The band gap of the films was found to be in the range of 3.3 to 3.5 eV and signifies the onset of interband absorption. Electrical conductivities in the 10^− 3 Ω cm range were obtained both from dc electrical measurements and from analysis of the optical measurements.     

Optical properties of nanocrystalline SnS2 thin films

Thin films of nanocrystalline SnS₂ on glass substrates were prepared from solution by dip coating and then sulfurized in H₂S (H₂S:Ar = 1:10) atmosphere. The films had an average thickness of 60 nm and were characterized by X-ray diffraction studies, scanning electron microscopy, EDAX, transmission electron microscopy, UV-vis spectroscopy, and Raman spectroscopy. The influence of annealing temperature (150-300 °C) on the crystallinity and particle size was studied. The effect of CTAB as a capping agent has been tested. X-ray diffraction analysis revealed the polycrystalline nature of the films with a preferential orientation along the c-axis. Optical transmission spectra indicated a marked blue shift of the absorption edge due to quantum confinement and optical band gap was found to vary from 3.5 to 3.0 eV with annealing temperature. Raman studies indicated a prominent broad peak at ∼314 cm⁻¹, which confirmed the presence of nanocrystalline SnS₂ phase.     

Photoelectrochemical performance of aluminum-doped AgIn5S8 electrodes created using chemical bath deposition

A solution growth method for the deposition of Al-doped silver-indium-sulfide film electrodes is presented. Structural, optical, and photoelectrochemical (PEC) properties of samples were studied as a function of Al content. An X-ray diffraction pattern of the cubic spinel AgIn₅S₈ phase was obtained for the undoped sample. No Al alloys or other binary compounds that included the Al element were present in Al-doped samples. Images from a scanning electron microscope and atomic ratios of elements in samples from the energy dispersion analysis of X-ray revealed a change of surface morphology and composition for Al-doped samples. The direct band gaps and thicknesses of samples prepared in this study varied from 1.78 to 1.90 eV and from 391 to 293 nm, respectively. The carrier concentration and mobility of samples determined from Hall measurements are in the ranges of 1.02 × 10¹³-1.97 × 10¹⁴ cm^− 3 and 16-75 cm²/Vs, respectively. The maximum photo-enhancement current density of samples reached 3.22 mA/cm² at an external potential of + 1.0 V vs. an Ag/AgCl reference electrode in an aqueous solution containing S²⁻ and SO₃²⁻ ions under illumination using a 300 W Xe lamp system. The experimental results show that Al doping improves the performance of AgIn₅S₈ photo-absorber for the PEC applications with an Al/(Al + In) molar ratio of 0.03 in samples.     

Study on sulfur diffusion in CuInSe2 thin films using two thermal profiles

An insurmountable disadvantage of CuInSe₂ is the low band gap, which limits the open-circuit voltage to value well below 500 mV in solar cells. The incorporation of sulfur into CuInSe₂ thin film was investigated to establish a scientific basis for the graded band gap CuIn(Se_1 − x,S_x)₂ thin films. CuIn(Se_1 − x,S_x)₂ thin films were obtained by reactive annealing of Cu₁₁In₉ precursors in a mixture of sulfur and selenium atmosphere while post-sulfurization of single phase CuInSe₂ did not result in CuIn(Se_1 − x,S_x)₂ thin films. A band gap of 1.36 eV, was obtained for the prepared CuIn(Se_1 − x,S_x)₂.     

Study of optical and structural properties of Cu2ZnSnS4 thin films

Cu₂ZnSnS₄ is a promising semiconductor to be used as absorber in thin film solar cells. In this work, we investigated optical and structural properties of Cu₂ZnSnS₄ thin films grown by sulphurization of metallic precursors deposited on soda lime glass substrates. The crystalline phases were studied by X-ray diffraction measurements showing the presence of only the Cu₂ZnSnS₄ phase. The studied films were copper poor and zinc rich as shown by inductively coupled plasma mass spectroscopy. Scanning electron microscopy revealed a good crystallinity and compactness. An absorption coefficient varying between 3 and 4 × 10⁴cm^− 1 was measured in the energy range between 1.75 and 3.5 eV. The band gap energy was estimated in 1.51 eV. Photoluminescence spectroscopy showed an asymmetric broad band emission. The dependence of this emission on the excitation power and temperature was investigated and compared to the predictions of the donor-acceptor-type transitions and radiative recombinations in the model of potential fluctuations. Experimental evidence was found to ascribe the observed emission to radiative transitions involving tail states created by potential fluctuations.     

