ZnSe Films Research Articles

Theoretical DFT and experimental investigation of the effect of Co doping in electrochemically deposited ZnSe films

In this study, we examine the impact of introducing cobalt doping on the morphological, structural, optical, and electronic properties of ZnSe thin films produced by electrodeposition at room temperature. Characterization techniques, including X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and UV–Vis–NIR spectroscopy, were employed to analyze structural, morphological, and optical features. The developed films display a consistent and even distribution of grains with a cubic structure, showcasing a preferred orientation along the (111) axis. The calculated crystal size was estimated to be around 80 nm. The elemental composition of the film aligns with the synthesized deposition of elements. The introduction of cobalt resulted in enhanced optical properties and reduced energy bandgaps in the films. Concurrently, theoretical studies using the FP-LAPW approach in density functional theory were conducted, focusing on structural, electronic, and optical properties of cobalt-doped ZnSe at different concentrations (2 %, 4 %, 6 %). Theoretical findings demonstrated a substantial decrease in the bandgap, aligning well with the experimentally determined value of 2.72 eV. This coherence between theoretical predictions and experimental observations highlights the effectiveness of cobalt doping in influencing the optical characteristics of ZnSe thin films.

Bi2Se3/ZnSe heterojunction on flexible Mo metal foil for photo electrolysis water splitting application

Abstract The green hydrogen generation by photoelectrochemical (PEC) process emerged as a viable approach to replace non-renewable energy sources, which is done by using semiconducting materials. Recently ZnSe-based heterostructure/junction promise a suitable approach to enhance the PEC performance of photoelectrode. Here we have grown Bi2Se3/ZnSe heterojunction on flexible Mo metal foil by using magnetron sputtering technique toward PEC water splitting application. The crystallinity, structural, and surface morphology of the deposited films were investigated by X-ray diffraction, Raman spectroscopy, and field emission scanning electron microscopy, respectively. The PEC measurements were performed under 100 mW/cm2 (AM = 1.5 G) simulated solar radiation in 0.5 M Na2SO4 aqueous electrolyte solution. The PEC measurements show that Bi2Se3/ZnSe photoelectrode performs better as a photocatalyst, with a photocurrent density of ∼96.4 μA/cm2 (at 0.4 V vs Ag/AgCl), which was found to be three times higher than pristine ZnSe film (∼32.4 μA/cm2). This work suggests the importance of heterojunction towards efficient photoelectrodes for green hydrogen generation.

A Comprehensive Study on Structural and Optical Properties of Zinc Selenide/Poly Ortho-methoxyaniline Hybrid Thin Films Deposited by Chemical Bath Deposition and Plasma Polymerization Techniques

Hybrid thin films hold dominant importance in various technological applications due to their synergistic effects between inorganic and organic materials. In this study, inorganic–organic hybrid thin film has been produced where the inorganic layer of zinc selenide (ZnSe) is deposited first through chemical bath deposition technique and the organic layer is deposited onto the inorganic layer using a capacitively coupled plasma polymerization technique. The ZnSe layer deposited for one hour has been used as the base layer and plasma polymerized (PP) o-methoxyaniline (OMA) has been deposited for different deposition durations. The experimental results showed that thickness of the the hybrid films increases with the organic layer deposition time. The field emission scanning electron microscope exhibited a large number of pores on the surface of the ZnSe film, which are significantly covered up when organic PPOMA is deposited onto it. The energy-dispersive X-ray confirms the constitutional elements of the hybrid films and X-ray diffraction study indicates the enhancement of crystallinity of the film. Differential scanning calorimetry and thermogravimetric analysis specify that hybrid films are thermally more stable (up to 396 °C) compared to pure ZnSe film (351 °C), probably due to higher conjugation in the PP organic layer. The direct optical band gaps of the deposited hybrid thin films are found to increase from 2.4 to 2.80 eV with the increase of organic layer onto ZnSe film. Consequently, the Urbach energy decreases from 0.94 to 0.66 eV with the deposition of hybrid film for different time durations. The outcomes of this study suggest that the hybrid films would have enormous potential as passive thin films for photovoltaic cells, sensing and optical devices.

