Nanocrystalline ZnSe Thin Films Research Articles

Wavelength dependence of nonlinear optical susceptibility of ZnSe nanocrystalline film

The present work reports the nonlinear optical susceptibility of nanocrystalline ZnSe thin films with different thicknesses, measured using third-order harmonic technology at irradiation wavelengths λ of 1200–1900 nm. The results show that the third-order nonlinear susceptibility χ(3) of ZnSe thin films is a function of the pump wavelength and film thickness. The χ(3) values for the thinner 202-nm film generally decreased with the redshift of the wavelength and were approximately 10−20 m2/V2 at λ ≤ 1500 nm and 10−21 m2/V2 at λ > 1500 nm. The χ(3) values for the thicker 1021-nm film did not follow a decreasing trend, but instead exhibited local peaks at 1350, 1500 and 1750 nm, with a maximum value of approximately 2.4 × 10−19 m2/V2 at λ = 1750 nm. Within 1200–1900 nm, the χ(3) of the thicker film was always greater than that of the thinner film. In addition, a weak second-order harmonic at wavelengths within 1100–1300 nm was observed for the 1021 nm ZnSe thin film. The large difference in the nonlinear optical properties between the thinner and thicker film samples is conjectured to be caused by the increased density of geometric defects and the gradual formation of local anisotropy with increasing film thickness. Nonlinear optical coefficient measurements of ZnSe thin films with different thicknesses over a broad spectrum are important for the application of these films in nonlinear thin-film optoelectronic devices.

Properties of ZnSe nanocrystalline thin films prepared by thermal evaporation

ZnSe thin films with thickness of 30 nm and 50 nm were prepared on Corning 7059 glass substrates at room temperature by applying periodically interrupted physical vapour deposition of ZnSe and various deposition rates. All as-deposited films were annealed at 200°C and some of them were further annealed at 400°C. Results from spectroscopic ellipsometry have shown that the porosity of the films which is important for the ethanol sensitivity decreases with increasing deposition rate and annealing temperature. The porosity changes caused by annealing of the films at 400°C are accompanied with thickness decrease.

Temperature effect on properties of chemical induced nanocrystalline ZnSe thin films

Chemical bath deposition method has been successfully employed for depositing ZnSe thin films at different temperature ranges from 298 to 353 K. The technique used to investigate structural, optical and electrical properties of these films have been X-ray diffraction (XRD), optical absorption and conductivity measurements. The X-ray diffraction study reveals the cubic structure of the ZnSe films oriented along the (111) direction at all temperatures ranges from 298 to 353 K. The structural parameters such as particle size, strain, dislocation density and number of crystallites are evaluated. Optical measurements has been done using UV spectra and optical energy gap was evaluated in the range of 2.82–3.04 eV at different temperature. The dark conductivity (σd) and photoconductivity (σph) measurements at different temperature range indicates that the conduction in these materials is through an activated process having single activation energies and both σd and σph values varies with the temperature. The values of carrier life time and trap depth have also been calculated.

Structural, optical and photo-electrical properties of nanocrystalline ZnSe thin films

Present paper reports the effect of deposition temperature on structure and electrical conduction mechanism of ZnSe thin films. Films have been fabricated on glass substrates using condensation technique. The depositions have been performed in presence of Ar at various substrate temperatures (298–373 K). X-ray diffraction (XRD) studies reveal hexagonal structure with texture changing from (002) to (102) on increasing substrate temperature. The crystallite size (6.1–8.4 nm), strain (− 0.0133 to − 0.00748 lin−2 m−4), dislocation densities (1.857 × 1016–1.015 × 1016 lin m−2) and stacking fault probability (0.0038–0.0041) have been calculated from XRD data. The optical gap (2.75–3.00 eV), refractive index (2.38–2.48) and ionicity (0.425–0.446) have been calculated using transmission measurements. The dark-conduction and photo-conduction behaviours have been studied in temperature range 253–358 K. The two activation energies of dark conduction have been explained using different models. The conduction mechanism has been identified based on Seto’s model of thermionic emission. The barrier height (0.17–0.28 eV), impurity concentration (1.26 × 1020–3.18 × 1020 cm−3) and surface states density (1.05 × 1014–2.15 × 1014 cm−2) have also been calculated.

