Chalcogenide Glass Thin Films Research Articles

Erbium-doped chalcogenide glass thin film on silicon using femtosecond pulsed laser with different deposition temperatures

The properties of Er3+-doped gallium lanthanum sulphide thin films prepared on a silicon substrate by femtosecond pulsed laser deposition were studied as a function of process temperature. The films were characterised using transition electron microscopy imaging, X-ray diffractometry, Raman spectroscopy, fluorescence spectroscopy, and UV–Vis–NIR spectroscopy. The results show that by increasing the substrate temperature, the deposited layer thickness increases and the crystallinity of the films changes. The room temperature photoluminescence and lifetimes of the 4I13/2→4I15/2 transition of Er3+ are reported in the paper.

Ultralow Dispersion Multicomponent Thin-Film Chalcogenide Glass for Broadband Gradient-Index Optics.

A novel photothermal process to spatially modulate the concentration of sub-wavelength, high-index nanocrystals in a multicomponent Ge-As-Pb-Se chalcogenide glass thin film resulting in an optically functional infrared grating is demonstrated. The process results in the formation of an optical nanocomposite possessing ultralow dispersion over unprecedented bandwidth. The spatially tailored index and dispersion modification enables creation of arbitrary refractive index gradients. Sub-bandgap laser exposure generates a Pb-rich amorphous phase transforming on heat treatment to high-index crystal phases. Spatially varying nanocrystal density is controlled by laser dose and is correlated to index change, yielding local index modification to ≈+0.1 in the mid-infrared.

Solution phase driven As2S3 chalcogenide films: Optical and picosecond nonlinear optical properties

We demonstrate the fabrication and nonlinear optical (NLO) characterization of chalcogenide glass thin films obtained from the solution phase driven approach. The characterization of the films was ahieved using FESEM, AFM, micro-Raman, FTIR, UV-Visible spectroscopy, optical profilometry and XRD. The NLO studies were performed on the solution driven and thermally deposited As2S3 films with [Formula: see text]2[Formula: see text]ps, 800[Formula: see text]nm laser pulses using the Z-scan technique. The results obtained from AFM measurements demonstrated that the surface roughness of the film was considerably low ([Formula: see text]2[Formula: see text]nm) and Z-scan data indicated that the nonlinear refractive index was in the 1.0–[Formula: see text][Formula: see text]m2/W range.

Thermal dependence of photo-induced effects in spin-coated As20Ge12.5S67.5 thin films

Chalcogenide glass thin films of ternary As20Ge12.5S67.5 composition were prepared in specular quality using spin-coating technique from n-butylamine based glass solution. The content of organic residuals was notably reduced by post-deposition thermal treatment. The annealing process induced significant structural changes resulting in thin films with the structure close to the source bulk glass. The thickness of deposited thin films was decreasing with increasing annealing temperature. Contrary, the refractive index, optical bandgap, roughness and chemical stability were increasing. The experimental data also proved that deposited thin films were photo-sensitive as opto-physical properties and chemical resistance were changed after UV light exposure. The exposed thin films annealed bellow 90°C were etched slower than unexposed ones (negative etching) and the thin films annealed above 90°C were etched faster (positive etching).

Optical characterization of amine-solution-processed amorphous [formula omitted] chalcogenide thin films by the use of transmission spectroscopy

Amorphous thin layers with non-stoichiometric chemical composition As33S67 (AsS2) have been prepared by spin coating. This particular deposition technique is a very promising, low-cost technique, to create optical-grade, chalcogenide glass thin films, which are certainly ideal for visible and infrared applications. The layer thickness and optical constants have been first determined by the Swanepoel transmittance-envelope method, for the case of uniform thin films, with an accuracy better than 1%. The refractive-index dispersion has been analyzed on the basis of the Wemple-DiDomenico single-effective-oscillator model: n2(E)=1+E0Ed/(E02−E2), where E0 is the single-oscillator energy and Ed the dispersion energy. The strong-absorption region of the absorption edge is described using the ‘non-direct electronic transition’ model, proposed by Tauc. Structural information of the AsS2 bulk and thin-layer samples has been gained from X-ray diffraction measurements, and, also, from the analysis of the refractive-index dispersion. In addition, the simulation software WVASE32 was successfully utilized in fitting the experimental, normal-incidence transmission data by the use of Tauc-Lorentz model; an excellent fit between the measured and software-generated optical transmission spectra has been generally achieved, with a mean-squared-error as low as around 0.4.

