Amorphous Ge‐Sb‐Se thin films fabricated by co‐sputtering: Properties and photosensitivity

Amorphous Ge–Sb–Se thin films were fabricated by a rf‐magnetron co‐sputtering technique employing the following cathodes: GeSe₂, Sb₂Se₃, and Ge₂₈Sb₁₂Se₆₀. The influence of the composition, determined by energy‐dispersive X‐ray spectroscopy, on the optical properties was studied. Optical properties were analyzed based on variable angle spectroscopic ellipsometry and UV‐Vis‐NIR spectrophotometry. The results show that the optical bandgap range 1.35‐2.08 eV with corresponding refractive index ranging from 3.33 to 2.36 can be reliably covered. Furthermore, morphological and topographical properties of selenide‐sputtered films studied by scanning electron microscopy and atomic force microscopy showed a good quality of fabricated films. In addition, structure of the films was controlled using Raman scattering spectroscopy. Finally, irreversible photoinduced changes by means of change in optical bandgap energy and refractive index of co‐sputtered films were studied revealing the photobleaching effect in Ge‐rich films when irradiated by near‐bandgap light under Ar atmosphere. The photobleaching effect tends to decrease with increasing antimony content.     

X‐ray photoelectron spectroscopy analysis of Ge–Sb–Se pulsed laser deposited thin films

Pulsed laser deposition was used to prepare amorphous thin films from (GeSe₂)_100?x(Sb₂Se₃)_x system (x = 0, 5, 10, 20, 30, 40, 50, and 60). From a wide variety of chalcogenide glass‐forming systems, Ge–Sb–Se one, especially in thin films form, already proved to offer a great potential for photonic devices such as chemical sensors. This system has a large glass‐forming region which gives the possibility to adjust the chemical composition of the glasses according to required physical characteristics. The chemical composition of fabricated thin films was analyzed via X‐ray photoelectron spectroscopy (XPS) and compared to energy dispersive spectroscopy (EDS) data. The results of both techniques agree well: a small deficiency in chalcogen element and an excess of antimony was found. The structure of as‐deposited thin films has been investigated by XPS. The presence of the two main structural units, [GeSe₄] and [SbSe₃] proposed by Raman scattering spectroscopy data analysis, was confirmed by XPS. Moreover, XPS core level spectra analysis revealed the presence of M–M bonds (M = Ge, Sb) in (Ge,Sb)–Ge–(Se)₃ and (Ge,Sb)–Sb–(Se)₂ entities that could correspond to Ge‐based tetrahedra and Sb‐based pyramids where one of its Se atoms at corners is substituted by Ge or Sb ones. The content of depicted M–M bonds tends to increase with introduction of antimony in the amorphous network of as‐deposited thin films from x = 0 to x = 40 and then it decreases. XPS analysis of as‐deposited thin films shows also the presence of the (Ge,Sb)–Se–(Ge,Sb) and Se–Se–(Ge,Sb) entities.     

Formation of Heterojunction Networks in the Photoelectrical Glass–Ceramics: A Thermal Analysis

The photoelectrical glass–ceramics GeSe₂–Sb₂Se₃–CuI which contain self‐organized heterojunction networks is a novel and promising photovoltaic material. Here, a series of these glass–ceramics with gradually changed GeSe₂/Sb₂Se₃ ratios are studied. The composition dependence of the crystallization behavior is analyzed by differential scanning calorimetry and compared with the composition dependence of the photoelectrical properties. It is revealed that the glass–ceramics with evident photoelectrical response show two common features in differential scanning calorimetry curves: an overlapping crystallization peak attributed to the coprecipitation of Cu₂GeSe₃ and Sb₂Se₃, and peak profiles showing the characteristics of direct impingement growth. Based on these results, it is concluded that the formation of the heterojunction networks in the photoelectrical glass–ceramics is ascribed to the kinetically allowed eutectoid crystallization of Cu₂GeSe₃ and Sb₂Se₃.     

