Ternary Ge Research Articles

Far-infrared investigation of ternary Ge–Se–Sb and quaternary Ge–Se–Sb–Te chalcogenide glasses

Chalcogenide glasses are remarkable materials for remote sensors, infrared imaging and infrared fibers due to their transparency in Far-infrared (IR) region. Far-IR absorption spectra of Ge19Se81−xSbx (x=0, 4, 8, 12, 16, 17.2, 20) and Ge19−ySe63.8Sb17.2Tey (y=0, 2, 4, 6, 8, 10) have been obtained in the range of 30–350cm−1. Three possible bond arrangement approaches viz. chain-crossing model (CCM), random-covalent-network model (RCNM) and chemical bond approach (CBA) have been used to discuss the formation of bonds. Results are explained on the basis of GeSe4, GeSe2 and SbSe3 isolated structural units which have appeared in Ge–Se–Sb system while Se6Te2 rings, GeTe4 tetrahedron, GeTe2, GeSe4 and GeSe2 structural units have appeared for Ge–Se–Sb–Te system.

Thermal diffusivity measurements on ternary Ge–Te–Tl glasses using Photo-thermal Deflection method: Effect of thallium addition

Photo-thermal Deflection (PTD) technique is used to investigate the thermal diffusivity (α) of Ge17Te83−xTlx (0≤x≤13) glasses as a function of composition. The thermal diffusivity of these glasses is found to lie in the range 0.020 to 0.048cm2/s, which is consistent with the memory type of electrical switching exhibited by these samples. Further, it is found that α shows an initial increase with Tl addition, followed by a decrease. The observed composition dependence of thermal diffusivity has been understood on the basis that the thallium atoms are incorporated as a covalent species for lower values of x, increasing the network rigidity; however, they enter as ionic species for higher x values, fragmenting the network. The initial increase in α is due to the increasing network rigidity and the subsequent decrease is because of the fragmentation of the network. Also, there is a strong correlation between the composition dependence of switching voltages observed earlier and the variation with composition of electrical resistivity and thermal diffusivity of Ge17Te83−xTlx glasses obtained in the present study.

Ge–Si–O phase separation and Ge nanocrystal growth inGe:SiOx/SiO2 multilayers—a new dc magnetron approach

Ge:SiOx/SiO2 multilayers are fabricated using a new reactive dc magnetron sputtering approach. Theinfluence of the multilayer stoichiometry on the ternary Ge–Si–O phase separation and thesubsequent size-controlled Ge nanocrystal formation is explored by means ofx-ray absorption spectroscopy, x-ray diffraction, electron microscopy and Ramanspectroscopy. The ternary system Ge–Si–O reveals complete Ge–O phase separation at400 °C which does not differ significantly to the binary Ge–O system. Ge nanocrystals of < 5 nm size are generated after subsequent annealing below700 °C. It is shown that Ge oxides contained in the as-deposited multilayers are reduced by asurrounding unsaturated silica matrix. A stoichiometric regime was found where almost noGeO2 is present after annealing. Thus, the Ge nanocrystals become completely embedded ina stoichiometric silica matrix favouring the use for photovoltaic applications.

125Te NMR chemical shifts and tellurium coordination environments in crystals and glasses in the Ge–As–Sb–Te system

The local coordination environments of Te atoms have been investigated in crystalline and glassy binary and ternary tellurides in the system Ge–As–Sb–Te using 125Te solid-state wideline nuclear magnetic resonance (NMR) spectroscopy. The average 125Te NMR chemical shifts in these materials range from 300 to 1050, 90 to 700 and −2000 to −4100ppm for 2, 3 and 6-coordinated environments, respectively. Te atoms are predominantly 2-coordinated in binary Ge–Te, As–Te and ternary Ge–As–Te glasses. The 125Te NMR spectrum of the cubic Ge1Sb2Te4 phase with rock salt structure is consistent with a random distribution of Ge/Sb vacancies in the lattice. Besides the coordination number, the 125Te chemical shifts in these materials are also found to be sensitive to the chemical identity of the nearest neighbors. 125Te NMR spectroscopy shows significant future promise in its application as a technique complementary to diffraction and EXAFS in understanding the short-range structure of amorphous Ge–As–Sb tellurides.

