As2Se3 Film Research Articles

Влияние коронного разряда на оптические свойства тонкопленочных структур Cu-As-=SUB=-2-=/SUB=-Se-=SUB=-3-=/SUB=-

Effect of corona discharge on holographic recording of diffraction gratings in Cu-As2Se3 thin film structure was studied. Thin film structures of Cu-As2Se3 were prepared on glass substrates by sequential deposition of Cu and As2Se3 layers using vacuum thermal evaporation technique. Applying of negative corona discharge during recording procedure caused an enhancing both of the holographic sensitivity and diffraction efficiency of the grating. Exposure to actinic light illumination resulted in photodarkening effect in Cu-As2Se3 thin film structure in the spectrum region of strong absorption. At the same time the fotoinduced bleaching of Cu-As2Se3 film structure in the spectrum region of weak absorption was observed. Negative corona discharge applied during the light exposure enhanced the bleaching, while positive corona discharge caused its weakening. The photoinduced diffusion of Cu+ ions into As2Se3 film was considered to explain qualitatively the experimental results.

Optical and photoluminescence performance of electrodeposited arsenic selenide thin film doped with erbium ion

The solid state performance of Erbium ion (Er3+), a rare-earth ion, incorporated into the lattice of arsenic selenide (As2Se3) film is here presented. By varying the concentration of the dopant from 1 to 5% (wt.%), the films were deposited on a fluorine-doped SnO2 glass via the electrodeposition method. The structural, optical and morphological characteristics of the samples were obtained using the XRD and Raman spectroscopy, UV-VIS-NIR and photoluminescence spectroscopy and scanning electron microscopy respectively. Polycrystalline films having monoclinic and cubic crystal structures for the undoped and doped samples respectively were observed from the XRD analysis. 34.5 nm and 44.2 nm were estimated for the mean grain size of the undoped and doped films respectively. The Raman spectra revealed the diffusion of the Erbium ion (Er3+) into the As2Se3 lattice by Raman shift. The films revealed least absorbance and high transmittance up to 99% in the IR region with increasing doping. A high refractive index value of 2.66 was observed for all the films with a broadening towards the NIR region. The energy bandgap was estimated and lies in the range of 3.61–3.85 eV which slightly decreased with increasing doping concentration. The PL spectra showed intense excitonic (near-edge) emission bands at 348 nm with increasing doping. SEM micrographs revealed fairly homogeneous nano-ball morphology at lower doping concentration and nanoclusters at higher doping concentration. Annealing of the films above the glass-transition temperature (Tg) allowed the transition of the film to the crystalline phase which is an interesting feature in binary chalcogenide-based phase change memory (PCM) photonics devices.

Pseudodielectric Dispersion in As2Se3 Thin Films

Herein, X‐ray diffraction, energy dispersive X‐ray spectroscopy, and spectral ellipsometry techniques are used to investigate the structural, pseudo‐optical, and pseudodielectric properties of arsenic selenide thin films. The stoichiometric films which are prepared by the thermal evaporation technique are found to prefer the amorphous nature of growth. While the pseudoabsorption coefficient spectra display strong absorption bands at 1.84, 1.81, 1.41, and 1.13 eV, the preferred pseudo‐optical transitions happen within a direct forbidden energy bandgap of 1.80 eV. In addition, the real part of the pseudodielectric spectra displays three strong resonance peaks at critical energy values of 2.33, 1.90, and 1.29 eV. Modeling of the imaginary part of the pseudodielectric constant spectra in accordance with the Drude–Lorentz approach results in the existence of six linear oscillators. The response of arsenic selenide to elliptically polarized light signals shows that the films exhibit drift mobility, free electron concentration, and plasmon frequency values in the ranges of 0.21–43.96 cm2 V−1s−1, 1.90–58.0 × 1019 cm−3, and 5.8–32.0 GHz, respectively. The optical conductivity parameters for As2Se3 film nominate it as a promising candidate for the fabrication of tunneling diodes suitable for microwaves filtering up to 32.0 GHz and as thin‐film transistors.

Structural and optical study of Zn-doped As2Se3 thin films: Evidence for photoinduced formation of ZnSe nanocrystallites

Amorphous Zn-doped As2Se3 films with a nominal zinc content x up to 10 at.% were prepared by thermal evaporation. Their structure is characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray photoemission spectroscopy (XPS), and Raman spectroscopy. The AFM data show a considerable increase of the film surface roughness for films with x > 5 at.%. A strong gradient of the Zn content decreasing into the film depth is confirmed by the EDX and XPS data. Heavily Zn-doped (above 7 at.%) As2Se3 films reveal photostructural changes in the course of the Raman measurements. New Raman features are attributed to TO and LO vibrations of ZnSe nanocrystallites formed in the film under laser illumination. Depending on the laser wavelength and power density, the ZnSe nanocrystallites can experience tensile strain in the film due to a non-thermal photoplastic effect in the As2Se3 film resulting in a partial removal of the material from the laser spot. The tensile strain value, estimated from the TO and LO phonon frequency shift, is shown to reach up to 2.9 GPa.