Synthesis and characterization of Mg2B2O5

Magnesium borate of the form Mg₂B₂O₅ has been prepared and its structural and thermal properties were studied using X-ray diffraction and differential thermal analysis. An investigation of the electrical and optical properties of Mg₂B₂O₅ system has been carried out. The electrical resistivity of the sample was measured in the temperature range of 170-400 K. The data analysis revealed an extrinsic nature of the conductivity with two impurity levels located at 0.13 and 0.71 eV in the temperature ranges of 170-230 K and 240-400 K, respectively. The optical transmission and reflection was recorded at 300 K in the incident photon energy range of 3.0-6.0 eV. The absorption coefficient data analysis revealed an indirect optical energy band gap of 4.73 eV. In addition, two impurity levels located at 3.43, and 4.49 eV were observed in the absorption spectra.     

Z-scan measurement for the nonlinear absorption of Bi2.55La0.45TiNbO9 thin films

Bi_2.55La_0.45TiNbO₉ (BLTN-0.45) thin films with layered aurivillius structure were fabricated on fused silica substrates by pulsed laser deposition technique. Their structure, fundamental optical constants, and nonlinear absorption characteristics have been studied. The film exhibits a high transmittance (> 60%) in visible-infrared region. The optical band gap energy was found to be 3.44 eV. The optical constant and thickness of the films were characterized using spectroscopic ellipsometric (SE) method. The nonlinear optical absorption properties of the films were investigated by the single-beam Z-scan method at a wavelength of 800 nm laser with a duration of 80 fs. We obtained the nonlinear absorption coefficient β = 4.64 × 10^− 8 m/W. The results show that the BLTN-0.45 thin film is a promising material for applications in absorbing-type optical device.     

Structural,optical and electrical properties of In4Sn3O12 films prepared by pulsed laser deposition

Highly conducting (σ ∼ 2.6 × 10³ Ω⁻¹ cm⁻¹) In₄Sn₃O₁₂ films have been deposited using pulsed laser deposition (PLD) on glass and quartz substrates held at temperatures between 350 and 550 °C under chamber pressures of between 2.5 and 15 mTorr O₂. The crystallinity and the surface roughness of the films were found to increase with increasing substrate temperature. Electron concentrations of the order of 5 × 10²⁰ cm⁻³ and mobilities as high as 30 cm² V⁻¹ s⁻¹ were determined from Hall effect measurements performed on the films. Fitting of the transmission spectral profiles in the ultra-violet–visible spectrum has allowed the determination of the refractive index and extinction coefficient for the films. A red-shift in the frequency of plasmon resonance is observed with both increasing substrate temperature and oxygen pressure. Effective masses have been derived from the plasma frequencies and have been found to increase with carrier concentration indicating a non-parabolic conduction band in the material In₄Sn₃O₁₂. The optical band-gap has been determined as 3.8 eV from the analysis of the absorption edge in the UV. These results highlight the potential of these films as lower In-content functional transparent conducting materials.     

Structural and optical studies of ZnS nanocrystal films prepared by sulfosalicylic acid (C7H6O6S)-assisted galvanostatic deposition with subsequent annealing

Zinc sulfide (ZnS) semiconductor nanocrystal films have been prepared on indium tin oxide coated glass substrates by sulfosalicylic acid (C₇H₆O₆S)-assisted galvanostatic deposition with subsequent annealing. The deposition was performed at 10 mA cm^− 2 in acidic electrolytes containing 15-30 mM Zn(CH₃COO)₂, 20 mM Na₂S₂O₃, 200 mM LiCl, 0.375 mM Na₂SO₃, and 0 or 0.2 mM C₇H₆O₆S. Results show that the presence of C₇H₆O₆S can suppress the precipitation of Zn and S impurity phases during the ZnS deposition process. As the [C₇H₆O₆S] = 0.2 mM and [Zn^2 +] = 20 mM, the deposited ZnS film exhibits only hexagonal structure with an ideal Zn/S atomic ratio of 1.03 and a close-packed granular morphology. But its band gap about 2.86 eV is narrower than the common value of ZnS, probably due to the existence of some spurious acetate species and defect states. By annealing the film at 400 °C for 60 min, its band gap increased up to 3.70 eV, despite that its crystalline phase transformed into cubic structure which usually shows the narrower band gap than hexagonal ZnS. The significant band gap widening could be ascribed to the degradation of spurious acetate species and the reduction of various possible defect states in the annealing process.