Comparative Assessment of Optical and Solid-State Characteristics in Antimony-Doped Chalcogenide Thin Films of ZnSe and PbSe to Boost Photovoltaic Performance in Solar Cells

Solar cell efficiency is crucial for maximizing the potential of solar energy as a sustainable power source. This research investigates the optical and solid-state properties of antimony-doped ZnSe and PbSe thin films using the spray pyrolysis technique. The process involves meticulous cleaning of soda-lime glass substrates, deposition of precursors (antimony chloride (SbCl3), lead chloride (PbCl2), hydrated zinc acetate (Zn (CH3COO) •3H2O), and sodium selenosulfide (NaSeSO3) via nebulizer-driven atomization onto heated substrates at a temperature of 80°C, and subsequent annealing at 300°C in a controlled nitrogen atmosphere for 60 minutes, facilitated by a tube furnace. Optical property evaluation through UV-Vis spectrophotometry reveals intriguing trends, such as a decrease in absorbance and an ascending transmittance with elongated wavelengths. Annealed films exhibit peak optical conductivity values around the visible spectrum, and augmented refractive indices correlate with increased wavelengths, further enhanced through annealing. Antimony doping influences band gap energy, making these materials promising for solar cell fabrication. This study underscores the potential of antimony-doped ZnSe and PbSe thin films to enhance solar cell efficiency. The films offer features like enhanced light trapping, lowered band gap energy, and improved charge transport characteristics, making them suitable for various solar cell applications, including antireflection coatings and light-trapping layers. Continued exploration and refinement of these materials are anticipated to lead to novel advancements in solar cell design and manufacturing, contributing to more efficient and impactful energy conversion techniques.

Realization temperature roles of in-situ ZnSe films growth toward efficient photodetection performance

The optoelectronic properties of most of the chalcogenide thin film can be manipulated by precise control of the preparation conditions specifically the substrate temperature during deposition. Therefore, our investigation focused on examining the impact of varying substrate temperatures (27 - 250 °C) on the structural, optical, and electrical properties of vacuum-deposited zinc selenide thin films. The improvement of the films’ structural properties was demonstrated through a series of systematic investigations utilizing various techniques including X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), and field emission scanning electron microscopy (FE-SEM) in conjunction with energy-dispersive X-ray spectroscopy (EDAX) unit. The findings were presented in a systematic and comprehensible manner, supported by the shown surface changes accompanied by the stoichiometrical ratio between zinc and selenium ratios up to a temperature of 150 °C. The observed crystal/grain growth behavior up to 150 °C improved the optical dispersion parameters, and enlarged energy gap values, which was also electrically reflected in the improved electrical conductivity of films from 3.48 × 10−8 to 1.47 × 10−7 Ω−1.cm−1. In turn, the electrical properties of a heterojunction of ZnSe films prepared at different temperatures with CdTe have been studied, and likewise, the junction that comprises ZnSe film deposited at Ts =150 °C has been surpassed. The evaluated photodetection behavior of the designed heterojunction device showed high performance under varying illumination intensity and wavelength with responsivity, detectivity, and external efficiency of about 104 mA/W, 5.41 × 1010 Jones, and 30.7%, respectively. The comparison between the present device's performance and other previous devices suggests this device is for high-performance, efficient dual-band photodetection applications.

From non-stoichiometric CTSe to single phase and stoichiometric CZTSe films by annealing under Sn+Se atmosphere

One of the new materials for next-generation thin film solar cells is Cu2ZnSnSe4 (CZTSe). However, achieving a single-phase CZTSe compound remains a challenge. This study describes the development of Cu2ZnSnSe4 thin films through the sequential deposition of stacked films of non-stoichiometric Cu2SnSe3 (CTSe) and ZnSe by magnetron sputtering. The structural, morphological, and electrical properties as well as the surface chemistry of the films were investigated and compared depending on the growth sequence of the thin films. By using Raman spectroscopy and grazing incidence X-ray diffraction, the tetragonal CZTSe structure was confirmed. Scanning electron microscopy and energy-dispersive spectroscopy measurements of the morphological and compositional properties indicated large grains and dense surfaces with an elemental composition close to the desired stoichiometry in SLG\\SnSe2\\Cu\\ZnSe and SLG\\SnSe2\\Cu2Se\\ZnSe stacks. To ascertain the surface chemistry and unique characteristics of the produced films, additional X-ray photoemission spectroscopy experiments were carried out. The optimal band gap values for the absorber layers were found using conventional spectroscopy, and they ranged from 0.88 to 1.47 eV. According to the electrical measurements, all the films were p-type and have high carrier concentrations between 1016 and 1020 cm−3. Our findings demonstrate that employing a sequential deposition approach and annealing in different atmospheres can yield CZTSe absorber layers with desirable properties, overcoming the challenge of non-stoichiometric CTSe precursors.

