Doped ZnSe Thin Films Research Articles

Effects of terbium ions on the structural, morphological and optical properties of zinc selenide thin films prepared by photo-assisted chemical bath method

This study presents undoped and terbium doped ZnSe thin films deposited at different terbium III (Tb3+) ion concentrations using Photo-assisted chemical bath technique. The samples were characterized using glancing incidence X-ray diffraction (GIXRD), Raman spectroscopy, ultraviolet-visible spectroscopy, and photoluminescence (PL) spectroscopy, field emission scanning electron microscope, Atomic force microscopy and energy dispersive X-ray spectroscopy. The GIXRD and Raman peaks intensities, surface roughness and energy band gap increased with increasing Tb3+ ions concentration up to 0.8% and decreased thereafter. This behavior, which is equally observed in the PL emission, is ascribed to concentration quenching due to the presence of natural defect in the host material. Three PL emission peaks all associated with the defects were observed at 535, 672 and 743 nm. The thin films morphology transformed from flakes to spherical grains with increased Tb3+ ions concentration and the presence of the expected elements was confirmed. The deposited films have potential applications in light emitting devices.

Tailoring Structural and Optical Properties of Cu Doped Chemically Deposited ZnSe Nanostructured Thin Films

Chemical bath deposition has been used for depositing undoped and copper doped ZnSe thin films at 343 K temperature. Growth of the thin film requires zinc sulphate cation and sodium selenosulphate anion. The preparative parameters are optimized with an aim to obtain high quality thin films. Three different concentrations of Cu source are used. XRD pattern indicates the incorporation of copper in to polycrystalline cubic ZnSe in doped thin films and is confirmed by EDAX spectrum. SEM micrographs indicate that ZnSe dispersion in the films is homogeneous. UV–visible transmission spectra of the thin films have put into evidence that the dispersion of ZnSe nanocrystals in the thin film is improved their optical transmission. Room temperature PL spectra have shown that the addition of Cu into ZnSe enhanced the emission with additional green peak other than blue band edge emission. Electrical conductivity also modified on addition of Copper.

Influence of Precursor Temperature on Bi Doped ZnSe Material via Electrochemical Deposition Technique for Photovoltaic Application

In this study, Bismuth (Bi) doped ZnSe thin films were deposited on conducting glass substrates by electrochemical deposition technique and the influence of precursor temperature (room, 50, 55, 60 oC) on their optical and structural properties were systematically studied using the combined effect of X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM) and UV-VIS spectrophotometer. The XRD patterns show a face-centred cubic structure indexed with peaks at (220), (221) and (300). The grain size was in the range of 3.24056 to 4.60481 nm with a lattice constant of 7.189Å. The material deposited at room, 500C, 550C, and 600C reveals agglomeration of particle on the surface of the substrate indicating uniform deposition. The optical spectra show that at different temperature (say room, 50oC, 55oC and 60oC), the absorbance and reflectance of BiZnSe thin films decreases with increase in wavelength of the incident radiation while the transmittance shows direct proportionality with the increase in wavelength. The bandgap demonstrated an increase in the range 1.75-2.25 eV with increase in temperature.

The effects of doping and temperature on properties of electrochemically deposited Er3+ doped ZnSe thin films

