Nanocrystalline ZnS Thin Films Research Articles

Fabrication of low-cost and fast-response visible photodetector based on ZnS:Mn/p-Si heterojunction

Present communication reports fabrication of visible sensor based on ZnS:Mn/p-Si heterostructure. Herein, Pure and Mn+2 doped ZnS nanocrystalline thin films structures have been deposited on the p-type silicon (Si) substrates using chemical bath deposition technique. The structural, morphological, and optical analysis have been systematically examined using X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet–visible (UV-VIS) and photoluminescence (PL) spectroscopy respectively. Further, the use of the deposited ZnS structures for optical and electrochemical applications was studied using Commission International DeI’Eclairage (CIE) and electrochemical analysis. The electrical properties of the fabricated ZnS:Mn/p-Si heterostructures were explored by illumination visible light of intensity 30 mW/cm2 and calculated all the essential photodetection parameters using the current-voltage (I–V) and current-time (I-T) plots. Enhanced sensitivity (5.01×102), responsivity (7.9 ×10−2 mA/Watt), linear dynamic range (54.03 dB) and external quantum efficiency (16.32%) was observed in ZnS:Mn/p-Si heterostructure device as compared to ZnS/p-Si heterostructure. Hence, the ZnS:Mn/p-Si device shows improved and enhanced optoelectronic performance in comparison to device fabricated using pure ZnS.

Highly responsive and low-cost ultraviolet sensor based on ZnS/p-Si heterojunction grown by chemical bath deposition

The chemical bath deposition method has been widely used to synthesize low-cost and large scalable UV light photodetectors. Herein, nanocrystalline ZnS thin films were deposited on p-Si substrates. The crystalline quality of the as-deposited ZnS thin films was studied using X-ray diffraction (XRD) and scanning transmission electron microscopy (STEM). It was found that ZnS films showed good crystallinity with the growth direction along the (111) planes of a cubic zinc blend structure, as confirmed by both XRD and STEM analysis. The crystallite size was calculated to be 2.49 nm which is very close to the Bohr radius. Optical measurements revealed a blue shift of 5 nm which indicates quantum confinement effects in the as-deposited ZnS films. Furthermore, the morphology and grain size of ZnS film was estimated from scanning electron microscopy (SEM). Photoluminescence (PL) measurements showed evidence of multiple emissions in the as-deposited ZnS films, indicating the presence of commonly known intrinsic defects, for instance, Zn and S vacancies. The fabricated heterojunction ZnS/p-Si yields a high sensitivity (1.98 ×104), fast response and high peak detectivity (4.29 × 1012). The device showed a good responsivity of (68.98 mA/W) without biasing towards the UV light (350 nm) regime. Moreover, the linear Dynamic Range of 85.92 dB and the External Quantum Efficiency (EQE) of 23.42 % was obtained that can be utilized for UV photodetectors applications.

Enhanced solar-cell efficiency via fabricated zinc sulfide nanocrystalline thin film-based Schottky diodes as a bypass: An experimental and theoretical investigations

This work represents experimental and theoretical investigations on the electrical characteristics of ZnS nanocrystalline thin films synthesized via sonicated (UCBD) and un-sonicated (CBD) chemical bath deposition technique and the fabrication of Schottky junction diodes, for potential solar cell incorporation and other opto-electronic applications. The sonication induced ZnS nanocrystalline thin films (SNP) at frequency 20 kHz–1 MHz and without sonication induced ZnS nanocrystalline thin films (NP) deposited on an indium tin oxide (ITO) substrate. A rapid thermally evaporated lightly doped Ag on SNP and NP-ZnS transparent thin films in the high range of vacuum (~10−6 Torr), has been achieved. The current density-voltage (J-V) and capacitance-voltage (C-V) measurements of fabricated Schottky diodes were carried out employing a potentiostat device. The enhanced performance of fabricated Schottky devices has been quantified by analyzing their J-V characteristics using established Landauer transport formalism. Ideal diode behavior has been confirmed by a low voltage drop of 0.35 V, and low junction capacitance ~3.21 nF across fabricated Schottky diodes. The maximum blockage of leakage current across fabricated Schottky diodes have been detected as compared to the available commercial diodes. The Landauer transport model found to be excellent fitting for understanding the electron transport mechanism for these fabricated diodes. The Fermi energy level pinned near effective gap center that shifts under the bias condition due to the metal induced gap states. The Schottky diodes as a bypass in solar cell panel demonstrates the significant enhancement in photo-response and efficiency of solar cell in the presence of sunlight.

