Ge Se Glasses Research Articles

Optical transmittance range of High-Temperature stable phase germanium dichalcogenide (GeS2) single crystal grown by the Bridgman method

A high-temperature (HT) stable phase germanium dichalcogenide (GeS2) was grown in an evacuated quartz ampoule to investigate its transparency range. First, as a starting material for the crystal growth of HT-GeS2, GeS2 glass containing HT-GeS2 crystals was synthesized using our previously improved process for synthesizing polycrystalline sulfide compounds in a conventional horizontal furnace. The HT-GeS2 crystal was grown using the Bridgman method under a temperature gradient of 20–30 °C/cm. The grown HT-GeS2 single crystal was easily cleaved along the growth direction, and this cleaved surface was identified as the (001) face using X-ray diffraction (XRD). Single-crystal XRD analysis confirmed the growth of an HT-GeS2 single crystal with a monoclinic structure (space group P21/c) and lattice parameters of a = 6.7061(4) Å, b = 16.0877(13) Å, and c = 11.4242(11) Å, and β = 91.069 (8)°. The optical transmittance spectra of the HT-GeS2 single crystal were measured in the visible and infrared (IR) regions, revealing a transparency range of 0.36–22.5 μm. Differential thermal analysis revealed the melting point of HT-GeS2 as 841 ± 1 °C. The HT-GeS2 single crystal is expected to be a new candidate for IR optical crystal.

Reproducibility of the Optical Absorption Edge in Amorphous GeS2

Herein, poor reproducibility of optical absorption edges in GeS2 glasses and films is seen. Reported spectral positions of the absorption edge in melt‐quenched glasses spread over ≈0.2 eV at ħω ≈ 3 eV. In deposited films, the edge red‐shifts to ħω ≈ 2.5 eV showing wider variations of ≈1 eV. This work considers plausible reasons of such low, spectral reproducibility, with the aid of ab initio molecular orbital analyses of Ge–S clusters and known insights on optical gaps, electron‐spin‐resonance signals, and structural data. The variation in the glass is likely to be governed by several factors including compositional fluctuation, edge/corner‐shared configurations, wrong bonds, and intimate valence‐alternation pairs. The conspicuous red‐shift in the films seems to be affected also by neutral dangling bonds.

Defects in Se, As2S3, and GeS2 glasses: Ab initio analyses of related clusters

Dangling bonds in Se, As2S3, and GeS2 glasses and wrong bonds in the compounds have been comparatively studied using an ab initio molecular-orbital software. Defect energies and the densities in the chalcogenide glasses are estimated from the total energy Et of small clusters such as H-nSe-H, As3S4H, and Ge4S4H. Properties of corner- and edge-shared connections are also explored for the As-S and Ge-S systems. The three kinds of clusters show for a meta-stable energy ΔEt, relative to the total energy Et of normal bonding structures, a magnitude order of ΔEt(IVAP) < ΔEt(2D0) < ΔEt(D+/D−). Based on this result, we discuss why only GeS2 exhibits unpaired electron spins. The analysis also manifests that ΔEts of clusters containing wrong bonds (As-As, Ge-Ge, and S-S) are comparable with those of ΔEt(IVAP). Regarding electronic levels, the three glasses seem to possess marked gap states having different origins.

Structural and electronic transformations of GeSe2 glass under high pressures studied by X-ray absorption spectroscopy

Pressure-induced transformations in an archetypal chalcogenide glass (GeSe2) have been investigated up to 157 GPa by X-ray absorption spectroscopy (XAS) and molecular dynamics (MD) simulations. Ge and Se K-edge XAS data allowed simultaneous tracking of the correlated local structural and electronic changes at both Ge and Se sites. Thanks to the simultaneous analysis of extended X-ray absorption fine structure (EXAFS) signals of both edges, reliable quantitative information about the evolution of the first neighbor Ge-Se distribution could be obtained. It also allowed to account for contributions of the Ge-Ge and Se-Se bond distributions (chemical disorder). The low-density to high-density amorphous-amorphous transformation was found to occur within 10 to 30 GPa pressure range, but the conversion from tetrahedral to octahedral coordination of the Ge sites is completed above [Formula: see text] 80 GPa. No convincing evidence of another high-density amorphous state with coordination number larger than six was found within the investigated pressure range. The number of short Ge-Ge and Se-Se "wrong" bonds was found to increase upon pressurization. Experimental XAS results are confirmed by MD simulations, indicating the increase of chemical disorder under high pressure.

