CdSe Thin Films Research Articles

Characterization of chemically deposited nanocrystalline CdSe thin films from transmittance spectra

Optical properties of nanocrystalline films of CdSe prepared by chemical bath deposition technique are studied as a function of molar concentration. Analyses of the transmittance spectra over 350–900 nm photon wavelengths of CdSe films indicates the existence of direct optical transition. A blue shift of absorption edge was observed which indicates a decrease in crystallite size. The optical band gap (Eg) was found to be in the range of 1.93–2.10 eV for as-prepared films. After annealing the band gap was found to decrease. The crystallite size was found in the range of 3.34–4.99 nm using the effective mass approximation model. Different optical parameters such as absorption coefficient, refractive index, extinction coefficient, optical conductivity, dielectric constants were determined from the transmittance spectra.

Tailoring the CdS/CdSe/CdTe multilayer structure for optimization of photovoltaic device performance guided by mapping spectroscopic ellipsometry

Thin film CdTe superstrate solar cells have been fabricated by sputtering starting from CdS/CdSe front layers deposited on transparent conductor coated glass. The performance of such devices is sensitive to the fabrication details including the temperature-time profile, which leads to CdSe/CdTe interdiffusion and formation of a CdTe1-xSex bandgap-graded absorber. Mapping spectroscopic ellipsometry (M-SE) has been applied to the CdS and CdSe thin films for process calibration, which involves determining the deposition rate in terms of effective thickness (volume/area) versus spatial position on the sample. The goal is to optimize the performance of the devices by correlating cell parameters with these two effective thicknesses. Intended variations in the thicknesses along with unintended spatial non-uniformities enable coarse and fine-scale optimization, respectively. Using these methods, the highest performance solar cells from the CdS/CdSe/CdTe structure are obtained with 13 nm CdS and 100 nm CdSe. An increase in the CdS thickness above 13 nm leads to a decrease in open-circuit voltage and fill-factor attributed to the formation of a CdSe1-zSz interdiffusion region with z approaching 0.5, where the alloy electronic properties are likely to suffer. Our results demonstrate that M-SE, exploited in conjunction with deposition non-uniformities, serve as a viable approach for process optimization of complex solar cell structures.

Superior electrochemical activity of CdSe thin film by chromium substitutional doping

Substitutional doping is the prominent way to modify the photoanode of the photoelectrochemical system by which its response to solar spectrum can be manipulated. Here, we introducing the transition metal Cr into the CdSe host lattice to investigate the photoelectrochemical (PEC) performance. The Cr doped CdSe thins films were deposited by periodic cyclic voltammetry method. XRD and Raman spectroscopy confirm the cubic phase of all grown films with the good substitution of Cr3+ is on Cd2+ lattice site in CdSe host lattice. Surface morphology and compositional conformation were studied by SEM and EDAX. Transmission electron microscopy shows the good polycrystalline nature of all deposited samples. The Cr substitution in CdSe host lattice enhances the visible light absorption due to an increase in the specific surface area of the film. The photoelectrochemical (PEC) performance was investigated using the three-electrode system which reveals that the optimum level doping (0.2 M) of Cr into CdSe enhances the photocurrent density and responsivity by ~3 times in comparison to pure CdSe thin film. Our results confirmed that Cr is the attractive dopant to modify the photoelectrochemical activity of the CdSe thin film.

A dynamic optical constant extraction method for thin films with structural and optical-parametric justifications

An original fitting approach grounded on dynamic n(λ) dispersion along with envelop based Connell–Lewis (C–L) relation for optical absorption was developed and implemented to extract the optical constants from experimental T(λ) spectra of thin films. Thermal-vapor-deposited chalcogenide CdSe thin films having a thickness range of ∼650–1550 nm were chosen for this purpose. The interdependence of n(λ) and k(λ) in the analytical T(λ) expression through the C–L equation partially mimics the Kramers–Kronig relation, which is a requirement for the optical constant to be physically meaningful. The average quadratic function within the measured spectral range was found to fall below 1%. On the contrary, a pronounced scattering in the relative difference spectra (∼10%) observed within a very narrow band of interference pattern was attributed to a systematic error and uncertainty in the spectral shape just above the absorption edge. The validity of the extracted optical and dimensional parameters was scrutinized in terms of microstructural and crystallographic measurements. The variation in packing density, estimated from the extracted n(λ) spectra, commensurates with the temperature evolution of microstructural features. The bathochromic shifts in the split transition energies obtained from the extracted k(λ) spectra were discussed satisfactorily in terms of the quantum threshold size effect. Although this fitting approach was applied only to a chalcogenide thin film, it is anticipated to be applicable to the other transparent thin films as well.