Effect of cobalt doping on the structural, optical and magnetic properties of sol-gel derived ZnS nanocrystalline thin films and ab initio studies

The effect of Co doping on the structural, optical and magnetic properties of sol-gel derived ZnS films was investigated for their dilute magnetic semiconducting behaviour. X-ray diffraction pattern shows nanocrystalline nature of the films. Raman spectroscopy was used to study the vibrational properties of the films and also to identify any kind of secondary phases. The surface morphology and roughness of the films was analysed through scanning electron microscopy and atomic force microscopy. The chemical binding state of Co in ZnS lattice was confirmed from the X-ray photoelectron spectroscopy. The optical band gap is found to be decreasing with the incorporation of Co in ZnS. The red emission ~1.7 eV ensures tetrahedral occupation of Co atoms in ZnS lattice. The observed room temperature ferromagnetism in Co:ZnS films is attributed to carrier induced magnetization as well as to the intrinsic defects. The origin of magnetism in Co:ZnS system was studied in terms of the spin-polarized electronic density of states obtained through the density functional theory.

Application of Chlorophyll as Sensitizer for ZnS Photoanode in a Dye-Sensitized Solar Cell (DSSC)

Zinc sulphide thin films have been synthesized by the electrodeposition method onto stainless steel substrate followed by dipping in acetone solution of chlorophyll in different time intervals to form photosensitised thin films. The photoelectrochemical parameters of the films have been studied using the photoelectrochemical cell having the cell configuration as follows \( {\rm{photoelectrode/NaOH}}\left({1\;{\rm{M}}} \right) + {\rm{S}}\left({1\;{\rm{M}}} \right) + {\rm{N}}{{\rm{a}}_2}{\rm{S}}\left({1\;{\rm{M}}} \right){\rm{/C}}\,\,\left({{\rm{graphite}}} \right)\). The photoelectrochemical characterization of the semiconductor film and dye-sensitised films has been carried out by measuring current–voltage (I–V) in the dark, power output and photoresponse. The study proves that the conductivity of both ZnS film and dye-sensitised ZnS films are n-type. The power output curves illustrate that open circuit voltage (Voc) and short circuit current (Isc) increase from 0.210 V to 0.312 V and from 0.297 mA to 0.533 mA, respectively. The fill factor initially decreases from 0.299 to 0.213 and then increases to 0.297 irregularly whereas efficiency increases from 0.047% to 0.123%. The UV–Vis absorbance spectrum of chlorophyll in acetone shows the presence of chlorophyll. The structural morphology of the ZnS thin films has also been analysed by using x-ray diffraction technique (XRD) and a scanning electron microscope (SEM). The XRD pattern shows the formation of nanocrystalline ZnS thin films of size 65 nm and the SEM images confirm the formation of fibrous film of ZnS. The energy diffraction analysis of x-ray confirms the formation of ZnS thin films.

Influence of thiourea on the synthesis and characterization of chemically deposited nano structured zinc sulphide thin films

Nanocrystalline ZnS thin films incorporated onto glass substrates by chemical bath deposition method were investigated by X-Ray Diffraction (XRD), Atomic Force Microscopy (AFM), UV–Visible Spectroscopy (UV–Vis), Photoluminescence (PL), and Raman Spectroscopy (FT-R) studies. The influence of thiourea on the structural and optical properties of ZnS films was discussed in detail. The X-ray diffraction patterns confirmed the rhombohedral structure of ZnS thin films. AFM measurements indicated the nano carpet-like surface morphology variation in film with influence of thiourea. The optical absorption studies in the wavelength range of 200–800 nm showed that the band gap energy of ZnS has decreased from 3.69–3.36 eV, as thiourea varied from 0.2–0.8 M. The PL spectra divulged a shift near band edge emission around 360 nm, when thiourea concentration was increased. The Stokes shift calculations from PL emission spectra supported the relative intensities estimated from PL energy band spectra and showed a dependable repeatability for different molar concentrations. The Zn–S complexes were identified in the Raman spectra and the Raman spectral shift for 0.6 M composition of thiourea, which was found to be appreciable for ZnS thin films. The characterization studies clearly exposed the effect of thiourea onto the chemically deposited ZnS thin films.