In-doped As2Se3 thin films studied by Raman and X-ray photoelectron spectroscopies

Amorphous In-doped As2Se3 films with nominal indium contents x up to 7 at.% were prepared by thermal evaporation. Atomic force microscopy studies confirm the uniform film structure with a surface roughness near 5 nm, noticeably higher than for similarly prepared undoped As2Se3 film. X-ray photoelectron spectroscopy (XPS) studies enabled the chemical composition of the films to be examined. As follows from the XPS data, the In content in the film strongly decreases with the film depth. For films with x ≥ 2 at.%, Raman features attributed to transverse and longitudinal optical phonons of InAs are revealed in the Raman spectra as an evidence for the formation of InAs nanocrystallites in the As2Se3:In film under laser illumination.

An in situ Study of the Kinetics of a Solid-Phase Reaction Activated by the Energy of Elastic Stresses Arisen upon the Formation of the Cu/As2Se3 Nanosized Film Structure

For the first time, the kinetics of a solid-phase chemical reaction activated by the energy of elastic stresses generated upon the formation of the Cu/As2Se3 nanosized film structure is investigated in situ. It is shown that the time at which a solid-phase chemical reaction starts, as well as the voltage of the Cu/As2Se3 heterolayer, significantly depends on the thickness of the As2Se3 film. At a critical thickness of the As2Se3 film, which is equal to 110 nm, a threshold value of the energy of elastic stresses is achieved. Relaxation of this energy over new defects (micropores and microcracks) generated in the film system leads to the activation of a solid-phase chemical reaction and an increase in its rate. A mechanism of the operation of a positive feedback between the chemical reaction in a solid phase and elastic stresses is proposed.

Photo- and thermally induced property change in Ag diffusion into Ag/As2Se3 thin films

In the present report, we have prepared As2Se3 and bilayer Ag/As2Se3 chalcogenide thin films prepared by thermal evaporation process. The top Ag layer is being diffused into the bottom As2Se3 layer by 532 nm laser irradiation and thermal annealing process. The photo and thermal energy drives the Ag+ ions into the As2Se3 matrix that enhances the formation of As–Se–Ag solid solution which shows the changes of optical properties such as transmission, absorption power, refractive index, and optical band gap. The transmission power drastically decreased for the thermal-induced film than the laser induced one; and the reverse effect is seen for the absorption coefficient. The non-linear refractive index is found to be increased due to the Ag diffusion into As2Se3 film. The indirect allowed optical band gap is being reduced by a significant amount of 0.17 eV (thermal diffusion) and 0.03 eV (photo diffusion) from the Ag/As2Se3 film. The Ag diffusion creates chemical disorderness in the film observed from the two parameters which measures the degree of disorder such as Urbach energy and Tauc parameter. The structural change is not noticed in the studied film as seen from the X-ray diffraction pattern. Scanning electron microscopy and atomic force microscopy investigations showed that the surface morphology was influenced by the diffusion phenomena. The change in optical constants in such type of film can be used in optical waveguides and optical devices.

Formation of CdSe nanocrystals in Cd-doped thin arsenic selenide films under laser irradiation

Amorphous Cd-doped As2Se3 films with nominal Cd contents up to 12at.% were prepared by thermal evaporation. Atomic force microscopy studies confirm the uniform film structure with surface roughnesses below 1nm, independent of the Cd content. As shown by energy-dispersive X-ray spectroscopy, the Cd content in the film reveals a strong gradient and decreases with the film depth. For heavily Cd-doped (above 7at.%) As2Se3 films, Raman features attributed to CdSe longitudinal optical (LO) phonon and its overtone (2LO) are revealed in the Raman spectra as an evidence for the formation of CdSe nanocrystallites in the As2Se3:Cd film under above-bandgap or below-bandgap laser illumination. The CdSe nanocrystallites undergo tensile strain due to a photoplastic effect in the As2Se3 film, i. e. partial removal of the material from the laser spot. The tensile strain value, estimated from the LO phonon frequency shift, is shown to reach nearly 2GPa.