Zinc Selenide (ZnSe) is a binary chalcogenide with band gap (Eg) of about 2.70 eV. Doping is used to tune band gap in order to optimize electrical and optical properties of thin films. The aim of this work was to determine the effects of doping and deposition temperature on the properties of erbium doped zinc selenide (Er3+;ZnSe). Undoped ZnSe and Er3+;ZnSe (1–4%)] were deposited at room temperature and at deposition temperatures between 40 °C and 100 °C on fluorine doped tin oxide (FTO) glass by electrochemical technique. The effects of doping and deposition temperature on the crystal structure, morphology, optical and electrical properties of the deposited ZnSe were investigated. XRD results showed that both undoped and Er3+;ZnSe were crystalline in nature with strong orientation along (111) and (311) directions. Peak intensity of Er3+;ZnSe decreased from Er1% to Er3% as doping concentration increased and then increased as concentration increased to 4%. The peaks were indexed to the cubic structure of ZnSe thin film with Er2% showing the highest purity. The UV–vis result revealed that the samples deposited at higher deposition temperatures [Er4%(80 °C) and Er4%(100 °C)] showed lower transmittance. Undoped ZnSe had band gap of 2.75 eV which approximated the bulk value. The band gap was observed to decrease as deposition temperature increased. The films deposited at room temperature had wider band gap (2.9 eV–2.61 eV) than those deposited above room temperature (2.21 eV–1.69 eV). The SEM micrograph revealed that low doping concentration (Er1%) had no effect on morphology. Er2% had the highest resistivity of about 8.41 × 103 Ωcm and lowest conductivity of 1.19 × 10−4 Ωcm−1. Doping and deposition temperature thus affected most of the investigated properties. Er3+;ZnSe (Er1% - Er4%) and Er4% (40 °C) – Er4% (100 °C) find applications as solar cell buffer layers and absorbers respectively.

Structure and optical properties of thermally evaporated Te doped ZnSe thin films

The cooled pressing method is used for preparing (ZnSe)1−xTex chalcogenide glasses. The thermal evaporation technique is utilized for depositing the thin films. Topological calculations reveal the obvious effect of doping Te content on the average coordination number Z, parameter determines the deviation from stoichiometry r, glass transition temperature Tg, number of lone-pair electrons L and heat of atomization Hs. Swanepoel's approach is used to estimate the refractive index and the average thickness of the films with high accuracy. The addition of tellurium as an impurity found to has a great influence on the optical parameters such as refractive index, energy band gap Eg, Urbach energy Eu, refractive index n, single oscillator energy Eo, dispersion energy Ed, free-electron concentration N, and plasma frequency, ωp.

Comparative study of structural, optical and electrical properties of electrochemically deposited Eu, Sm and Gd doped ZnSe thin films

A facile approach involving electrochemical deposition method was utilized to coat ITO substrate with zinc selenide thin films at different rare earth metal (Eu3+, Sm3+ and Gd3+) ions. The characteristics of deposited films were studied in relation with the doped metal ions. The structure of the coating was confirmed to be hexagonal wurtzite in (101) plane by X-ray analysis. The new antistructural modeling shows that the doping of ZnSe lattice by rare earth cations increases the concentration of the surface active centers such as $${\text{Gd}}_{{{\text{Zn}}}}^{\cdot },\,{\text{Eu}}_{{{\text{Zn}}}}^{\cdot },\,{\text{Sm}}_{{{\text{Zn}}}}^{\cdot },\,{\text{and}}\,{\text{V}^{\prime\prime}_{{\text{Zn}}}}$$, which are located in the cationic sublattice. XRD data revealed that the average crystallite size of ZnSe and ZnSe:Eu, ZnSe:Sm, and ZnSe:Gd was 63, 54, 47, and 49 nm, respectively. The morphological results by scanning electron microscopy indicate that the spherical-like structure with agglomeration of grains and a slight increase in the particle size. Energy dispersive X-ray, UV–Visible and photoluminescence spectroscopy were used to study the composition and optical properties of the films. A blue-shift was observed in ZnSe thin films. The bandgap energy of undoped ZnSe and ZnSe:Eu, ZnSe:Sm, and ZnSe:Gd were found to be 2.28, 2.44, 2.68 and 2.75 eV, respectively. Among the different coated films, the Gd3+ ion doped ZnSe thin film exhibited a lesser charge transfer resistance of 25.5 Ω as analyzed from the electrochemical impedance measurement. The photoelectrochemical studies reveal that the rate of photoinduced charge carriers was higher in Gd3+ ion doped thin film. The present studies suggested that the Gd3+ ion doped ZnSe thin film can be a promising material for electrochemical device applications.