Analysis of surface properties of Mg doped ZnS and ZnSe thin films through x-ray photoelectron spectroscopy

The surface properties of the spray-deposited Mg-doped ZnS and ZnSe films were investigated using X-ray photoelectron spectroscopy (XPS). The energy levels of the core electrons in ZnMgS and ZnMgSe, their peak positions, area ratios, and full width at half maximum were determined. Chemical shifts in Auger peaks, which are highly sensitive to changes in the chemical environment were used in the analysis. Compositional analysis indicated selenium deficiency in the ZnMgSe films. XPS peak of magnesium 2p showed a shift from 50.46 eV for ZnMgSe film to 50.63 eV for ZnMgS film and Mg 2s peak shift from 86.56 eV for ZnMgSe to 87.64 eV for ZnMgS films. A careful justification for the formation of oxides in the ZnMgSe films is also given. Ionicity for both films is about 0.51. Peak shifts in the Auger and core-level peaks are used to analyze the material's bonding strength, oxidation states, and bonding types.

Design, Preparation and Characterization of Mid-infrared Low-emissivity Film

The rapid development of infrared detection technology requires that military targets have mid-infrared stealth performance. In this paper, a mid-infrared low-emissivity film based on one-dimensional photonic crystal structure was designed and prepared. The results showed that its reflectivity properties are improved and total thickness is reduced by optimizing the construction parameters. The thickness and refractive index of the prepared Ge film and ZnSe film were tested using IR ellipsometer. After the test results were brought into the designed structure, mid-infrared low-emissivity films with emissivity of 0.032, 0.068, 0.146, 0.203 and 0.366 were prepared by vacuum evaporation. The infrared reflectivity of the mid-infrared low-emissivity films was tested using Fourier spectrometer, and the test results are in good agreement with calculated results.

Multi-wavelength passively Q-switched laser with Co2+:ZnSe thin film coated microsphere

We experimentally demonstrate an all-fiber passively Q-switched erbium-doped laser based on a microsphere resonator coated with Co2+:ZnSe film, which can achieve multi-wavelength pulse laser. With electron beam evaporation technology, the saturable absorber (SA) with a modulation depth of 55% was prepared by depositing Co2+:ZnSe film on the microsphere for the loss modulation of the laser cavity. The passively Q-switched output pulses were obtained by inserting the SA into the laser cavity and the narrowest pulse width of ∼3 μs was obtained. The fiber laser can stably output quintuple-wavelength laser pulses with a 3 dB bandwidth of ∼0.1 nm. The wavelength interval of multi-wavelengths was stably maintained at ∼1 nm and the smallest optical signal-to-noise ratio of ∼10 dB at the pump power of 400 mW was measured. The signal-to-noise ratio was ∼58 dB, which confirms excellent output stability. The results prove that it is a promising SA device to achieve passively Q-switched multi-wavelength pulse fiber lasers.

Study of Optical and Electrical Properties of RF-Sputtered ZnSe/ZnTe Heterojunctions for Sensing Applications

Cadmium (Cd)-free photodiodes based on n-type Zinc Selenide/p-type Zinc Telluride (n-ZnSe/p-ZnTe) heterojunctions were prepared by Radio Frequency-Magnetron Sputtering (RF-MS) technique, and their detailed optical and electrical characterization was performed. Onto an optical glass substrate, 100 nm gold (Au) thin film was deposited by Thermal Vacuum Evaporation (TVE) representing the back-contact, followed by the successive RF-MS deposition of ZnTe, ZnSe, Zinc Oxide (ZnO) and Indium Tin Oxide (ITO) thin films, finally resulting in the Au/ZnTe/ZnSe/ZnO/ITO sub-micrometric “substrate”-type configuration. Next, the optical characterization by Ultraviolet-Visible (UV-VIS) spectroscopy was performed on the component thin films, and their optical band gap values were determined. The electrical measurements in the dark and under illumination at different light intensities were subsequently performed. The Current–Voltage (I–V) characteristics in the dark are nonlinear with a relatively high asymmetry, following the modified Shockley–Read equation. From their analysis, the series resistance, shunt resistance, the ideality factor and saturation current were determined with high accuracy. It is worth noting that the action spectrum of the structure is shifted to short wavelengths. A sensibility test for the 420–500 nm range was performed while changing the intensity of the incident light from 100 mW/cm2 down to 10 mW/cm2 and measuring the photocurrent. The obtained results provided sufficient information to consider the present sub-micrometric photodiodes based on n-ZnSe/p-ZnTe heterojunctions to be more suitable for the UV domain, demonstrating their potential for integration within UV photodetectors relying on environmentally-friendly materials.