EXAFS investigations on the pressure induced local structural changes of GeSe2 glass under different hydrostatic conditions

Pressure-induced transformations in glassy GeSe2 have been studied using the x-ray absorption spectroscopy. Experiments have been carried out at the scanning-energy beamline BM23 (European Synchrotron Radiation Facility) providing a micrometric x-ray focal spot up to pressures of about 45 GPa in a diamond anvil cell. Both Se and Ge K-edge experiments were performed under different hydrostatic conditions identifying the metallization onsets by accurate determinations of the edge shifts. The semiconductor-metal transition was observed to be completed around 20 GPa when neon was used as a pressure transmitting medium (PTM), while this transition was slightly shifted to lower pressures when no PTM was used. Accurate double-edge extended x-ray absorption fine structure (EXAFS) refinements were carried out using advanced data-analysis methods. EXAFS data-analysis confirmed the trend shown by the edge shifts for this disordered material, showing that the transition from tetrahedral to octahedral coordination for Ge sites is not fully achieved at 45 GPa. Results of present high pressure EXAFS experiments have shown the absence of significant neon incorporation into the glass within the pressure range up to 45 GPa.

Structure-terahertz property relationship and femtosecond laser irradiation effects in chalcogenide glasses

We report structure-terahertz (THz) property relationship for various non-oxide chalcogenide glasses including unary (vitreous selenium (Se)), binary (arsenic sulfide (As-S), arsenic selenide (As-Se), and germanium selenide (Ge-Se)), and ternary (germanium arsenic selenide (Ge-As-Se)), systems along with commercially available AMTIR-1, IRG 22, and IRG 24 Ge-As-Se glasses. This comprehensive study is the first of its kind to combine Raman spectroscopy to examine structural units, connectivity, and glass network and terahertz time-domain spectroscopy (THz-TDS) to record the THz refractive index, n(THz), across a broad THz bandwidth. THz-TDS was carried out at Alfred University (AU) and National Institute of Standards and Technology (NIST), ultimately providing confidence in n(THz) values measured at AU. Vitreous Se, <r> = 2.0, record the minimum THz refractive index value of all Se-containing glasses. As-S and As-Se binary glasses have the highest measurable THz refractive index value at <r> = 2.4. Ge-Se binary glasses measure increased THz refractive index as <r> increases, with the maximum at <r> = 2.8. Ternary Ge-As-Se glasses record the maximum THz refractive index value at <r> = 2.5 for Ge10As30Se60. Low-repetition rate femtosecond laser irradiation (≈1 KHz, ≈40 fs, and ≈70 mW) was used to modify As-S and As-Se glass systems, where Raman and THz-TDS were used to observe minimal structural and THz refractive index values changes, respectively. Long-wave infrared (LWIR) (e.g., 10 μm)-THz (e.g., 1.0 THz) refractive index correlation is presented for all binary and ternary studied chalcogenide glasses. Such a correlation is valuable for predicting and designing chalcogenide glasses for integrated optical applications across THz and IR regions.

How arsenic makes amorphous GeSe a robust chalcogenide glass for advanced memory integration

The 3D integration technology in semiconductor fabrication requires a key component, the ovonic threshold switching (OTS) selector, to suppress the current leakage. The As doped amorphous (a-) GeSe glass is a commercialized OTS material in 3D phase-change memory, but the understanding of such a doping mechanism is still inadequate. Here we systematically explore the effect of As doping on the structural, bonding, and dynamics properties of a-GeAsSe using ab initio molecular dynamics simulations. The results reveal that As atoms form strong bonds with both Ge and Se atoms. The distorted octahedral structures and the 5-fold rings linked by atoms are increased. All of these structural features lead to a more disordered configuration. Moreover, As atoms have notably slowed down the atomic mobility, rendering a-GeAsSe a high stability. Our studies offer insightful understanding of As-doping in OTS materials, paving the way for the design and application of advanced selector devices.