Experimental and Simulation Study on Nanosonic Particles and Nanomaterials of ZnS and Their Nano-Schottky Diodes

Monte Carlo simulation is applied for the first time to understand the growth mechanism in ZnS nanosonic particles. Particles are considered as hard disks interacting through a square-well potential. The ZnS cluster growth observed in nanosonic and nanoparticles is captured by this model. The estimated binding energy in nanosonic particles is approximately 10 times lesser than in nanoparticles. Role of acoustic cavitations and magnetic agitations shows compact and uniform nanocrystalline ZnS thin films with a transparent window layer for photovoltaic and biosensor application. The approach of distortion from zinc blende to hexagonal closed packed is observed in X-ray diffraction. A small uniform granular morphology and grain size 50–100 nm are observed in scanning electron microscopy. The emission spectra excited at wavelength 270 nm show a strong emission peak in the range of 330–335 nm. Transmission electron microscopy showed a particle size of 53 and 100 nm for ultrasonic chemical bath deposition and c...

Intrinsic defects and structural phase of ZnS nanocrystalline thin films: effects of substrate temperature

Fabrications of ZnS nanocrystalline thin films at different substrate temperatures (TS) of 200, 300 and 400 °C by means of pulsed laser deposition are presented. Thin film deposited at TS of 200 °C is in cubic zinc-blende (ZB) structure while those deposited at TS of 300 and 400 °C are in hexagonal wurtzite (W) phase. The grain size, surface roughness and bandgap of the films increases with increasing TS. The zinc vacancies and interstitials in the films increases while sulfur vacancies decreases with increasing TS. The variation of zinc and sulfur vacancies in ZnS films with TS is responsible for structural phase transition from ZB to W which causes the change in energy bandgap.

Synthesis of europium-doped ZnS nano-crystalline thin films with strong blue photoluminescence

Eu2+-Doped ZnS (ZnS:Eu2+) thin (∼550 nm) films with strong and stable blue photoluminescence have been successfully synthesized by a simple and fast ultrasonic spray pyrolysis method.

Room temperature ferromagnetism and half metallicity in nickel doped ZnS: Experimental and DFT studies

The nickel doped nanocrystalline ZnS thin films were deposited onto glass substrates by chemical bath deposition (CBD). Also ZnS:Ni nanoparticles were synthesized by CBD/co-precipitation method. Powder X-ray diffraction (p-XRD) studies demonstrate that both thin films and nanoparticles correspond to sphalerite (cubic) phase of ZnS with slight shift towards higher 2θ values due to incorporation of nickel in the ZnS lattice. The crystallite sizes estimated by Scherrer equation were 4 and 2.6 nm for ZnNiS thin films and nanoparticles, respectively. Scanning Electron Microscopy (SEM) images reveal that the morphology of thin films is based on quasi-spherical particles with nano scale dimensions. Energy Dispersive X-ray (EDX) spectroscopy confirms that the as-deposited thin films have a stoichiometry consistent with the nickel doped ZnS. Full-potential linearized augmented plane wave (FP-L/APW) method based on spin-polarized density functional theory (DFT) was employed to investigate the electronic and magnetic properties of ZnNiS for the doping concentration. Exchange-correlation functional was studied using generalized gradient approximation (GGA + U) method. Electronic band structures and density of states (DOS) demonstrate 100% spin polarization (half metallicity) with ferromagnetic exchange interactions. Superconducting quantum interference device (SQUID) analysis confirms the theoretical observation of ferromagnetism in nickel doped ZnS. These ZnS based half metallic ferromagnets seem to have virtuous applications in future spintronic devices.

Photoluminescence of nanocrystalline ZnS thin film grown by sol-gel method.

Nano and polycrystalline ZnS thin films play a crucial role in photovoltaic technology and optoelectronic devices. In this work, we report the photoluminescence (PL) characterization of nanocrystalline ZnS thin films synthesized by dip coating method. The PL spectra exhibit broad nature with multiple emission peaks which are due to the different defect levels in the prepared film.

Effect the Temperature on Structure and Optical Properties for ZnS nanostructure Thin Film

ZnS nanocrystalline thin films by different temperature of reaction were prepared by chemical bath deposition using thiourea and zinc acetate as S2– and Zn2+ source. The optical absorption studies in the wavelength range 200–1100 nm show that band gap energy of samples 3.75 and 4.0 eV for different temperature reaction condition. The refractive index was estimated within the visible wavelength at 623 nm, it was 2.04 for sample 1 and its value will increase for sample 2 to be 2.55. The room temperature photoluminescence spectra of the films showed two peaks for all samples. We assigned the first peak due to band gap transitions while the latter was due to zinc vacancy in the films. Structural analysis using atomic force microscopy shows that the grain size for films were 73.2 and 87.34 nm. X-ray diffraction analysis indicates that both of them formed in the reaction bath have cubic zinc blende structure .The structural estimation shows variation in grain size 7nm and 20nm with different temperature reaction.