Fabrication and characterization of ZnS and ZnSe absorber layers for UV-selective transparent photovoltaics

We have fabricated ZnS, ZnSe and mixed Zn(S,Se) thin film layers for application as solar cell absorbers in ultraviolet (UV)-selective solar cells. We fabricated the thin film layers using a two-step process involving evaporation of the Zn layer followed by an anneal in an H2S and/or H2Se containing atmosphere. A study of the annealing conditions was performed to minimize hole formation in the thin film layer. A mixed Sulfur and Selenium containing layer was also developed in order to reach a 3 eV band gap, such that the layer absorbs all the UV light and leaves the visible light passing through. Next, we tried to increase the conductivity of the layer by adding extrinsic doping elements. Cu was found to increase the conductivity by more than three orders of magnitude, while leaving the transparency of the layer mostly unchanged. Finally, solar cell devices were fabricated using transparent back and front contacts and a NiO buffer layer. We could measure a very small photocurrent of about 100 μA/cm2 and an open circuit voltage of about 500 mV under AM1.5 G illumination.

Investigation of porous ZnSe thin films prepared by thermal evaporation

ZnSe films with thickness of 50, 70 and 100 nm were prepared on Corning 7059 glass substrates at room temperature by applying continuous or periodically interrupted physical vapour deposition at very low deposition rates (0.2 and 0.5 nm s−1). Part of the films was annealed at 200 °C after deposition. Optical absorption spectra determined from spectroscopic ellipsometry data show direct allowed transitions, which indicate that the films have microcrystalline structure. This is in agreement with scanning electron microscopy and atomic force microscopy results. The spectroscopic ellipsometry results also show that the porosity of the films is strongly affected by both manner of deposition and deposition rate; the annealing causes some porosity decrease. Optical transmission spectra reveal that the transmittance of as-deposited films, obtained by periodically interrupted manner is significantly influenced by their porosity.

Transfer matrix method for calculating UV–Vis reflectivity/transmission spectra to assess thickness of nanostructured zb CdSe and ZnSe films grown on GaAs (001)

Transfer matrix method for calculating UV–Vis reflectivity/transmission spectra to assess thickness of nanostructured zb CdSe and ZnSe films grown on GaAs (001)

Effect of indium doping on the optoelectronic properties of ZnSe films

Polycrystalline In:ZnSe films were prepared by the thermal co-evaporation method, where high purity ZnSe and In2Se3 powders are taken as source materials. Orderly change in the X-ray diffraction peak position and red shift in the optical absorption edge have confirmed the incorporation of the dopant in the system. Photoluminescence spectra showed that the doped system has a Zn vacancy, which is in line with energy dispersive spectroscopy measurements. The chemical state of the doped films i.e., Zn2+, In3+ and Se2− was analysed by Raman and X-ray photoelectron spectroscopy (XPS); XPS has also indicated the incorporation of oxygen in small fractions which improves the conductivity of the films. The electrical investigation has revealed that electrical properties altered by doping and majority charge carriers are electrons and carrier density is in the order of 1015 cm−3. Films with 15 at. % In exhibited good photoresponse in the visible range and suitable for photodetector applications.

Effects of SeO2 epilayer on the structural, morphological, optical and dielectric properties of nanocrystalline ZnSe thin films

Herein the effects of SeO2 coating on the physical properties of thermally evaporated nanocrystalline (NC) ZnSe thin film substrates are explored. The formed ZnSe films showed nanocrystalline Zincblende phase. They contained excess selenium (ZnSe1.07) with relatively large defect density and displayed band gap of value of 3.48 eV, energy band tails of width of 1.2 eV and dielectric quality factor (Q) less than 100. Coating NC-ZnSe with SeO2 induced the crystallization of tetragonal SeO2 and enhanced the light absorbability of SeO2. It also reduced the defect density and stacking faults, increased the crystallites sizes, narrowed the width of band tails, increased the dielectric constant and increase the Q factor up to ∼400 of NC-ZnSe. In addition, analysis of the optical conductivity spectra for the NC-ZnSe/SeO2 bilayers has shown that the drift mobility, plasmon frequency and free carrier density can reach values of 30.42 cm2/Vs, 5.07 GHz and 8.0 ×1018 cm−3, respectively.

Guided-mode resonance with reduced bandwidth in mid-infrared absorption and thermal emission.

Narrowband resonance plays an important role in many optical applications, especially for the development of wavelength-selective properties and enhanced light-matter interaction. In this paper, we demonstrate metal-insulator-metal (MIM) waveguide gratings, which exhibit guided-mode resonance (GMR) with reduced bandwidth in mid-infrared absorption and thermal emission. Our fabricated MIM waveguide grating consists of a copper substrate, a lossless ZnSe film, and a top gold stripe grating. Our measurements reveal strong GMRs with a bandwidth of 1.29% of the central wavelength in both mid-infrared absorption and thermal emission spectra. By varying structural parameters of the MIM waveguide grating, strong absorptions and thermal emissions of GMRs are observed and tuned within the 3-5 µm wavelength range. These results manifest the great potential of engineering infrared properties by using GMR and could be useful for spectral control in a variety of infrared devices.