Laser induced optical properties change by photo diffusion of Sb into As2Se3 chalcogenide thin films

The present study reports the effect of Sb deposition onto As2Se3 film and its subsequent photo diffusion into As2Se3 matrix by 532nm laser. The bilayer Sb/As2Se3 contains Sb as active, optical absorbing and diffusing layer and As2Se3 as barrier layer. The chemical composition and amorphous nature of the as-prepared thin films were examined by energy dispersive X-ray analysis and X-ray diffraction (XRD) respectively. Optical parameters such as transmitivity, absorption coefficient, optical gap, Urbach energy of the studied thin films were studied by absorption spectroscopy. The mechanism of optical absorption follows the rule of indirect allowed transition model proposed by Tauc. It is observed that after photo diffusion, there is a shift of the optical absorption edge to higher photon energy. The absorption of high energy photons enhances the creation of homopolar bonds due to diffusion which increases the density of defect states. The decrease of optical band gap with the addition of Sb to As2Se3 has been explained on the basis of density of states and the increase in disorder in the system. The X-ray photoelectron spectroscopy measurements show the different bonding behavior due to photo induced diffusion. This type of change is generally irreversible in nature which can be used for optical recording purpose.

Тонкие пленки бинарных халькогенидов As2 X3 (X = S, Se), полученные методом спин-коатинга

This paper describes the processes of preparing solutions of binary vitreous semiconductor materials As2X3 (X = S, Se) and fabricating thin films based on them by spin coating. The initial materials are synthesized using semiconductor purity grade solvents by the direct synthesis in pre-vacuumed quartz vials at a maximum temperature of 750oС and identified by the authors as glass. The obtained amorphous thin films are proven to have an island morphology. The thickness of the As2S3 film can vary in the range of 200 nm (at an average roughness of 0.7 nm) to 2.5 μm (at an average roughness of 100 nm). The thickness of the As2Se3 film can vary in the range of 200 nm (at an average roughness of 8 nm) to 3 μm (at an average roughness of 200 nm). The optical characteristics of thin films are also studied, in particular optical transmission in the visible spectrum. The band gap of the obtained films is determined by employing a Tauc plot. The findings of the experiment are compared with the literature data.

Optical properties change in laser-induced Te/As2Se3 chalcogenide thin films

In the present work, we report the change in optical parameters due to the deposition and photo-induced diffusion of Te layer into the chalcogenide As2Se3 film. The photo-diffusion creates a solid solution of As–Se–Te which has potential application in optical devices. The Te/As2Se3 bilayer films prepared by thermal evaporation technique were studied by various experimental techniques. The photo-diffusion of Te into As2Se3 matrix was done by 532-nm laser irradiation. The structure of the As2Se3, as-prepared and irradiated Te/As2Se3 films was studied by X-ray diffraction which were amorphous in nature. The presence of all the elements was checked by energy-dispersive X-ray analysis, and the optical transmission spectra were recorded by Fourier transform infrared spectrometer. The optical band gap is reduced by the deposition and diffusion of Te into As2Se3 film which is due to the increase in density of defect states in the gap region. The transmission is decreased, whereas the absorption efficiency is increased with the increase in disorderness. The X-ray photoelectron spectroscopy carried out on these films gives information about the bonding change due to the photo-diffusion process. Therefore, this is an important result which will open up new directions for the application of this material in semiconducting devices.

Durability and photo-electric characteristics of a mille-feuille structured amorphous selenium (a-Se)–arsenic selenide (As2Se3) multi-layered thin film

A mille-feuille structured amorphous selenium (a-Se)–arsenic selenide (As2Se3) multi-layered thin film and a mixed amorphous Se–As2Se3 film is compared from a durability perspective and photo-electric perspective. The former is durable to incident laser induced degradation after numerous laser scans and does not crystallise till 105° of annealing, both of which are improved properties from the mixed evaporated film. In terms of photo-electric properties, the ratio between the photocurrent and the dark current improved whereas the increase of the dark current was higher than that of As2Se3 due to the unique current path developed within the mille-feuille structure. Implementing this structure into various amorphous semiconductors may open up a new possibility towards structure-sensitive amorphous photoconductors.

Study of the dynamics and mechanisms of deformation of thin chalcogenide As(Ge)2Se3 films by nanoindentation

The mechanical properties of As2Se3 and Ge2Se3 thin films have been studied by the method of quasi-static nonoindentation. The mechanisms of formation and recovery of the indentations in the studied materials have been analyzed under conditions of their local loading. It has been revealed that the deformation mechanism of the chalcogenide films changes in going from As2Se3 to Ge2Se3. It has been found that, during deformation of the As2Se3 film under the indenter, the accumulation of plastic deformation prevails, and, for the Ge2Se3 film, the substantial mechanism is the relaxation of its deformation.