Aging-Induced Structural Evolution of a GeSe2 Glass Network: The Role of Homopolar Bonds

The structural evolution of GeSe2 glass during aging is studied using Raman spectroscopy and density relaxation measurements. The Raman spectra indicate volume- and entropy-driven changes in the relative concentrations of the corner-sharing (CS) and edge-sharing (ES) GeSe4 tetrahedra and in the degree of chemical order of the tetrahedral network during aging at 65 °C below the nominal glass transition temperature. The attendant structural changes involve a progressive increase in the CS:ES ratio and in the chemical order that can be expressed in the form of a reaction Ge-Ge + Se-Se → 2 Ge-Se, which shifts to the right, with lowering of fictive temperature. The isothermal relaxation of both the structure and density during aging displays rather similar stretched exponential kinetics with a stretching exponent β ∼0.54 and an average relaxation time of ∼13.5 h. In situ high-temperature Raman spectroscopic measurements indicate that structural relaxation does not affect the anharmonicity of the vibrational potential wells in the energy landscape of GeSe2 glass.

Origin of photoelastic phenomena in Ge-Se network glasses

The elastic properties of a series of Ge-Se glasses are measured during irradiation with sub-band-gap light using a laser-induced transient grating method. The elastic modulus is found to decrease prominently with increasing irradiation intensity. The process is found to be less prominent in glasses of high average coordination $\ensuremath{\langle}r\ensuremath{\rangle}$. Measured kinetics in the millisecond range are found to be too slow for a photoinduced electronic process and instead suggest a thermal origin. Infrared thermography is performed during irradiation to monitor temperature changes during photodarkening, photoexpansion, and photoelastic measurements. It is found that in the conditions of irradiation where photoelasticity is observed, all photostructural changes are directly associated with a change in temperature. comsol modeling of thermal flow through the sample closely reproduces the kinetics of photodarkening. Transient grating measurements as a function of temperature confirm that the change in elasticity during irradiation is essentially a thermally induced process. Currently available experimental evidence indicates that the photoelastic phenomena are not an optoelectronic process but rather the result of laser heating.

Crystal Growth Kinetics in GeS2 Glass and Viscosity of Supercooled Liquid.

The crystal growth kinetics and morphology in germanium disulfide bulk glass and glass surface is described. The structural relaxation taking place below the glass transition is slow and the corresponding volumetric change is negligible. Therefore, it does not affect substantially the crystal growth process. The crystal growth rate of low temperature β-GeS2 and high temperature α-GeS2 polymorphs in the bulk glass is comparable, being slightly decoupled from the shear viscosity below the glass transition. The crystal growth rate of β-GeS2 in an amorphous thin film of the same composition is several orders of magnitude faster than that at the surface of bulk glass. This fast surface crystal growth is strongly decoupled from viscosity. Such behavior resembles the glass-to-crystal fast growth mode observed by several authors in some organic molecular glasses. Taking into account previously reported viscosity and heat capacity data, the crystal growth kinetics of both polymorphs can be quantitatively described by the 2D surface growth model for low and high supercooling. The nonisothermal differential scanning calorimetry experiments are analyzed, providing evidence of a complex nature of the overall crystallization process with apparent activation energy comparable to that obtained from isothermal microscopy measurement of crystal growth in the same temperature range.

Neural Network Quantum Molecular Dynamics, Intermediate Range Order in GeSe2, and Neutron Scattering Experiments.

A remarkable property of certain covalent glasses and their melts is intermediate range order, manifested as the first sharp diffraction peak (FSDP) in neutron-scattering experiments, as was exhaustively investigated by Price, Saboungi, and collaborators. Atomistic simulations thus far have relied on either quantum molecular dynamics (QMD), with systems too small to resolve FSDP, or classical molecular dynamics, without quantum-mechanical accuracy. We investigate prototypical FSDP in GeSe2 glass and melt using neural-network quantum molecular dynamics (NNQMD) based on machine learning, which allows large simulation sizes with validated quantum mechanical accuracy to make quantitative comparisons with neutron data. The system-size dependence of the FSDP height is determined by comparing QMD and NNQMD simulations with experimental data. Partial pair distribution functions, bond-angle distributions, partial and neutron structure factors, and ring-size distributions are presented. Calculated FSDP heights agree quantitatively with neutron scattering data for GeSe2 glass at 10 K and melt at 1100 K.