Electrospray deposition of quantum dot-doped Ge23Sb7S70 chalcogenide glass films

The incorporation of quantum dots (QDs) into chalcogenide glass films is attractive for their luminescent properties. Such QD-doped glass structures could serve as a compact, on-chip light source for planar photonic devices. Typical processing methods such as spin coating have limitations of excessive material waste, little control on the pattern of the film and difficulty for scale-up. To overcome these limitations, this study introduces electrospray as a more versatile processing method and has deposited QD-doped chalcogenide glass thin films. The parameters of the electrospray process are prudently chosen to ensure one or none QD is enclosed per liquid droplet. The transmission electron microscopy imaging of resultant films confirm enhanced QD dispersion with reduced aggregations. Absorption and photoluminescence characterization shows the QD-doped chalcogenide glass films prepared by electrospray maintain signature spectra of QDs from the manufacturer.

Influence of annealing on the optical properties, structure, photosensitivity and chemical stability of As30S70 spin-coated thin films

Chalcogenide glass (ChG) thin films prepared by solution based deposition technique offer important advantages over vacuum deposited films, which are useful for many applications especially in infrared optics. Their fabrication, which comprises dissolving the ChG in volatile organic solvent and then depositing thin film by spin coating the solution, is simpler and significantly cheaper. However, contaminants from the solvent are incorporated. The residual organic content in the films is significantly reduced by appropriate thermal treatment. This work reports the influence of specific annealing conditions and UV light exposure on the structure, opto-physical and chemical properties of As30S70 spin-coated ChG films. The results show increase in refractive index with increasing annealing temperature, whereas the thickness and optical bandgap decrease. The UV exposed regions of the samples exhibit positive etching in amine based solvents. The HS-LEIS spectroscopy is used to determine the elemental concentration profile of annealed thin film, which shows almost stable As/S ratio with composition close to that of the source bulk glass. Thus UV light induced structural changes and the mechanism of selective etching are proposed.

Recent developments on the optical properties of thin films of chalcogenide glasses

Chalcogenide glasses (ChG) has emerged as important materials due to their potential applications in infrared optics for communication, imaging, limiting, remote sensing and laser power delivery etc. Examining ChG for their various applications, different properties of these were under immense investigation by various researchers from nearly every part of the world. Study of ChG for optical properties like optical band gap and refractive index are the backbone while considering them for applications. The present review focuses on the optical properties of various binary, ternary and quaternary chalcogenide systems. Subsequently applications and future prospects of ChG have been sketched. The attracting prospective applications have drive us to put the review on optical properties of chalcogenide thin films both comprehensive and expedient to new as well as established researchers in this area.

Structural features of spin-coated thin films of binary AsxS100 − x chalcogenide glass system

Spin-coating technology offers a convenient method for fabricating photostable chalcogenide glass thin films that are especially attractive for applications in IR optics. In this paper we report the structure of spin-coated AsxS100−x (x=30, 35, 40) thin films as determined using high resolution X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy, especially in relation to composition (i.e. As/S ratio) and preparation process variables. It was observed that As atoms during preparation have a tendency to precipitate out in close to stoichiometric compositions. The mechanism of bonding between the inorganic matrix and organic residuals is discussed based on the experimental data. A weak interaction between S ions and amine-based clusters is proposed as the basis of structural organization of the organic–inorganic interface.

Light-induced metastable defects in a-Se90X10 (X = Sb, In and Ag) thin films

Thin films of chalcogenide glasses in a binary system of Se90X10 (X = Sb, In and Ag) have been prepared by the vacuum evaporation technique. Thermally stimulated current measurements have been made to find out the trap density in these materials. To study light-induced defects in these materials, white light of intensity 1200 lux is shown on the amorphous films in vacuum for different exposure times. It is observed that the density of traps increases with exposure time, indicating the appearance of light-induced metastable defects in these materials.