Temperature effects on optical characteristics of CdSe thin films

CdSe is one of the significant members of II-VI type semiconducting family and it has a wide range of technological applications in which optoelectronic devices take a special position. The present paper reports the structural and optical characteristics of thermally evaporated CdSe thin films. XRD pattern exhibited preferential orientation along (111) plane while atomic composition analyses resulted in the ratio of Cd/Se as closer to 1.0. Temperature-dependent band gap characteristics of CdSe thin films were investigated for the first time by carrying out transmission experiments in the 10–300 K range. The analyses showed that direct band gap energy of the compound decreases from 1.750 (at 10 K) to 1.705 eV (at 300 K). Varshni model was successfully applied to the temperature-band gap energy dependency and various optical constants were determined. Raman spectrum of CdSe thin films was also presented to understand the vibrational characteristics of the compound. The present paper would provide worthwhile data to researchers especially studying on optoelectronic device applications of CdSe thin films.

Annealing temperature assisted microstructural and optoelectrical properties of CdSe thin film grown by RF magnetron sputtering

Abstract Cadmium selenide (CdSe) thin films are widely used in electronic devices as well as a potential window material in solar cell applications. In this study, 100 nm CdSe thin films were grown on borosilicate glass substrates by using Radio Frequency (RF) magnetron sputtering technique at room temperature (25 °C). Deposited films were annealed in a vacuum furnace at 100 °C, 200 °C, 300 °C, 400 °C and 500 °C for 10 min, respectively. In-depth analysis of the microstructural and optoelectrical properties of annealed films were performed using X-ray diffraction (XRD), UV–Vis spectrometry and Hall Effect measurements. From XRD results, the films illustrated hexagonal structure with preferred orientation (002) at 2θ = 24.12°. UV–Vis study indicated that the transmission ranges were from 75% to over 85% for annealed samples and the calculated optical band gap was in the range 1.65 eV–1.73 eV. Optical properties demonstrated that CdSe had the potential to be incorporated as a window layer in solar cells. Meanwhile, the electrical measurements showed n-type conductivity with the carrier concentration of 1014 cm−3 for all the annealed films. The optimized results recommend sputtered CdSe thin films annealed at 400 °C as a possible window layer to the Cd-based solar cells.

CdS/CdSe HETEROSTRUCTURES GROWN BY CHEMICAL TECHNIQUES ON FLEXIBLE PET/ITO SUBSTRATES

Undoped and Mn-doped CdS films, CdSe films and CdS:Mn/CdSe heterostructures were deposited by chemical techniques. Undoped and Mn-doped CdS films were grown onto flexible PET/ITO substrates by chemical bath deposition at different temperatures. CdSe thin films were synthesized following a two stages process. In the first stage, CdO2 precursor films, were synthesized by chemical bath deposition at different deposition time. In the second stage, the CdO2 precursor films were transformed into CdSe films by immersion in a Se ionic solution. CdS, CdS:Mn, CdSe and CdS/CdSe samples were characterized by high-resolution transmission electron microscopy, UV-vis, Raman and room temperature photoluminescence spectroscopies. The structural characterization indicates that CdS and CdSe films with hexagonal phase were obtained. CdSe films showed the LO Raman mode with three order phonon replicas, an indication of the excellent crystalline quality of the samples.

Photoresponse properties of CdSe thin film photodetector

In the present investigation, the performance of highly sensitive photodetector based on CdSe thin film has been demonstrated. The cadmium selenide (CdSe) films were deposited successfully by spray pyrolysis method on glass substrate. The as-deposited films were used as visible light detector. Further, the structural, morphological, and optical properties of CdSe films were investigated through X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy, and optical absorption spectrophotometer. The XRD studies show that the produced samples are polycrystalline in nature. A UV–Visible absorbance spectrum indicates direct allowed transition with bandgap about 1.75 eV. The SEM micrographs depict uniformly distributed well defined uneven hexagonal grains. The CdSe film-based photodetector exhibits high responsivity, detectivity and shows an ultrafast photoresponse. The excellent photoresponse and high photosensitivity of CdSe film makes it a strong candidate for high-performance photodetectors.