Optimising conditions for the growth of nanocrystalline ZnS thin films from acidic chemical baths

The growth of nanocrystalline zinc sulfide thin films onto glass substrates by chemical bath deposition has been optimized at acidic pH. Powder X-ray diffraction (p-XRD) confirms the deposition of sphalerite, the cubic phase of ZnS. The crystallite size calculated by Scherrer equation was found to be 4.0nm. Scanning Electron Microscopy (SEM) show clusters of spherical nanoparticles uniformly distributed over the surface of the glass substrates. Energy Dispersive X-ray (EDX) analysis of the deposited thin films show the zinc to sulfur ratio close to 1:1. The observed band gap (3.78eV) of the deposited thin films is higher than that reported for cubic phase of bulk ZnS (3.54eV) as expected due to nano-size crystallites. Binding energies calculated by X-ray Photoelectron Spectroscopy (XPS) confirm the material as ZnS and the photoluminescence measurements show the blue shift in emission maximum.

Fabrication and characterization of nano-structured ZnS thin films as the buffer layers in solar cells

High quality nanocrystalline ZnS thin films were deposited on glass substrates by a chemical bath deposition (CBD) method from an aqueous solution containing triethylamine, as a nontoxic complexing agent for zinc ions, at temperatures ranging from 50 to 90 °C. The effects of the deposition time and temperature on thickness as well as structural, morphological and optical properties of the ZnS thin films were examined by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and ultraviolet-visible (UV-vis) spectroscopy. Fourier transform infrared spectroscopy (FT-IR) studies were done to investigate the presence of organic and/or other compounds in films. UV-vis spectroscopy data revealed the obtained ZnS films to have an optical band gap ranging from 4.1 to 3.9 eV. XRD results showed that the prepared films were highly crystalline with a cubic zinc blende structure consisting of very small nanocrystallites, 2.0–2.5 nm in size, showing quantum confinement effects.

Effect of four different zinc salts and annealing treatment on growth, structural, mechanical and optical properties of nanocrystalline ZnS thin films by chemical bath deposition

ZnS thin films were deposited from four different zinc salts on glass substrates by chemical bath deposition method. Different anions of zinc salts affect the deposition mechanism and growth rate, which influence the properties of the films significantly. The ZnS thin film deposited from ZnSO4 is smoother, thicker, more homogeneous and compact, nearly stoichiometric, comparing with the films deposited from Zn(CH3COO)2 and Zn(NO3)2, and ZnCl2. The scratch test of bonding force between ZnS film and substrate shows that the ZnS film deposited from ZnSO4 has the most excellent adhesion with the substrate. The presence of SO42− promotes heterogeneous ZnS thin film growth via ions by ions deposition, and the films deposited from Zn(CH3COO)2 and Zn(NO3)2 are formed via clusters by clusters deposition. XRD and HRTEM results show that cubic ZnS films are obtained after single deposition, and the grain size of ZnS thin film deposited from ZnSO4 for 2.5h is 10nm. The average transmission of all films is greater than 85% in the wavelength ranging from 600 to 1100nm, and the transmission of films deposited from ZnSO4 or Zn(NO3)2 for 1.5, 2 and 2.5h is greater than 85% in the wavelength varying from 340 to 600nm, which can enhance the blue response. The band gaps of all ZnS thin films are in the range of 3.88–3.99eV. After annealing treatment, the mechanical and optical properties of the ZnS thin film deposited from ZnSO4 are improved significantly.

Preparation and characterization of ZnS nanocrystalline thin films by low cost dip technique

Nanocrystalline ZnS semiconducting nanopowder and thin films have been deposited by simple low cost technique based on combination of dip coating and thermal reaction process. The deposited films and the prepared nanopowder have been characterized in the structurally, optically and electrically point of views. The effect of preparation conditions has been also optimized for good quality films. X-ray diffraction analysis performed the ZnS cubic phase in the reaction temperatures in the range 473–593 K. Above 593 K mixed cubic and hexagonal crystallographic phases have been resolved. Crystallite size and micro strain have been calculated to be 2.65 and 0.011 nm, respectively. The deposited film surface and cross section morphologies show that neither cracks nor peels have been observed and good film adhesion with the substrate was performed. Energy dispersive X-ray measurements of the film agree well with the calculated concentrations of the precursor components. Optical measurements confirm the optical characteristics of nanocrystalline ZnS film such as absorption and dispersion properties. Copper doped ZnS reduces the band gap while indium doped ZnS increases the band gap. Electrical characterization shows that copper doped ZnS increases the resistivity by one order of magnitude due to electron compensation process while indium doped ZnS decreases the resistivity three orders of magnitude due to increase of the carriers concentration. Hot probe thermoelectric quick test of ZnS:Cu and ZnS:In show opposite sign of thermoelectric voltage due to bipolar p and n types, respectively.