Fabrication of stable, low optical loss rib-waveguides via embossing of sputtered chalcogenide glass-film on glass-chip

We report low-loss, single-mode rib optical waveguides on-chip, fabricated using hot-embossing for the first time of radio-frequency sputtered \(\hbox {As}_{2}\hbox {Se}_{3}\) chalcogenide-glass thin films on a chalcogenide-glass substrate. Waveguides 4–6 \(\upmu \hbox {m}\) wide and \(1.9 \pm 0.1~\upmu \hbox {m}\) high are fabricated. Waveguide optical loss, using the Fabry–Perot technique, which is known to over-estimate loss, is found to be \(<\)0.78\(\hbox { dB cm}^{-1}\) for the TE mode, and \(<\)0.81 \(\hbox {dB cm}^{-1}\) for the TM mode, at 1,550 nm wavelength. Glass stability of the chalcogenide rib waveguides is excellent and is discussed in relation to the results of others.

Pulsed laser deposition of rare-earth-doped gallium lanthanum sulphide chalcogenide glass thin films

Amorphous chalcogenide thin films are of high current interest for technological applications as optical storage media or waveguides for photonic integrated circuits. As part of a larger project including fs, ps and ns pulsed laser deposition regimes, Er- and Pr-doped GLS thin films were deposited by ns PLD, and their structural, chemical and optical properties were analyzed by optical and electronic microscopy, stylus profilometry, X-ray diffraction, Raman spectroscopy, time-of-flight secondary ion mass spectrometry (TOF–SIMS), energy-dispersive X-ray spectroscopy, variable-angle spectroscopic ellipsometry and optical transmission. Films deposited at moderate fluence (~4 J/cm2) in UV (266 nm) presented a good surface quality, while exhibiting acceptable composition uniformity and deviations from stoichiometry in line with the literature. Composition and optical properties dependences on the deposition conditions were investigated and discussed with respect to previous studies on similar systems.

New functionality of chalcogenide glasses for radiation sensing of nuclear wastes

Data about gamma radiation induced effects in Ge40Se60 chalcogenide thin films and radiation induced silver diffusion within these are presented. Blanket films and devices were created to study the structural changes, diffusion products, and device performance. Raman spectroscopy, X-ray diffraction, current vs. voltage (I–V) and impedance measurements expound the behavior of Ge40Se60 glass and silver diffusion within this glass under radiation. Raman study shows that there is a decrease in the area ratio between edge shared and corner shared structural units revealing structural reorganization occurring in the glasses as a result of gamma radiation. X-ray diffraction studies revealed that with sufficiently radiation dose it is also possible to create Ag2Se in selenium-depleted systems. Oxidation of the Ge enriched chalcogenide backbone is confirmed through the electrical performance of the sensing elements based on these films. Combination of these structural and diffusion products influences the device performance. The I–V behavior is characterized by increase in current and then stabilization as a function of radiation dose. Additionally, device modeling is also presented using Silvaco software and analytical methods to shed light on the device behavior. This type of sensor design and material characterizations facilitate in improving the radiation sensing capabilities of silver containing chalcogenide glass thin films.

Nucleation and growth in amorphous (GeS2)0.9(Sb2S3)0.1 thin films

The rates of isothermal nucleation and growth in chalcogenide glass thin films of (GeS2)0.9(Sb2S3)0.1 were studied using optical microscopy. Nucleation data was obtained from double stage heat treatment, followed by image analysis of polarized optical micrographs. The applicability of classical nucleation theory (CNT) to the nucleation data has been discussed. The growth data, corrected for viscosity suggest interface controlled 2D nucleated growth of β-GeS2 crystals. The isothermal curves of nucleation and growth determined by CNT and 2D nucleated growth model, respectively were found to be weakly intersecting. The nucleation curve had maxima at 350°C, which is below the glass transition temperature, while the growth curve had a peak at 439°C.

Large Area IR Microlens Arrays of Chalcogenide Glass Photoresists by Grayscale Maskless Lithography

The ability to use chalcogenide glass thin films as photoresists for one-step maskless grayscale lithographic patterning is demonstrated. It is shown that the chalcogenide photoresists can be used to fabricate grayscale patterns with smooth and continuous profiles such as arrays of cylindrical and spherical microlenses, which are useful as optical structures for IR applications. The etching and exposure parameters are optimized to obtain smooth reproducible lens arrays of 150 μm periodicity and up to ∼170 nm height on large areas (∼1 cm(2)). The roughness is found to increase as a function of the exposure dose and is attributed to the selective dissolution of the As-Se, As-As, and Se-Se bonds present in the nanodistributed phases and the presence of the oxide phase. Thus, a minimum exposure dose produces optimally patterned lens arrays. The focal length calculated for the smooth microlens array is ∼9.3 mm, indicating the suitability of the lens arrays for focusing applications in the IR region.