Preparation and characterization of pulsed laser deposited CdSe window layer for Sb2Se3 thin film solar cell

Antimony selenide (Sb2Se3) is a potential photoelectric absorber for its excellent photoelectric properties, low cost and less pollution. At present, the main window layers are CdS, ZnO, TiO2 and SnO2 in Sb2Se3 solar cells, while there is a lack of research on CdSe film. Here, the CdSe films were deposited at 100 °C, 200 °C, 300 °C and 400 °C by pulsed laser deposition as the window layer of Sb2Se3 solar cell. The XRD and TC values results for CdSe/Sb2Se3 films demonstrated that CdSe films deposited at different temperatures can promote the (hk1) orientation growth of Sb2Se3 films, in which the (221) orientation of Sb2Se3 film is optimal when the CdSe film deposited at 300 °C. Scanning electron microscope results showed that the surface of the Sb2Se3 thin film with CdSe film deposited at 300 °C has relatively uniform grains. Comparing the different temperatures, the CdSe/Sb2Se3 heterojunction was obtained by deposition of CdSe thin films at 300 °C, with the highest efficiency of 3.65%. This study confirmed the feasibility of CdSe thin film as a window layer of Sb2Se3 solar cells.

Effect of Rapid Thermal Annealing on Thermal Evaporated CdSe Thin Film for Solar Cell Application

Cadmium Selenide (CdSe) thin films have been deposited on a cleaned glass substrate by thermal vacuum evaporation method under the pressure of 10-5 torr. These CdSe thin films were also kept into a quart glass tube for rapid thermal annealing at 60 and 120 second using a 500 W halogen lamp for crystalline the structure. These thin films were characterized for structural, optical and thermo-electrical properties. The optical studies have been done using UV-VIS-NIR, shows that the transition of the deposited film is found to be a direct band gap of 1.74, 1.70 and 1.67 eV for asdeposited, 60 sec and 120 sec annealed thin films respectively. It was also found that absorbance has increased and transmission decreased with increasing annealing time, the change in the extinction coefficient with energy (hν) has been also measured. The Thermoelectric power (TEP) studies confirm the n-type nature of CdSe thin films but as well as annealing time increased the hole concentration increased resultant n-nature of CdSe thin film changing toward p-type nature, the Seebeck coefficient for different annealing time at as-deposited (RT), 60 seconds and 120 seconds have observed 549, 949 and 1031 μV/K respectively. The SEM result shows that with increasing annealing time the grain size and roughness of surface are increased. X-ray diffraction (XRD) studies indicate that the film is like a cubic crystal structure with average crystalline size (D) was measured using Scherrer formula and it is 16.44 nm.

Study of the influence of synthesis conditions on stoichiometry and the properties of nanostructured CdSe thin films

The interest in thin films based on chalcogenides, among which CdSe structures stand out, is due to the great prospects for their use as various photocatalysts, microelectronic devices, etc. However, despite the large number of scientific works in the field of studying the properties of semiconductor thin films, there are still many unresolved issues. In this regard, the main goal of this work is a systematic study of the influence of electrochemical deposition conditions, in particular, in the applied potential difference, on the change in the structural and optical properties of CdSe-based thin films, as well as assessing the applicability of the obtained thin films in photocatalytic decomposition reactions of tetracycline hydrochloride. Atomic force microscopy, X-ray diffraction, energy-dispersive analysis, and UV spectroscopy were used as research methods. In the course of the study, the dependences of the change in the stoichiometry of thin films on the applied potentials difference were established, in particular, it was found that an increase in the potential difference of more than 1.5 V leads to an increase in cadmium in the structure of the films. By the method of X-ray diffraction it was found that for thin films obtained with an applied potentials difference in of 1.75–2.0 V, in addition to the main hexagonal phase of CdSe, the appearance of weak diffraction reflections characteristic of the hexagonal phase of cadmium is observed. The prospects of using synthesized thin films as photocatalysts, which showed good photocatalytic activity over time, which ranged from 50 to 70%, are shown. In this case, films with a nonstoichiometric ratio of elements have the highest photocatalytic activity.