Physicochemical and electrochemical properties of Gd3+-doped ZnSe thin films fabricated by single-step electrochemical deposition process

Gd3+ (gadolinium)-doped ZnSe thin films (1 to 5 mol%) are grown onto indium-doped tin oxide (ITO) glass substrate by single-step electrochemical deposition process. X-ray diffraction analysis confirms the formation of hexagonal wurtzite structure with preferred growth orientation along (101) plane. A new antistructural modeling for describing active surface centers for ZnSe:Gd system is discussed for the first time. The new antistructural modeling shows that the dissolution of Gd cations increases the concentration of surface active centers $$ {\mathrm{Gd}}_{\mathrm{Zn}}^{\bullet } $$ and $$ {\mathrm{V}}_{\mathrm{Zn}}^{\prime \prime } $$ , which are located in the cationic sublattice. The surface morphology of thin films investigated using scanning electron microscopy reveals some agglomeration of grains with significant changes in particle size with varying Gd3+ concentrations. UV-vis and photoluminescence studies indicate a blue shift due to the incorporation of Gd3+ into ZnSe host lattice. Electrochemical impedance spectroscopy and photoelectrochemical measurements reveal that the 3 mol% Gd3+-doped ZnSe thin film possesses low charge transfer resistance (25.42 Ω) and faster migration of photoinduced electrons, resulting in high conductivity. Therefore, the optimum doping concentration, 3 mol% Gd3+-doped ZnSe, offers a positive synergistic effect for photoelectrochemical devices.

Electrochemically synthesized 1D and 3D hybrid Fe3+ doped ZnSe dandelions for photoelectrochemical cell application

In the present study, Fe3+ doped ZnSe thin films are deposited using the galvanostatic mode of electrodeposition. Further, deposited thin films are characterized using X-ray diffraction study, X-ray photoelectron spectroscopy and Raman spectroscopy for their confirmation. After that morphological study is carried using field emission scanning electron microscopy, topological study is carried using atomic force microscopy (AFM). Optical properties are studied using optical absorbance and photoluminescence. The electrochemical properties are studied using electrochemical impedance spectroscopy. The most important part is study of photoelectrochemical properties. In the present study, 0.75% Fe3+ doped ZnSe thin film shows the relatively better photoelectrochemical cell performance than the other deposited thin films due to dandelion like nature. The observed short circuit current is 155μA and open circuit voltage is 487mV. The calculated Fill factor and efficiency are 0.35 and 0.17%, respectively.

Optical, magnetic, and photoelectrochemical properties of electrochemically deposited Eu3+-doped ZnSe thin films

The various mole percent (1–5%) of Eu3+-doped ZnSe thin films were fabricated on the indium-doped tin oxide (ITO) conducting glass substrate by single-step electrochemical deposition (ECD) process in an aqueous medium at 50 °C. The structural, optical, magnetic, and electrochemical properties were characterized as a function of the Eu3+ ion concentration. The X-ray diffraction (XRD) analyses evidenced that the films were hexagonal wurtzite structure along with the (101) preferential orientation. High-resolution scanning electron microscopy (HRSEM) results revealed that the thin films show a spherical like structure for 1–3% of Eu3+-doped ZnSe films. Further, increasing of Eu3+ concentration (4 and 5%), the surface morphology of thin films was observed as agglomerated grain-like structure. The band gap energy of Eu3+-doped ZnSe thin films (2.35 to 2.49 eV) determined by UV-Vis spectra showed a blue shift of absorption edge compared to the pure ZnSe thin film (2.33 eV). The increased band gap by doping of Eu3+ is due to the quantum size effect. The PL emission intensity enhanced by increasing Eu3+ concentration which revealed the enhanced radiative recombination in the luminescence process. The magnetic study revealed that Eu3+-doped ZnSe thin films were ferromagnetic in nature. Electrochemical impedance analysis indicated that 4% of Eu3+-doped ZnSe thin films showed a lower charge transfer resistance (352 Ω) and excellent properties compared to the other samples. Further, the photoelectrochemical measurements carried out for the optimized 4% Eu3+-doped ZnSe thin film revealed the faster migration of photoinduced charge carriers. The present investigation demonstrates that the electrochemically deposited Eu3+-doped ZnSe thin film is a promising candidate for electrochemical device applications.