X-ray studies: CO2 pulsed laser annealing effects on the crystallographic properties, microstructures and crystal defects of vacuum-deposited nanocrystalline ZnSe thin films

The influence of CO2 pulsed laser annealing on microstructural properties and crystal defects of nanocrystalline ZnSe thin films have been studied. X-ray diffraction was utilized to study these issues. Laser annealing led to enhance the film quality and decrease the crystal defects.

Influence of various complexing agents on structural, morphological, optical and electrical properties of electrochemically deposited ZnSe thin films

Electrochemical deposition (ECD) of ZnSe thin films from aqueous solution containing ZnSO4·7H2O, SeO2 and different complexing agents at bath maintained at 50 °C were investigated. The voltammetric curves were recorded in order to characterize the electrochemical behavior of Zn2+/SeO2 system with different complexing agent and to apply the appropriate range of potential for ECD. GAXRD studies confirms that as-deposited ZnSe thin films using with different complexing agents belongs to the hexagonal phase with (101) plane as the dominant peak. When EDTA, hydrazine hydrate and triethanolamine as complexing agents used, as-deposited films were shows that peaks due to the hexagonal phase along with hexagonal Se reflection observed. EDAX, AES, FESEM and UV–Visible spectrum were used to examine the compositions, morphologies and band gap of ZnSe thin films deposited on ITO glass substrate. A broad photoluminescence (PL) emission peak has been confirmed by a systematic blue-shift in emission peak due to the formation of nanocrystalline ZnSe thin films. In the Raman spectra, high intensity peak of LO phonon mode is observed at 251 cm−1 using ammonia, citric acid, ethylenediamine and polyvinyl alcohol as a complexing agents. For EDTA, hydrazine hydrate and triethanolamine as a complexing agents used, the phonon was shifted toward lower frequencies. The conductivity type, resistivity, carrier concentrations and electron mobility were measured for the as-deposited ZnSe thin films. As-deposited ZnSe thin films using all complexing agents have n-type conductivity. Electrochemical impedance spectroscopy (EIS) indicated that the ethylenediamine as a good complexing agent for ZnSe thin film deposition and the films demonstrate a less charge transfer resistance (Rct is 11 Ω) with excellent conductivity compared to other samples.

Preparation and characterization of chemical bath deposited nanocrystalline ZnSe thin films using Na3-citrate and hydrazine hydrate: A comparative study

In this paper, a comparative study reported on the characteristics of Zinc Selenide (ZnSe) thin films prepared by a chemical bath deposition method using the non-toxic tri-sodium citrate (Na3-citrate) and toxic hydrazine hydrate (HH) as complexing agents. Morphological, structural, chemical, and optical properties were investigated using field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV–vis spectroscopy. FE-SEM and AFM studies revealed that the ZnSe thin film prepared using Na3-citrate was highly uniform with very low surface roughness (3nm) compared to those prepared using HH. XRD and XPS studies revealed formation of a cubic ZnSe phase and exhibited insignificant Zn3OH formation along with Zn3Se binding energies for both the films. UV–vis study showed that the band gap energies of ZnSe thin films prepared using HH and Na3-citrate were 3.1eV and 2.9eV, respectively. These investigations show that ZnSe thin films could be grown with good optical, structural, chemical, and compositional characteristics without using a toxic HH complexing agent.

Influence of Deposition Parameters on the Morphology, Structural, and Optical Properties of ZnSe Nanocrystalline Thin Films

Zinc selenide (ZnSe) nanocrystalline thin films were prepared by using chemical bath deposition at different ammonia concentrations and different deposition temperatures. The structural and optical properties of ZnSe nanocrystalline thin films were investigated as a function of the ammonia concentration in precursors or the deposition temperature using scanning electron microscopy, energy-dispersive spectrometry, x-ray diffraction measurements, and ultraviolet (UV)–visible spectrophotometry measurements. The results reveal that the ZnSe thin films are composed of a large number of uniform spherical particles. Each spherical particle contains several nanocrystals 5 nm to 7 nm in crystallite size. An increase in both the average diameter of the spherical particles and the crystallite size of the nanocrystals occurs with an increase in ammonia concentration and/or deposition temperature. The Se/Zn atom ratios in the ZnSe thin films increase and the optical band gaps, E g, of the ZnSe thin films decrease with an increase in ammonia concentration or deposition temperature. The kinetics and reaction mechanism of the ZnSe nanocrystalline thin films during deposition are discussed.