Structure and physical properties of Ge15Sb20Se65‐xSx glasses

We explored the structure and physical properties of Ge₁₅Sb₂₀Se_65‐xS_x (with x = 0, 16.25, 32.5, 48.75, and 65) glasses in order to screen the best compositions for the applications in photonics, since the laser damage thresholds in Se‐based glasses are too low although their optical nonlinearities are high. We found that, linear and nonlinear refractive index of the glasses decreased, but glass transition temperature T_g, optical bandgap E_g and the laser damage threshold increased with increasing S content. We further employed Raman scattering and high‐resolution X‐ray photoelectron spectra to probe the structure of the glasses. Through the analysis of the evolution of the different structural units in the glasses, it was concluded that, the heteropolar bonds (Ge–Se/S, Sb–Se/S) were dominated in these glasses. With the increase in chalcogen Se/S ratio, the number of the Se‐related chemical bonds (Ge–Se, Sb–Se and Se–Se) increased and that of S‐related chemical bond (Ge–S, Sb–S and S–S) decreased gradually, and Ge was prior to bond with S rather than Se. The elemental substitution thus had negligible effect on the glass structure. The change of the physical properties was mainly due to the difference of the strength of the chemical bonds between S–Ge(Sb) and Se–Ge(Sb).     

Glass Formation and Ionic Conduction Behavior in GeSe2–Ga2Se3–NaI Chalcogenide System

Series of glassy and glass‐ceramic samples in the GeSe₂–Ga₂Se₃–NaI system is prepared by melt‐quenching technique and the glass‐forming region is well‐defined by XRD investigations. Na‐ion conduction behavior is systemically studied by impedance measurements. For the glasses in the series (100?2x)GeSe₂–xGa₂Se₃–xNaI, ionic conductivities increased with increasing x, whereas the attributed activation energy of ion conduction decreases. The enhanced mechanism is discussed by employing Raman spectra. In addition, the effect of the crystal phases NaI and Ga₂Se₃ on the ionic conduction behavior in the (70?x)GeSe₂–xGa₂Se₃–30NaI samples is discussed. Although it shows that the poorly conducting crystallites of NaI and Ga₂Se₃ have a negative effect on the ionic conductivities in this series, the highest ionic conductivity of 1.65 × 10^?6 S/cm is obtained in the 45GeSe₂–25Ga₂Se₃–30NaI glass. Finally, this study also demonstrates a possible way to search appropriate Na‐ion solid electrolytes for all‐solid‐state batteries.     

Low gallium-content,dysprosium III-doped,Ge–As–Ga–Se chalcogenide glasses for active mid-infrared fiber optics

A systematic investigation is presented, for the first time, of a 1000 ppmw (parts per million, by weight) Dy³⁺-doped Ge–As–Ga–Se chalcogenide glass series, with a fixed low Ga content of 1 atomic% (at. %), suitable for active mid-infrared fiber optics. Seven glasses constitute the series, which have increasing average coordination number from 2.49 to 2.61, in steps of 0.02, with the GeSe₂, As₂Se₃, and Ga₂Se₃ stoichiometries kept. Glass formation is confirmed using X-ray diffraction and differential scanning calorimetry. Fourier transform infrared spectroscopy is reported for the series. Parallel plate viscometry enables prediction of fiber-drawing temperatures and, with differential thermal analysis, determines the potential for fiber fabrication. X-ray diffraction of samples after parallel-plate viscometry shows that Ge₂₅As₉Ga₁Se₆₅ (at. %) alone, in the glass-series, devitrifies to form the single-crystalline phase: monoclinic-GeSe₂; scanning electron microscope imaging suggests that this phase is both surface and bulk grown. Overall, the recommended host glass at. % compositions for doping with rare-earth ions and drawing to active mid-infrared fiber are: Ge_17.5As₁₈Ga₁Se_63.5, Ge₁₅As₂₁Ga₁Se₆₃, and Ge_12.5As₂₄Ga₁Se_62.5.     

High-performance acousto-optic modulator based on environmentally favorable Ge20Sb15Se65 chalcogenide glass

Acousto-optic (AO) properties of an environmentally friendly Ge₂₀Sb₁₅Se₆₅ chalcogenide glass were investigated, and the results show that Ge₂₀Sb₁₅Se₆₅ glass was a potential material for manufacturing AO modulator (AOM) because its composition possesses excellent performance of high optical quality and transmission in the infrared region spectral, non-toxic, high glass transition temperature, strong mechanical strength, easy to fabricate in large bulk, and isotropic homogeneity. Particularly, its outstanding AO figure of merit (M₂ = 407 × 10⁻¹⁵ s³/kg) was approximately 270 times that of fused quartz glass, making it attractive for AO device designs. Herein, the construction of the AOM based on Ge₂₀Sb₁₅Se₆₅ glass as AO material was performed, and we obtained a high diffraction efficiency of 73.4% at a high acoustic frequency of 160 MHz and an extremely low radio-frequency (RF) power of 0.25 W when the laser beam at 1550 nm was controlled. To our best knowledge, the results of initial tests on the AOM prepared from Ge–Sb–Se chalcogenide glass were first reported. Such an AOM design enriches the family of AO devices and exploits the route for the practical application of chalcogenide glass.     