Studies of properties of Fe3+ doped ZnSe nanoparticles and hollow spheres for photoelectrochemical cell application

Present work reports a photoelectrochemical cell performance of Fe3+ doped ZnSe nanoparticles and hollow spheres. These nanoparticles and hollow spheres are deposited using simple potentiostatic mode of electrodeposition with varying of Fe3+ doping percentage. The auxiliary conformations of phase formation through experimental investigation such as XRD, XPS and FT-RAMAN have been done and the results are found consistent with each other. The AFM studies aggress well with FESEM results which eventually confirm formation of nanoparticles. The 0.75% Fe3+ doped ZnSe shows the better photoelectrochemical cell performance due to nanoparticles, relatively less charge transfer resistance, relatively better absorbance, less band gap etc. The observed short circuit current is 175 μA and open circuit voltage is 575 mV. The calculated fill factor and efficiency are 0.32 and 21%, respectively for 0.75% Fe3+ doped ZnSe. The relatively lower value of series resistance of 0.75% Fe3+ doped ZnSe thin film as compared to other deposited films is also responsible for better efficiency of photoelectrochemical cell.

Effect of Sm3+ on the structural, optical, magnetic and electrical properties of electrochemical deposition of ZnSe thin films

Zn1−xSmxSe thin films with an Sm3+ concentration of x = 1 to 5 mole % were grown on ITO substrates at 50 °C using the electrochemical deposition (ECD) technique. The structural, optical, magnetic and electrical properties were analyzed as a function of the Sm3+ ion concentration. The glancing angle x-ray diffraction (GAXRD) characterisation of doped systems at various Sm3+ mole fractions x confirmed the exclusive formation of the host ZnSe with the zinc blende structure. The optical transmission spectra show that the percentages of transmission and band gap energy are different for pure and Sm3+ doped ZnSe thin films. Photoluminescence (PL) spectra of 1 to 5 mole % Sm3+ ion doped ZnSe thin films show two distinct ZnSe and Sm3+ related emissions, both of which are excited via the ZnSe host lattice. A sharp luminescence peak from Sm3+ doped ZnSe at 1.83 eV, which can be assigned as the 4G5/2 → 6H9/2 transition of Sm3+, was observed. The magnetization of Sm3+ doped ZnSe thin films was measured as a function of the magnetic field and temperature. The magnetic behaviour of magnetic semiconductor Sm3+ doped ZnSe, with no secondary phase, is reported. Electrical measurement showed that when the Sm3+ ion is incorporated, the electrical resistivity drops and the carrier concentration increases.

Studies of properties of Fe2+ doped ZnSe nano-needles for photoelectrochemical cell application

Present work reports a photoelectrochemical cell performance of Fe2+ doped ZnSe nano-needles. These nano-needles are deposited using simple galvanostatic mode of electrodeposition with varying of Fe2+ doping percentage. The auxiliary conformations of phase formation through experimental investigation such as XRD, XPS and FT-RAMAN have been done and the results are found consistent with each other. The AFM studies aggress well with FESEM results which eventually confirm formation of nano-needles. The 1 % Fe2+ doped ZnSe shows the better photoelectrochemical cell performance due to nano-needles, relatively less charge transfer resistance, relatively better absorbance, less band gap etc. The observed short circuit current is 220 µA and open circuit voltage is 504 mV. The calculated fill factor and efficiency are 0.32 and 0.23 %, respectively for 1 % Fe2+ doped ZnSe. The relatively lower value of series resistance of 1 % Fe2+ doped ZnSe thin film as compared to other deposited films is also responsible for better efficiency of photoelectrochemical cell.

Solution-based Ag-doped ZnSe thin films with tunable electrical and optical properties

Thin film transistors fabricated using ZnSe thin films synthesized using chemical bath deposition.