Investigation on the structure and optical properties of chemically deposited ZnSe nanocrystalline thin films

ZnSe thin films are deposited onto glass substrates by the chemical bath deposition (CBD) method at different hydrazine hydrate concentrations and different zinc sulfate concentrations using the precursors of zinc sulfate, sodium selenosulphate, hydrazine hydrate, ammonia and de-ionized water. The morphology, structural and optical properties of ZnSe nanocrystalline thin films were investigated as a function of hydrazine hydrate concentration or zinc sulfate concentration using scanning electron microscopy (SEM), X-ray diffraction (XRD) and UV–visible spectrophotometer measurements. The results reveal that the ZnSe thin films are composed of a large number of uniform spherical particles. The crystal structure of ZnSe nanocrystalline thin films is the zinc-blende structure. Both the average diameter of the spherical particles and the grain size of the nanocrystals increase with an increase in hydrazine hydrate concentration and/or zinc sulfate concentration. The optical band gap of the ZnSe thin films decrease with an increase in hydrazine hydrate concentration and/or zinc sulfate concentration due to the quantum-size effects. The kinetics and reaction mechanism of the ZnSe nanocrystalline thin films during deposition are discussed.

Nanocrystalline ZnSe thin films prepared by solution growth technique for photosensor application

Zinc selenide (ZnSe) thin films were deposited onto the glass substrates by solution growth technique (SGT). Triethanolamine (TEA) was used as a complexing agent for uniform deposition. Deposition parameters were optimized and elemental composition was confirmed by energy dispersive X-ray analysis technique (EDAX). The SEM, AFM and XRD pattern revealed that as-deposited thin films were uniformly deposited by nanocrystalline grains distributed over the entire glass substrate. Transmission spectra showed high transmission (∼55%) with direct optical band gap energy equal to 2.71eV. The I–V characteristic showed good photoresponse, suitable for photosensor applications.

ZnSe nanocrystalline thin films deposition on Si substrate by thermionic vacuum arc

ZnSe nanocrystalline thin films were deposited on Si wafer using thermionic vacuum arc (TVA) method. For the first time, binary semiconductor thin films were deposited by TVA. The microstructure and surface morphology of the ZnSe nanocrystalline thin films were investigated using X-ray diffractometry, scanning electron microscopy, energy-dispersive X-ray spectrometry, and atomic force microscopy (AFM). Grain dimensions and grain size were determined by AFM measurement. Moreover, spectroscopic ellipsometer was used to characterize the refractive indices of ZnSe nanocrystalline thin film. According to experimental measurement, ZnSe nanocrystalline thin film was polycrystalline with (1 1 1), (2 2 0), and (3 1 1) preferred orientations. Refractive indices were approximately 2.50 in all visible ranges. Our results show that nanocrystalline thin films can be deposited with TVA method.

Electrical characterization of nanocrystalline zinc selenide thin films

In the present paper, we have studied the effect of photo-illumination on electrical properties of nanocrystalline ZnSe thin films. The ZnSe thin films with different grain sizes (coherently diffracting domains) have been prepared. The semiconducting material with the composition Zn25Se75 has been prepared using melt-quenching technique. Thermal evaporation technique has been used to prepare nanocrystalline ZnSe thin films on highly cleaned glass substrates at different partial pressures of Ar gas. The grain size has been controlled by the partial pressure of inert gas. The grain size has been calculated using X-ray diffraction plots. Mobility activation has been studied from the photocurrent decay curves. The effective density of states (Neff), frequency factor (S), and trap depth (E) have been calculated for all the films having different grain sizes. Three different types of trap levels have been found in these films. There is a linear distribution of traps having different energies below the conduction band. The increase in photoconductivity is explained in terms of built in potential barriers (ϕb) at the grain boundaries.