Erratum to: Peculiarities of the Optical and Energy Properties of Thin CdSe Films

Erratum to: Peculiarities of the Optical and Energy Properties of Thin CdSe Films

Electrical, Thermoelectrical and PEC Studies of Copper Doped CdSe Thin Films

Copper doped CdSe thin films of various composition (0.1-1.0 mol %) deposited by dip coating technique on clean glass substrate at room temperature. Sample prepared on stainless steel plates have been applied for PEC characterization. The electrical conductance at 300K enhances as the amount of copper raises up to 0.1 mol % and later magnitude shrinks for greater amount.Copperr doped samples demonstrates n-kind conductance. As temperature rise conductivity also rises confirming semiconducting nature of sample. Activation energy reduces up to 0.1 mol % and enhances at higher copper amount. Thermoelectric power increases up to 0.1 mol % copper dopant sample and later decreases. The rise in thermoelectric power with rise in temperature confirming the uniform characterof the sample. The various performance parameter of PEC were examined with respect to varing dopant amount. Fill factor, ideality factor, short circuit current, open circuit voltage, and solar energy conversion enhances up to 0.1 mol% copper amount then reduces. The utility of this work is in improving the efficiency of PEC cell. The efficiency of doped sample is greater than undoped cadmium selenide.

Comment on: “Investigation the effect of Pb incorporation on the surface characterizations of electrodeposited CdSe nanostructures” [J. Alloys Compd. 817 (2020) 152711

Abstract In a recent paper [J. Alloys Compd. 817 (2020) 152711] Alasvand and Kafashan have studied the physical properties of the electrodeposited CdSe thin films. As shown in this comment, the authors have used two wrong equations to calculate the absorption coefficient, α, and refractive index, n, of the samples. Consequently, the rest of the calculated parameters based on the α and n such as optical band gap, extinction coefficient, complex dielectric constant, dissipation factor and evaluated dispersion parameters using the Wemple-DiDomenico single oscillator model and Walton-Moss model, are erroneous.

Structural properties of cadmium selenide nanowires prepared by chemical bath deposition for the electrical and photosensitive characteristics of the p-Si/CdSe heterojunction

Cadmium selenide (n-CdSe) thin films were grown on a silicon substrate with a polished surface and applied to the Schottky type device structure. The n-CdSe thin films produced depended on various deposition times at 70°C by the use of the chemical bath deposition technique. XRD results show that the fabricated thin films consist of both cubic and hexagonal crystal systems. The morphology of CdSe was formed in nanograins and nanowire structures with respect to deposition times of 6 and 10 h, respectively. In addition to structural analysis of CdSe thin films, CdSe nanowires were used as an interfacial layer in a metal–semiconductor device to investigate its effects on the electrical and photosensitive characteristics of the device. As well as under forward bias current–voltage (I − V) conditions, the space charge limited current conduction behaviors were identified at low voltages. The results showed that the film produced at 10 h has a better performance compared to that produced at 6 h in terms of increased electric current.

Optical-energy properties of CdSe thin film

The optical constants and thickness of CdSe thin films prepared by quasi close-space sublimation method are determined. The structural investigations performed by means of XRD technique showed that the films have a polycrystalline and hexagonal structure. The optical constants and the band gap of the films under study have been determined (Eg= 1.68 eV). Optical properties (refractive index n(λ), absorption coefficient α(λ), and extinction coefficient k(λ)) of thin films and thickness d can be determined from the transmission spectrum. The dispersion of the refractive index was explained using a single oscillator model. Single oscillator energy and dispersion energy are obtained from fitting. Optical parameters of the films were determined using the Cauchy, Sellmeier and Wemple models.