Pulsed laser deposition of chromium-doped zinc selenide thin films for mid-infrared applications

We have grown Cr doped ZnSe thin films by pulsed laser deposition on GaAs, sapphire and Si substrates through KrF excimer laser ablation of hot-pressed targets containing appropriate stoichiometric mixtures of Zn, Se, and Cr species and hot-pressed ceramic targets made of ZnSe and CrSe powders in vacuum and in an He background environment (10-4 Torr). Deposited films were analyzed using X-ray diffraction to determine crystallinity and energy dispersive X-ray fluorescence to confirm Cr incorporation into the films. Photoluminescence measurements on the films show intracenter Cr2+ emission in the technologically important 2–2.6 μm spectral range.

Study of the recombination around the excitonic region of MBE ZnSe:Cl thin films

The recombination processes around the excitonic region of undoped ZnSe and chlorine doped ZnSe thin films were studied by continuous-wave photoluminescence (cw-PL) and time-resolved photoluminescence (TRPL) spectroscopies. Samples with different chlorine concentration were obtained by varying the temperature of the Cl source. The evolution of the PL signal and its decay time were analyzed as a function of temperature. Activation energy (Ea) values associated to the quenching of the D0X and band-to-band emission were obtained from the temperature dependent cw-PL experiments. The activation energy was lower for the film with higher Cl content. The characteristic exponential decay time (τPL) of the PL signal decreased with increasing Cl concentration.

Structural, optical properties and VCNR mechanisms in vacuum evaporated iodine doped ZnSe thin films

Iodine doped ZnSe thin films were prepared onto uncoated and aluminium (Al) coated glass substrates using vacuum evaporation technique under a vacuum of 3 × 10 −5 Torr. The composition, structural, optical and electrical properties of the deposited films were analyzed using Rutherford backscattering spectrometry (RBS), X-ray diffraction (XRD), spectroscopic ellipsometry (SE) and study of I– V characteristics, respectively. In the RBS analysis, the composition of the deposited film is calculated as ZnSeI 0.003. The X-ray diffractograms reveals the cubic structure of the film oriented along (1 1 1) direction. The structural parameters such as crystallite size, strain and dislocation density values are calculated as 32.98 nm, 1.193 × 10 −3 lin −2 m −4 and 9.55 × 10 14 lin/m 2, respectively. Spectroscopic ellipsometric (SE) measurements were also presented for the prepared iodine doped ZnSe thin films. The optical band gap value of the deposited films was calculated as 2.681 eV by using the optical transmittance measurements and the results are discussed. In the electrical studies, the deposited films exhibit the VCNR conduction mechanism. The iodine doped ZnSe films show the non-linear I– V characteristics and switching phenomena.

Spectroscopic studies of molecular-beam epitaxially grown Cr2+-doped ZnSe thin films

Cr:ZnSe thin films were grown by molecular-beam epitaxy with the long-term goal of demonstrating a route for the development of transitional-metal-doped semiconductor lasers. Photoluminescence (PL) and PL lifetime measurements of doped thin films and bulk crystals indicate that Cr is incorporated in the optically active Cr2+ state up to levels of 5×1019cm−3. The shape of PL spectra and lifetime measurements of doped thin films compares favorably with that reported for bulk samples. A microcavity formed by film interfaces is responsible for differences in spontaneous emission observed between films and bulk crystals.

Properties of highly conducting nitrogen-plasma-doped ZnSe:N thin films

Values for the acceptor ionization energy, Ea, and compensating donor ionization energy, Ed, have been obtained from an analysis of variable-temperature photoluminescence data taken for a series of highly conducting nitrogen-plasma doped ZnSe thin films. Eawas found to be highly temperature dependent, with values ranging from Ea ~110 meV at low temperatures to ~60 meV at room temperature. The compensating donor ionization energy ranged from Ed ~31 meV at low temperatures to ~24 meVat room temperature. These results provide clear evidence of thenonhydrogenic nature of the nitrogen acceptor state in heavily doped ZnSe:N thin films and suggest that interstitial bonding of N, at two or more stable sites, may play a central role in the p-type doping and compensation of this material at high doping levels.