Extended aging of Ge–Se glasses below the glass transition temperature

Germanium selenide glasses of compositions spanning the whole glass-formation range are aged at room temperature for up to 20 years. A prominent enthalpy relaxation process is observed in all glasses, and its structural origin is analyzed by Raman spectroscopy. The structural relaxation is manifested in the Raman spectra as a decrease in the ratio of edge- to corner-sharing GeSe4/2 tetrahedral units. This structural evolution can be explained in terms of configurational entropy and density changes. Changes in Raman features and enthalpy follow an identical stretched exponential relaxation function characteristic of aging in glasses. The compositional dependence of enthalpy relaxation after 20 years is in agreement with kinetic considerations based on the glass transition temperature of each glass. The relaxation behavior and heat capacity curves are consistent with standard glass relaxation models for all compositions. These results indicate that the non-reversing enthalpy obtained by modulated differential scanning calorimetry (MDSC), which suggests the existence of non-aging glasses, is not a reliable measure of the ability of a glass to relax. Instead, it is suggested that an interpretation of MDSC data in terms of complex heat capacity provides a more complete and reliable assessment of the relaxation properties of glasses.

Ablation of binary As2S3, As2Se3, GeS2, GeSe2 and GeSe3 bulk glasses and thin films with a deep ultraviolet nanosecond laser

Binary (As2S3, As2Se3, GeS2 GeSe2 and GeSe3) bulk glasses and corresponding thin films were prepared and illuminated with deep ultraviolet nanosecond (DUV ns) pulsed laser operating at 213 nm. The illumination of samples led to the reproducible crater's formation. Subsequently, the influence of the pulses number and laser fluence on their creation was studied. The ablation rate and laser-induced ablation threshold (LIAT) were determined based on these experiments. The craters with the help of digital holographic microscopy (DHM), atomic force microscopy (AFM), phase shift imaging mode of AFM, Raman scattering, scanning electron microscopy and energy-dispersive X-ray spectroscopy were characterized. As an application possibility, the formation of the diffraction gratings by laser direct writing is presented and their functionality is demonstrated.

Detailed Investigations on Short- and Intermediate-Range Structures of Ge–Se Glasses near the Stiffness Transition Composition

In order to improve the reliability of short- and intermediate-range atomic structures of GexSe1−x glasses, high quality neutron diffraction data, in both the real and reciprocal spaces, were added...

Homogeneity of melt‐rocked Ge–Se glasses and the effect of impurities

AbstractThe impact of glass synthesis methods on the properties of Ge–Se glasses is investigated. The homogeneity of a GeSe4 glass produced by mechanical convection in a rocking oven for 12 h at 950°C is characterized by Raman spectroscopy and Electron Microprobe analysis. It is found that the melt‐rocked glass is chemically and structurally homogeneous at all length scales investigated. In order to compare the effect of synthesis methods, another glass is produced following a static synthesis for 192 h. Their physical, structural, and dynamic properties are then characterized for comparative analysis. The molar volume and structure of both glasses are found to be identical when subjected to the same thermal history. The structural dynamics of GeSe4 investigated by heat capacity spectroscopy is identical for the static and rocked glass and also compared with that of GeSe9 and GeSe3. Overall, the two synthesis methods do not lead to any difference in measured properties. Finally, the effect of impurities is investigated in three glasses. The presence of water and oxygen impurities up to 30 ppm levels is shown to have no significant effect on physical and structural properties. Hence, the presence of water impurities cannot be attributed to mismatch in physical properties.