Impact of various irradiation photon energies and gamma doses on the optical properties of ZnSe nanostructure thin film

ZnSe thin films were prepared by thermal evaporation technique under high vacuum (10−6 Torr) at 300 K and different film thickness. The structure of thin films was measured using grazing incident in-plane X-ray diffraction (GIIXD) and shows single phase zinc blende structure. The particle sizes of the deposited films were estimated for low film thickness by TEM and high film thickness by GIIXD. The particle size of ZnSe films was decreased from ~8.53 to 3.93 nm as film thickness lowered from 200 to 20 nm which ensures the nanocrystalline structure. The optical transmission (T) and reflection (R) in the wavelength range 190–2,500 nm for irradiated and unirradiated ZnSe thin films under investigation were measured. The effect of irradiation of different energies in range (0.1–1.25 MeV) from X-ray, 137Cs and 60Co irradiation sources were studied for ZnSe thin films of 100 and 200 nm thicknesses. The dependence of the absorption spectra and refractive index were investigated for different energies irradiation sources. The ZnSe films show direct allowed interband transition. The effect of particle size of nanocrystalline ZnSe thin films for unirradiated and irradiated by gamma (γ) doses from 137Cs on the optical properties was studied. Both the optical energy bandwidth and absorption coefficient (α) were found to be (γ) dose dependent.

Influence of gamma radiation on the optical properties of ZnSe nanocrystalline thin films

The effect of gamma (γ) irradiation on the absorption spectra and the optical energy bandwidth of ZnSe nanocrystalline thin films have been studied. Thin films of different thicknesses from 20 to 120 nm were deposited by Inert gas condensation technique at constant temperature of 300 K and under pressure 2 × 10−3 Torr of Argon gas flow. The optical transmission (T) and optical reflection (R) in the wavelength range 190–2,500 nm of ZnSe nanocrystalline thin films were measure for unirradiated and irradiated films. The dependence of the absorption coefficient α on photon energy hν was determined for different γ-doses irradiated films. The ZnSe thin films show direct allowed interband transition by γ-doses. Both the absorption coefficient (α) and optical energy bandwidth were found to be γ-dose dependent. The optical energy band width has been decreased by irradiated of γ-doses. The Egn values of irradiated thin films by 34.5 Gy of γ-doses were recovered to nearly their initial values after 100 days at 300 K.

Use of modified chemical route for ZnSe nanocrystalline thin films growth: Study on surface morphology and physical properties

The zinc selenide thin films have been deposited using modified chemical bath deposition (M-CBD) method. Zinc acetate and sodium selenosulphate were used as Zn 2+ and Se 2− ion sources, respectively. The preparative parameters such as concentration, pH, number of deposition cycles have been optimized in order to deposit ZnSe thin films. The as-deposited ZnSe thin films are specularly reflective and faint yellowish in color. The as-deposited ZnSe films are annealed in an air atmosphere at 473 K for 2 h. The films are characterized using structural, morphological, compositional, optical and electrical properties.

Pulsed laser deposition of nanocrystalline ZnSe:N thin films

We have grown nanocrystalline ZnSe thin films on GaAs(100) substrates by pulsed laser deposition using a KrF excimer laser. Atomic force microscopy shows that the ZnSe thin films grown on GaAs(100) at 10−1 Torr are flat and dense and are composed of crystallites with an average roughness of 1–2 nm. X-ray diffraction results indicate that crystallites of these ZnSe thin films are of (100) crystalline orientation with an average size of about 10–30 nm. X-ray photoelectron spectroscopy indicates that the as-deposited thin films contain 5–7% [N], and nitrogen with N–Zn bondings includes about 40–60% of the total contained nitrogen. Photoluminescence measurements show a donor-to-acceptor pair recombination emission, which reveals the activation of [N] atoms as shallow acceptors in nanocrystalline ZnSe.