Electronic and atomic structure of amorphous thin films with high-resolution XPS: Examples of applications & limitations

The use of high resolution X-ray photoelectron spectroscopy to study chalcogenide glass thin films is analyzed. It is shown that the method is an effective tool to explore different chemical environments in the films and control chemical composition of the surface. Examples of the method applications such as kinetics study of induced silver dissolution in the thin films and investigation of oxidation on the surface of the thin film are presented. Limitations of the method are shown on the example of photoinduced structural transformations in chalcogenide glass thin films.

Electron irradiation induced reduction of the permittivity in chalcogenide glass (As2S3) thin film

In this paper, we investigate the effect of electron beam irradiation on the dielectric properties of As2S3 chalcogenide glass. By means of low-loss electron energy loss spectroscopy, we derive the permittivity function, its dispersive relation, and calculate the refractive index and absorption coefficients under the constant permeability approximation. The measured and calculated results show a heretofore unseen phenomenon: a reduction in the permittivity of ≥40%. Consequently a reduction of the refractive index of 20%, hence, suggests a conspicuous change in the optical properties of the material under irradiation with a 300 keV electron beam. The plausible physical phenomena leading to these observations are discussed in terms of the homopolar and heteropolar bond dynamics under high energy absorption. The reported phenomena, exhibited by As2S3-thin film, can be crucial for the development of photonics integrated circuits using electron beam irradiation method.

Study of As50Se50 Thin Film Dissolution Kinetics in Amine based Solutions

Abstract Chalcogenide glass thin films are suitable materials for micro optical elements fabrication due to their convenient physical and chemical properties. They are generally photosensitive and thus can be selectively etched. Therefore they can be exploited as photoresists in photolithography. In this paper we deal with the study of As 50 Se 50 thin films dissolution kinetics in EDA based solutions. The detailed evolution of the etching curves is discussed and the dependences of the average etching rate on the composition and temperature of the etching bath are described.

Optical Properties of Thin Films of Ga&lt;SUB&gt;15&lt;/SUB&gt;Se&lt;SUB&gt;75&lt;/SUB&gt;Ag&lt;SUB&gt;10&lt;/SUB&gt; Chalcogenide Glasses Before and After Laser Irradiation

Thin films of chalcogenide glasses of Ga15Se75Ag10 with thickness 4000 A were prepared by thermal evaporation technique. The amorphous nature of Ga15Se75Ag10 glasses and thin films was verified by Differential Scanning Calorimeter (DSC) and X-ray diffractometer. The surface microstructure of amorphous and laser irradiated thin films w re examin d by scanning electron microscope (SEM). The changes in optical properties due to the influence of laser radiation on amorphous thin films of Ga15Se75Ag10 glassy alloy were calculated from absorbance spectra as a function of photon energy in the wave length region 300–900 nm. Analysis of the optical absorption data shows that the rule of non-direct transitions predominates. It has been observed that laser-irradiation of the films leads to a decrease in optical band gap while increase in absorption coefficient and extinction coefficient. The decrease in the optical band gap is explained on the basis of change in nature of films, from amorphous to polycrystalline state.

Monitoring structural phase transition of (Ge 2S 3) x(As 2S 3) 1−x chalcogenide glass with Raman spectroscopy

Chalcogenide glass thin films (Ge 2S 3) x (As 2S 3) 1− x , with x = 0.3, 0.5, 0.7, and 0.9, were prepared by flash thermal evaporation of glass powders on c-Si substrate. We have investigated their structural properties for different average coordination numbers Z = 2.52, 2.6, 2.68 and 2.78. Structural changes were monitored by Raman scattering with two different excitation lines, λ = 1064 nm and λ = 514.5 nm. Recorded spectra confirmed that structural changes of the samples are connected with the change of average coordination number. Shift between spectra recorded with two different excitation lines is observed. The shift was discussed in terms of structural ordering at the threshold Z and its connection with the band-tail states.