First Identification of Rare‐Earth Oxide Nucleation in Chalcogenide Glasses and Implications for Fabrication of Mid‐Infrared Active Fibers

Gallium (Ga) helps solubilize rare‐earth ions in chalcogenide glasses, but has been found to form the dominant crystallizing selenide phase in bulk glass in our previous work. Here, the crystallization behavior is compared of as‐annealed 0–3000 ppmw Dy³⁺‐doped Ge–As–Ga–Se glasses with different Ga levels: Ge_16.5As_(19?x)Ga_xSe_64.5 (at.%), for x = 3 and 10, named Ga₃ and Ga₁₀ glass series, respectively. X‐ray diffraction and high‐resolution transmission electron microscopy are employed to examine crystals in the bulk of the as‐prepared glasses, and the crystalline phase is proved to be the same: Ge‐modified, face centered cubic α‐Ga₂Se₃. Light scattering of polished glass samples is monitored using Fourier transform spectroscopy. When Ga is decreased from 10 to 3 at.%, the bulk crystallization is dramatically reduced and the optical scattering loss decreases. Surface defects, with a rough topology observed for both series of as‐prepared chalcogenide glasses, are demonstrated to comprise Dy, Si, and [O]. For the first time, evidence for the proposed nucleation agent Dy₂O₃ is found inside the bulk of as‐prepared glass. This is an important result because rare‐earth ions bound in a high phonon–energy oxide local environment are, as a consequence, inactive mid‐infrared fluorophores because they undergo preferential nonradiative decay of excited states.     

Controllable Formation of the Crystalline Phases in Ge–Ga–S Chalcogenide Glass‐Ceramics

We prepared chemically stoichiometric, S‐poor and S‐rich Ge–Ga–S glasses and annealed them at a temperature that was 20°C higher than its respective glass transition temperature. We aimed at tuning the formation of the different crystals in chalcogenide glass‐ceramics. Through systematic characterization of the structure using X‐ray diffraction and Raman scattering spectra, we found that, GeS₂ and GeS crystals only can be created in S‐rich and S‐poor glass‐ceramics, respectively, while all GeS, Ga₂S₃, and GeS₂ crystals exist in chemically stoichiometric glass‐ceramics. Moreover, we demonstrated the homogeneous distribution of the crystals can be formed in the S‐rich glass‐ceramics from the surface to the interior via composition designing. The present approach blazes a new path to control the growth of the different crystals in chalcogenide glass‐ceramics.     

Laser Desorption Ionization Time‐of‐Flight Mass Spectrometry of Glasses and Amorphous Films from Ge–As–Se System

Laser Desorption Ionization Time‐of‐Flight Mass Spectrometry was exploited for the characterization of Ge–As–Se chalcogenide glasses and corresponding thin films fabricated using pulsed laser deposition. Main achievement of the paper is the determination of laser generated clusters’ stoichiometry. The clusters observed were As_b⁺ (b = 1–3), Se₂^?, binary As_bSe⁺ (b = 1–3), As_bSe_c^? (b = 1–3, c = 1–4), Ge₂Se_c^? (c = 2–3), As₃Se₂⁺, Ge₂As_b^? (b = 2–3), Ge₃As_b^? (b = 1–2), Ge₃Se₄^?, As₅Se_c^? (c = 4–5), GeAsSe₄^?, Ge_aAsSe₅^? (a = 1–4), GeAs₂Se₃^?, GeAs₃Se₂^?, Ge₂As₂Se₂^?, Ge₂AsSe_c^? (c = 6–7), and GeAs₃Se_c^? (c = 5–6) (in positive as well as in negative ion mode). The stoichiometries of identified species are compared with the structural units of the glasses/thin films revealed via Raman scattering spectra analysis. Some species are suggested to be fragments of bulk glass as well as thin films. Described method is useful also for the evaluation of the contamination of chalcogenide glasses or their thin films.     

Correlating Structure with Threshold Behavior of Chalcogenide Glasses Within Ge–Sn–Se Ternary System

A systematic investigation of the optical and structural properties of chalcogenide glasses in Ge–Sn–Se ternary system is presented. We have found a threshold behavior of optical property, namely, existence of transitional composition of the Ge–Sn–Se glasses, with progressive replacement of Se by Sn. Calculation of mean coordination number indicates that the transition‐like feature of optical property is associated with the evolution of chemical ordering of the Ge–Sn–Se network. Analysis of Raman spectra of the glasses explains that the interaction between Se–Se bonds, Sn(Se_1/2)₄ tetrahedra, and Sn–Sn homopolar bonds is the origination of such optical phenomenon.     