ZnSxSe1−x thin films: A study into its tunable energy band gap property using an experimental and theoretical approach

In recent times, ZnS and ZnSe thin films are drawing tremendous attention towards opto-electrical devices due to their optimal wide band gap energy. By alloying ZnS and ZnSe films to obtain ZnSxSe1−x thin films, the band gap of the ZnSxSe1−x film can be tuned to a value according to the device requirements. Herein, ZnSxSe1−x thin films were deposited on pre-cleaned glass substrates using a thermal evaporation system and the various properties of the obtained thin films were analyzed by altering the percentage of sulfur concentration in the films. The XRD analysis illustrated that the prepared films are polycrystalline in nature and oriented along cubic (111) plane. The deviation of (111) preferential peak position with composition ‘x’ along the absence of any secondary peaks confirms the formation of ternary ZnSxSe1−x thin films. DFT analysis verifies the formation of pristine ZnSxSe1−x alloy system. FESEM micrographs displayed that the ZnSxSe1−x thin films do not have any cracks or pinholes. EDAX analysis of the films revealed the existence of Zn, Se and S in an appropriate quantity. Optical analysis revealed the effective band gap tailoring of ZnSxSe1−x thin films. The band gap of the ZnSxSe1−x thin films increases from 2.59 eV to 3.38 eV as the composition ‘x’ varied from 0 to 1 and band composition was determined using the DOS plot obtained using VASP.

Photo-resistor applications of Bi:ZnSe nano-composition deposited on micro-glass

Bi:ZnSe films at different concentrations (0, 5, 10, and 15%) were made by the laser deposition technique. The scanning electron microscopy and Uv–visible spectroscopy were used to investigate the surface topography and optical properties of the prepared films, respectively. The calculated energy gap was (3.0, 2.6, 3.2, and 3.1 eV) due to differences in lattice parameters. Moreover, the electrical characteristics reveal enhanced dark current with all samples probably due to the essential property of p-type doped ZnSe Nano-composition. The density, refractive index, permittivity, and reflection loss were also studied versus Bi-dopant. The structural characteristics of the coated films have been tested by an X-ray diffractometer. In addition, the interstitial or substitutional Zn ion by Bi ion in the lattice was also explained in this paper.

Demultiplexers for DWDM applications using one-dimensional planar binary photonic crystals defected with ZnSxSe1-x ternary alloys

We propose a structure comprising a defective one-dimensional planar binary photonic crystal (PC) to realize a demultiplexing operation for dense wavelength division multiplexer (DWDM) transmission systems. The unit cell of the crystal consists of ZnSe and ZnS thin films, and the defective layer is ZnSxSe1 − x, (0 ≤ x ≤ 1). Transmittance for the structure was numerically investigated using the transfer matrix method. The selecting mechanism of the output wavelength was based on selecting the appropriate sulfur concentration (x value) in the defective layer of the PC. We used six different sulfur concentrations to demultiplex six different output channels. The line width of the output channels was about 0.13 nm with a quality factor of 12,199. The average crosstalk between the adjacent transmitted channels was about −22.16 dB. The overall dimension of the proposed demultiplexer was about 108.4 μm, which practically makes the demultiplexer easily integrated into photonic circuits. Our results show that the proposed structure has all of the required characteristics to demultiplex the C-band signals with a 0.16 nm separation, which corresponds to the ITU grid for DWDM.

Change in structure and luminescent properties of ZnSe and ZnCdSe films irradiated by electron beam

Layers of ZnSe and ZnCdxSe (x ~ 0.32-0.35) grown on GaAs (001) substrates by molecular beam epitaxy method were investigated. The electron beam impact on changes in crystal structure of specimens under examination and on their luminescent properties was studied. Methods of cathode luminescence, transmission electron microscopy, and electron microprobe analysis were applied. It is found that irradiation of specimens in the transmission electron microscope results in stacking faults annealing accompanied by formation of ZnO precipitates with hexagonal crystal structure. Irradiation of specimens in the cathode luminescence plant results in decreased intensity of cathode luminescence layers of ZnSe and ZnCdxSe in question due to radiation-stimulated degradation processes. Key words: point defects, irradiation by electron beam, cathode luminescence, structural changes.