Mixed cation Ag2S–Tl2S–GeS2 glasses: macroscopic properties and Raman scattering studies

Mixed cation Ag2S–Tl2S–GeS2 glasses containing 40 and 50 mol% of metal sulfide have been synthesized and analyzed for the first time using thermal analysis, conductivity measurements and Raman spectroscopy. The composition dependences of the ionic conductivity and glass transition temperature Tg showed the presence of classical mixed cation effect with the minimum of both glass transition temperature and room temperature conductivity and the activation energy maximum centered at r = Ag/(Tl + Ag) ≈ 0.2. Raman spectroscopy measurements reveal that the structure of the mixed glasses is not a simple mixture of the end-members, pure thallium (r = 0) and silver (r = 1) thiogermanates. The edge-sharing ES-Ge2S6 dimers and corner-sharing CS-GenS3n+1 (n = 2 or 3) oligomers disappear more quickly than is predicted by the stoichiometry relations. The systematic evolution of the vibrational properties as a function of the silver fraction r also suggests that the both cations are not separated spatially in the glass network but rather located in close proximity to each other.

Distribution of elements in Ge–Se bulk glasses and optical fibers detected by inductively coupled plasma atomic emission spectrometry

The elemental composition of Ge–Se glasses prepared by different methods and the distribution of Ge and Se along the bulk sample length are investigated by inductively coupled plasma atomic emission spectrometry. The estimated uncertainty of Ge and Se content measurement is 0.02–0.05 at.% (P = 0.95). To date, these results are the most accurate for determining the elemental composition of optical Ge-based chalcogenides. The minimum required mass of the analyzed glass samples does not exceed 1 mg. Partial phase separation in the Ge–Se system leads to a significant (±2 at.%) deviation of the chemical composition of Ge–Se glasses along the length of the bulk sample from the specified value. This is the first time that the elemental composition of single-index Ge–Se fibers along the fiber length has been studied. The rod drawing method allows the fabrication of optical fibers with composition deviation along the length of 0.03–0.05 at.%. In the case of drawing by the crucible method, the deviations of the fiber composition can reach 0.16 at.% compared with the initial glass sample.

Mechanical and electrical parameters of a-Ge-Se-Sn glasses

The present work reports the effect of Sn addition on the electrical and mechanical properties of the GeSe2 glass. The measured ultrasonic velocities are used to estimate the elastic moduli and Debye temperature (TD) of the (GeSe2)1−xSnx glasses. The temperature dependence of the electrical parameters and thermo-electrical power of the studied glasses was determined over the temperature range of 300–450 K. The Young's modulus (Y) and bulk modulus (K) as well as the activation energy for the dark electrical conduction (ΔEdc) were correlated with the glass transition temperature (Tg). The observed changes were explained in terms of the distribution of the formed chemical bonds in each glass sample. ΔEdc values decrease while Y and K increase with the increase of Sn content, i.e. the addition of Sn content to the GeSe2 glass enhances both the electrical conductivity and mechanical moduli of Ge-Se-Sn glassy films.

Tl2S–In2S3–GeS2 Glass System as Novel Promising Materials for Photonics

It was established that minimal content of the glass-forming component GeS2 is equal to 30 mol.% (by exploration the set of 23 different alloys with different composition). Correlation between structural properties, thermal parameters (glass transition, crystallization and melting temperatures) and optical absorption spectra along of the titled glasses system has been found. The temperatures, the band gap energy and the characteristic energy of vitreous alloys for the gastric system Tl2S‑In2S3‑GeS2 were investigated experimentally.

2D GeSe2 amorphous monolayer

Abstract In this paper, GeSe2 thin film and glass ingot were prepared in a layered structure. Subsequently, the 2D amorphous monolayers were achieved from layered thin film and layered glass ingot. The thicknesses of monolayers from thin film range from 1.5 nm to 5 nm. And the thickness of monolayer from glass ingot is 7 μm. The fast cooling of material results in the formation of self-assembled monolayers. In the case of thin film, layers are connected with “bridge”. After doping of Ag, the precipitation of nano particles exfoliates the adjacent monolayers which can be further dispersed by etching of Ag particles. In the case of glass ingot, the composition changes at 1 % between adjacent monolayers, according to EDX (energy-dispersive X-ray spectroscopy) spectra. And the glass 2D monolayer can be mechanically peeled off from the glass ingot.