Signature of rigidity percolation effect in dielectric behavior of germanium containing multi-component chalcogenide glasses (ChGs)

To develop new chalcogenide glasses (ChGs) as dielectric materials having a high dielectric constant and low dielectric loss, some quaternary glasses have been prepared from a novel third-generation Se–Te–Sn-Ge (STSG) system. This study reveals the effect of Ge addition on the dielectric relaxation and thermally activated a.c. conduction in a ternary ChG of Se–Te–Sn (STS) system. The compositional variation of the various dielectric and electrical parameters in the present STSG chalcogens rich non-oxide glasses Se_78-yGe_yTe₂₀Sn₂ (0 ≤ y ≤ 6) has been investigated. The results show that Ge plays a potential role in improving the dielectric properties of the parent STS glass.The dielectric relaxation and thermally assisted a.c. conduction have been investigated by examining the frequency/temperature dependence of dielectric constant/loss. The absence of the dielectric relaxation for the higher concentration of Ge indicates that the relationship of microstructure and dielectric properties can be explained in terms of the stiffness transition followed by the self-organization of the corner sharing and the edge-sharing arrangements of GeSe₄ phase.     

Physicochemical and optical properties of glasses in the Ga<Subscript>4</Subscript>Ge<Subscript>21</Subscript>Se<Subscript>50</Subscript>-Sb<Subscript>2</Subscript>Se<Subscript>3</Subscript> system

This paper reports on the results of an investigation into the concentration behavior of the glass-forming ability, heat resistance, glass transition temperature, density, refractive index, transparent spectral region, and impurity optical absorption of glasses in the Ga₄Ge₂₁Se₅₀-Sb₂Se₃ system. The data obtained indicate that glasses in the Ga₄Ge₂₁Se₅₀-Sb₂Se₃ system with a high Sb₂Se₃ content are of interest as materials for use in fiber optics.     

In‐Situ Raman Spectroscopy Study of Photoinduced Structural Changes in Ge‐rich Chalcogenide Films

Very few studies have been directed at the compositional dependence of the intrinsic photostability of the Ge_xSe_1?x binary ChG films especially for the Ge‐rich films with the mean coordination number (MCN) larger than 2.67. Here, by measuring the in‐situ transmission changes, it shows that the photosensitivity (e.g., photobleaching, PB) of the Ge‐rich films (as compared to the GeSe₂ film) is attenuated, in fact almost completely eliminated in the film with the largest MCN. A straightforward technique, in‐situ Raman spectroscopy, is used to record the time‐resolved intrinsic structural changes during the irradiation of the films. The result indicates a transition from PB towards photostability occurs at the critical composition of GeSe₂ corresponding to the structural phase transition. The stressed rigid structures of the Ge‐rich films inhibit any significant photo‐structural changes.     

Study on crystallization behaviors of As–Se–Bi chalcogenide glasses

The crystallization behaviors of As–Se–Bi chalcogenide glasses were investigated by differential scanning calorimetry (DSC) and X‐ray diffraction (XRD). Three models were used to study the glass transition behavior and the activation energy. Results showed thermal stability of glass against crystallization decreased with Bi addition in As–Se–Bi system. The mechanism of crystal growth in glasses was also studied by the Avrami exponent n. For B0, B2.5, and B5, n values are 3.12, 1.59, and 2.21 (low temperature) and 4.61 (high temperature), respectively. The thermal stability of glass is in good agreement with glass network structure. It was found that glass network structures closely associated with the Bi content and As/Se ratio were studied by X‐ray diffraction and Raman spectroscopy. And the different ratios lead to the change in Bi₂Se₃ crystalline orientation.     