Zinc vacancy mediated structural phase transition and photoluminescence in nanocrystalline ZnS thin films

Nanocrystalline thin films of zinc sulphide were prepared on glass substrate at various deposition temperatures by thermal evaporation technique. The variation of the structural and optical properties of films deposited at various substrate temperatures was investigated in detailed. X-ray diffraction spectra showed that films deposited at 300 and 400 °C are polycrystalline in nature having cubic and both cubic and wurtzite structure, respectively. However, film deposited at temperature of 200 °C was found to be amorphous in nature. The ultra-violet and visible absorption studies showed that the band gap of films increases with increase in deposition temperatures. Photoluminescence spectra displayed emission near 396 and 444 nm, which arises due to zinc vacancies and sulphur vacancies, respectively and has been correlated to phase transition of the films.

Room temperature ferromagnetism in Mn-doped ZnS nanocrystalline thin films grown by sol–gel dip coating process

Nanocrystalline Zn1−xMnxS (x = 0.00, 0.01, 0.02, 0.03, 0.05, and 0.1) thin films having different Mn content were grown by the sol–gel dip coating process. The effect of Mn content on the structural, optical and magnetic properties of Zn1−xMnxS nanocrystalline thin films were investigated. X-ray diffraction results showed the presence of single hexagonal phase corresponding to ZnS with a preferred orientation along the ZnS (002) hexagonal plane direction without any detectable secondary phase, suggesting the incorporation of Mn ions into the ZnS lattice. Scanning electron microscope revealed the surface of the nanocrystalline films to be homogeneous and dense and the grains of the film surface were randomly scattered. In ultraviolet–visible measurements, the band gap energy corresponding to the absorption edge estimated were found to be 3.59–3.23 eV depending on the Mn doping ratio. Magnetic measurements showed that a paramagnetic behavior at 5 K and ferromagnetic behavior at 300 K.

Absence of room temperature ferromagnetism in Mn-doped ZnS nanocrystalline thin film

Mn-doped ZnS nanocrystalline thin films having composition Zn1−xMnxS (x=0.02, 0.05, 0.1 and 0.15) were prepared by the electron beam evaporation technique. Their structural and magnetic properties had been investigated. X-ray diffraction results show single phase of hexagonal type structure samples without any detectable secondary phase providing the evidence that Mn2+ ions are incorporated into the ZnS lattice. Evidence of nanocrystalline nature of the films was observed from the investigation of surface morphology using atomic force microscopy. The magnetic measurements at 5K reveal superparamagnetic behavior. The field dependent magnetization measurements confirm the absence of the room temperature ferromagnetism in the single phase electron beam evaporated Zn1−xMnxS (x=0.02, 0.05, 0.1 and 0.15) nanocrystalline films. Furthermore, the inverse susceptibility versus T confirms paramagnetic behavior for the Mn-doped films in the temperature range 100K≤T≤300K. The absence of significant impurities and/or defects could be attributed to explanation for the absence of free carriers and consequently the absence of room temperature ferromagnetism in all nanocrystalline Zn1−xMnxS films. The absence of room temperature ferromagnetism is evidence by marked concave nature of Arrott's plot without any spontaneous magnetization.

Highly Luminescent and Temperature Stable Quantum Dot Thin Films Based on a ZnS Composite

A solution processable Zn(EtXn)2(octylamine) precursor has been used to deposit nanocrystalline ZnS thin films which can effectively host CdSe–CdS–ZnS quantum dots (QDs) with their native surface chemistry intact. The formation of such hybrid QD:ZnS composites proceeds through the initial decomposition of the octylamine stabilized zinc xanthate precursor to form nanocrystalline ZnS. To gain insight into this decomposition process we have utilized headspace gas chromatography–mass spectrometry (HS GC-MS), thermogravimetric analysis coupled with mass spectrometry (TGA-MS), grazing angle attenuated total reflectance Fourier transform infrared spectroscopy (GAATR FTIR), and grazing angle X-ray diffraction (GAXRD). Through these characterizations we identify that the major decomposition route of Zn(EtXn)2(octylamine) to form ZnS begins at 100 °C, generating predominantly CO2, COS, CS2, and ethanol as gaseous products. The octylamine used to solubilize the metal complex is found to remain adsorbed within the Zn...