Optical and structural properties of Ag(Cu)–As2Se3 chalcogenide films prepared by a photodoping

We prepared Ag(Cu)–As2Se3 films by step-by-step photodoping Ag (or Cu) into an evaporated As2Se3 film and determined their optical properties such as refractive index and band gap energy from the transmission spectrum of the sample. The highest concentration of the metal doped into the amorphous As2Se3 film was 21at.% for Ag and 7at.% for Cu. Moreover we performed Raman spectroscopy to obtain information about the local structure of the photodoped chalcogenide films. It has been found that there is a distinct difference in the optical properties between Ag–As2Se3 and Cu–As2Se3 films. The measured Raman spectra agree approximately with ones we previously obtained for bulk glasses. In our case, this agreement means that the successive photodoping used here produces nearly homogeneous chalcogenide films. It has also been found that a mixture of Se clusters (Se8 ring, Se12 ring, and Se4 chain) is formed near the surface of the photodoped Ag(Cu)–As2Se3 films.

Profiled hologram diffraction gratings based on As2Se3 inorganic photoresist

We devised a method of producing blaze hologram diffraction gratings by transforming symmetric grooves of the original grating into asymmetric ones using an additional oblique irradiation by monochromatic or polychromatic light and a repeated chemical etching of the additionally irradiated grating. Photosensitive As2Se3 film layers are used as a photoconductive material for recording gratings. A numerical computer modeling of the formation of asymmetric grooves is conducted. The calculated shape of the groove profile is in good agreement with experimental data. The manifestation of asymmetry of the profile shape of the produced gratings in angular and spectral relations for their diffraction efficiency is considered. It is shown that by varying the parameters of producing the original gratings and the conditions of their additional treatment it is possible to obtain hologram gratings with the required profile shape and blaze angle.

In-House Measurements of XAFS by Means of Total Reflection

We have developed a double channel-cut monochromator composed of two channel-cut Si(111) crystals, and obtained highly parallel and highly monochromatized X-ray beam. Reflectivity of an As2Se3 film on an Al substrate was measured as a function of photon glancing angle around the critical one of total reflection. The complex refractive index was determined so that the simulated Fresnel reflectivity fits the measured values. Since the imaginary part of the refractive index is correlated with the linear absorption coefficient, we can obtain XAFS spectrum by means of reflectivity measurements in house.

Acoustooptic interaction in a diffused waveguide with a dielectric film. II. Experiments

Experimental results are reported and these confirm a considerable increase in the efficiency of the acoustooptic interaction of TE and TM modes in a diffused waveguide coated by a dielectric (As2Se3) film characterized by a high refractive index. A method is suggested for the determination of the optical parameters of such coatings. A description is given of apparatus for the measurement of the coupling coefficient representing the acoustooptic interaction.

Electron-pulsed diffusion of Se in GaAs

n + regions with concentrations exceeding 1019 cm−3 have been formed in GaAs by pulse diffusion with an electron beam. The diffusion source is a deposited As2Se3 film which is removed by the pulse without unduly affecting the initial polished appearance of the GaAs. The resulting doped layers are characterized by exceedingly low carrier mobilities. The well-known similar deficiency of pulse-annealed implanted layers would thus appear to be caused by some artifact introduced by the pulse rather than by residual damage unannealed from the implantation. Pulse diffusion should provide an alternative means to implantation for forming n+ contacts in GaAs.

Optical spectra, relaxation, and energy transfer of Eu 3+ and Cr 3− in an europium phosphate glass

Amorphous Cd-doped As2Se3 films with nominal Cd contents up to 12 at.% were prepared by thermal evaporation. Atomic force microscopy studies confirm the uniform film structure with surface roughnesses below 1 nm, independent of the Cd content. As shown by energy-dispersive X-ray spectroscopy, the Cd content in the film reveals a strong gradient and decreases with the film depth. For heavily Cd-doped (above 7 at.%) As2Se3 films, Raman features attributed to CdSe longitudinal optical (LO) phonon and its overtone (2LO) are revealed in the Raman spectra as an evidence for the formation of CdSe nanocrystallites in the As2Se3:Cd film under above-bandgap or below-bandgap laser illumination. The CdSe nanocrystallites undergo tensile strain due to a photoplastic effect in the As2Se3 film, i. e. partial removal of the material from the laser spot. The tensile strain value, estimated from the LO phonon frequency shift, is shown to reach nearly 2 GPa.

The Influence of Moisture on the Storage Phenomenon in As2Se3 Evaporated Films

The influence of moisture on the persistence of photoconduction has been investigated on sandwich type cells with an evaporated As2Se3 film and two evaporated Al electrodes. While the phenomenon is observed in the cells prepared by moisture-free processes, no storage is observed in the cells with theelectrodes containing adsorbed water. Thus water is shown to plays an important role in the disappearance of the storage phenomenon.