Dy3+‐Doped Selenide Chalcogenide Glasses: Influence of Dy3+ Dopant‐Additive and Containment

This work reports on process‐induced impurities in rare‐earth ion: Dy³⁺‐doped selenide chalcogenide glasses, which are significant materials for active photonic devices in the mid‐infrared region. In particular, the effect of contamination from the silica glass ampoule containment used in chalcogenide glass synthesis is studied. Heat‐treating Dy‐foil‐only, and DyCl₃‐only, separately, within evacuated silica glass ampoules gives direct evidence of silica ampoule corrosion by the rare‐earth additives. The presence of [Ga₂Se₃] associated with [Dy] on the silica glass ampoule that has been contact with the chalcogenide glass during glass melting, is reported for the first time. Studies of 0–3000 ppmw Dy³⁺‐doped Ge_16.5As₉Ga₁₀Se_64.5 glasses show that Dy‐foil is better than DyCl₃ as the Dy³⁺ additive in Ge‐As‐Ga‐Se glass in aspects of avoiding bulk crystallization, improving glass surface quality and lowering optical loss. However, some limited Dy/Si/O related contamination is observed on the surfaces of Dy‐foil‐doped chalcogenide glasses, as found for DyCl₃‐doped chalcogenide glasses, reported in our previous work. The surface contamination indicates the production of Dy₂O₃ and/or [≡Si‐O‐Dy=]‐containing particles during chalcogenide glass melting, which are potential light‐scattering centers in chalcogenide bulk glass and heterogeneous nucleation agents for α‐Ga₂Se₃ crystals.     

High extinction-ratio microstructure fiber based on chalcogenide glasses

Extinction ratio (ER) is one of the important parameters to characterize the polarization-maintaining (PM) performance of the fiber. In this paper, we report the preparation and properties of a novel chalcogenide microstructure fiber with a high ER. We fabricate a preform using a peeled-off extrusion method. The core and cladding material of the fiber are Ge₉As₂₃Se₆₈ and Ge₁₀As₂₂Se₆₈. The preform was drawn into a fiber with an average ER of −17.08 dB. The loss of the fiber is less than 2 dB over 5.20–8.55 μm, and the minimum loss of the fiber is 0.57 dB/m at 6.2 μm. Moreover, a flat mid-infrared supercontinuum spectrum spanning from 1.53 to 12.50 μm is generated by pumping an 18-cm-long PM fiber for the first time.     

1.8–13 μm supercontinuum generation by pumping at normal dispersion regime of As–Se–Te glass fiber

Mid-infrared (MIR) band supercontinuum (SC) light source has highly important application prospects in aerospace, biomedicine, MIR sensing, and pollutant monitoring. As–Se–Te glass has high nonlinear refractive index, wide MIR transmission range and weak crystallization ability. As₄₀Se₄₀Te₂₀ glass fiber is suitable for producing wide MIR–SC spectrum. In this study, purified As₄₀Se₄₀Te₂₀ glass was prepared and unclad and step-index fibers were drawn. An unclad As₄₀Se₄₀Te₂₀ glass fiber with minimum loss of 1.7 dB/m at 8.8 μm was obtained. By pumping the unclad fiber in the normal dispersion region at 5 μm, we recorded the broadest SC generation spectrum, which covered 1.8–13 μm with a 30 dB spectral flatness, from a fiber with 15 cm length. Besides, As₄₀Se₄₀Te₂₀/As₄₀Se₄₂Te₁₈ step-index fiber with minimum loss of 5.6 dB/m at 5 μm was drawn from isolation extruded preform. The step-index fiber was pumped in the normal dispersion region at 5 μm, and the SC spectrum, covering 2.1–11.2 μm with a 40 dB spectral flatness, was recorded from a fiber with 15 cm length. The SC spectrum, which was achieved by pumping the As₄₀Se₄₀Te₂₀ fiber, covered almost all the transparent range of material.     

Magnetic Ni doping induced high power factor of Cu2GeSe3-based bulk materials

Cu₂GeSe₃ is an eco-friendly material, but pristine Cu₂GeSe₃ has poor thermoelectric properties. Here, the effects of magnetic Ni ion with unpaired 3d electrons on the electrical and thermal transport properties of Cu₂GeSe₃ are reported. Density functional theory (DFT) calculations indicate that the unpaired Ni 3d states cause the hybridization of Ni 3d orbitals with Se 4p orbitals near the Fermi level, giving rise to an increase in density of states (DOS). Combined with the significantly increased carrier concentration, a power factor (S²σ) value of ～8.0 μWcm^?1 K^?2 at 723 K is achieved in Cu₂Ge_0.8Ni_0.2Se₃ sample, seeming to be the highest compared with the other Cu₂GeSe₃ systems. Meanwhile, the substitution of Ni for Ge causes the obvious local distortions in Cu₂GeSe₃ lattice, which yields the large strain fluctuations to suppress the lattice thermal conductivity. Consequently, a peak ZT value of ～0.38 at 723 K is obtained in Cu₂Ge_0.9Ni_0.1Se₃ sample.