Semi-transparent Schottky junction solar cell based on evaporated CdSe thin films: Influence of post-deposition air-annealing

FTO/CdSe/Al semi-transparent Schottky junction solar cells were fabricated by evaporating 300 nm CdSe thin films onto the FTO electrode and forming the Schottky junction by evaporation the aluminum onto the absorber layer. The performance of the samples was optimized by air-annealing the absorber layer prior to the evaporating of the top electrode. Also, the structural, optical and electrical properties of thermally evaporated CdSe thin films were investigated as a function of post-deposition air-annealing temperature. The surface morphology of the specimens was studied using field emission scanning electron microscope (FE-SEM) analysis. X-ray diffraction (XRD) analysis revealed the hexagonal structure of the samples. The crystallite size, micro-strain and dislocation density of CdSe thin films were evaluated using XRD patterns. The transmittance spectra in the wavelength range of 400−2500 nm were measured and then used to study other optical parameters. The optical energy band gap was decreased with air-annealing from 2.17 eV to 1.69 eV. It is observed that complex refractive index, relative density, complex dielectric constant and electrical polarizability of specimens were increased by air-annealing. Electrical conductivity and the photovoltaic efficiency of FTO/CdSe/Al Schottky barrier devices were improved by thermal annealing and annealed sample at 300 °C shows the best performance (η = 1.53 %). Obtained results show that CdSe thin films are a promising candidate to use as an absorber layer in semi-transparent solar cells and colorful photovoltaic windows.

Surface Deformation of Cadmium Selenide Thin Films By DEHI Technique

Abstract Here, the Double Exposure Holographic Interferometry (DEHI) technique is used to study the surface deformation of CdSe films electrodeposited on stainless steel substrate. The electrodeposition of CdSe thin films is carried out by varying the time of deposition. The deposition potential of the compound was studied by cyclic voltammetry. The structural, surface morphological and optical properties of the deposited films have been studied by X-ray diffraction (XRD), scanning electron microscope (SEM) and optical absorption technique respectively. Also the contact angle measurements are carried out. The DEHI technique is used to determine, thickness of thin films, mass deposited, fringe width and stress to substrate of electrodeposited CdSe thin films for various deposition time with different solution concentrations. With increasing deposition time fringe width was decreased due to the reduction in film stress

Peculiarities of the Optical and Energy Properties of Thin CdSe Films

The results of experimental and theoretical studies of the optical and energy properties of thin CdSe films obtained by the quasi-closed volume method are presented. The synthesis methodology and the results of structural and optical studies of thin CdSe films deposited on the surface of a quartz substrate of brand KV (GOST (State Standard) 15130-86) are given. The quality of the films is analyzed using the X-ray diffraction, energy dispersive analysis, and scanning electron microscopy techniques. Using the pseudopotential method, the dynamics of changes in the parameters of the electronic subsystem of a CdSe film is theoretically studied. The direct-gap nature of the energy gap of the film is established. Based on the density of states, the genesis of the conduction and valence bands is established. Using the Kramers–Kronig relations, we obtained the spectra of optical dielectric functions and the reflectance, refractive index, and extinction spectra, which satisfactorily correlate with the obtained experimental data.

Structural, Optoelectronic, and Photoelectrochemical Investigation of CdSe NC's Prepared by Hot Injection Method

In this study, we report the synthesis and characterization of CdSe nanocrystals (NC's) by facile Hot injection (HI) method. The formation of CdSe NC's was confirmed by x-ray diffraction (XRD), Raman spectroscopy, and x-ray photoelectron spectroscopy (XPS). The optical properties were analyzed by UV-visible and photoluminescence (PL) spectroscopy shows an excitonic peak at 600 nm in UV-Vis spectra corresponds to the band gap of ~ 2 eV favorable for optoelectronic device applications. The Photoelectrochemical (PEC) performance of CdSe thin film prepared by spin coating demonstrates a rise of photocurrent density (Jsc = 0.081 µAcm-2) after illumination. The Mott-Schottky (MS) and electrochemical impedance spectroscopy (EIS) measurements were further carried out to understand intrinsic properties namely the type of conductivity, flat band potential, charge carrier density (ND), charge transfer resistance, and recombination lifetime. The n-type conductivity, the charge carrier density of ND = 1.292 x 1016 cm-2, and recombination lifetime of 32.4 µs suggest the ideal behavior of CdSe NC's for device quality photoelectrodes.