Photo-stability of pulsed laser deposited Ge_xAs_ySe_100-x-y amorphous thin films

Quest for photo-stable amorphous thin films in ternary Ge(x)As(y)Se(100-x-y) chalcogenide system is reported. Studied layers were fabricated using pulsed laser deposition technique. Scanning electron microscope with energy dispersive X-ray analyzer, Raman scattering spectroscopy, transmittance measurements, variable angle spectroscopic ellipsometry, and non-linear imaging technique with phase object inside the 4f imaging system were employed to characterize prepared thin films. Their photo-stability/photo-induced phenomena in as-deposited and relaxed states were also investigated, respectively. In linear regime, we found intrinsically photo-stable relaxed layers within Ge(20)As(20)Se(60) composition. This composition presents also the highest optical damage threshold under non-linear optical conditions.

Structure of GeSe4–In and GeSe5–In glasses

(Ge0.2Se0.8)100 − xInx and (Ge0.17Se0.83)100 − xInx (x = 0, 5, 10, 15 at.%) chalcogenide glasses have been studied with high-energy x-ray diffraction,neutron diffraction and extended x-ray absorption spectroscopy at Ge, Se and In K-edges. Theexperimental data were modelled simultaneously with the reverse Monte Carlo simulation method.GeSe4/2 tetrahedra are shown to be the main structural units in the binary and ternary glassesinvestigated. Indium bonds to the excess Se atoms in the ternary Ge–Se–In glasses. Whilethe majority of In atoms have three Se neighbours, some In atoms may be tetrahedrallycoordinated by Se.

Physical properties of Ge xAs 2xTe 100 − 3x glasses and Raman spectroscopic analysis of their short-range structure

Ternary Ge xAs 2xTe 100 − 3x glasses with 20 ≤ 3x ≤ 70 have been investigated to determine the compositional dependence of select physical properties. Molar volume, viscosity, optical band gap and thermophysical properties display a monotonic and often linear variation with the Te content in these glasses. Such compositional dependence is hypothesized to be due to the progressive replacement of a three-dimensional network of corner-shared Ge and As centered coordination polyhedra by –Te–Te–Te– chains as the Te content increases. This topologic change arises as Ge/As–Ge/As bonds in Te-deficient glasses are gradually replaced by Ge/As–Te bonds and ultimately the Te–Te bonds in Te-excess glasses. The compositional evolution of the Raman spectra of these glasses is shown to be consistent with this structural scenario. Furthermore, detailed analysis of the Raman spectra shows significant violation of chemical order in the form of the presence of Te–Te (Ge/As–Ge/As) bonds in Te-deficient (-excess) glasses. Such behavior in ternary Ge–As telluride glasses is unique in comparison with their sulfide and selenide counterparts.

Far-infrared transmission and bonding arrangement in Ge 10Se 90−xTe x semiconducting glassy alloys

The far-infrared spectra of Ge 10Se 90− x Te x where x = 0, 10, 20, 30, 40, 50 glassy alloys were measured in the wavenumber region 50–650 cm −1 at room temperature. The results were explained in terms of the vibrations of the isolated molecular units. The addition of Te in Ge 10Se 90 has shown the appearance of GeTe 2 and GeTe 4 molecular units and vibrations of Se–Te bond as Se 8− x Te x mixed rings. The assignment of various absorption bands has been made on the basis of absorption spectra of pure Se, binary Ge–Se, Ge–Te, Se–Te and ternary Ge–Se–Te glassy alloys. The far-infrared transmission spectrum has been found to shift a little towards lower wavenumber side with the addition of Te content to Ge 10Se 90. The addition of Te to Ge–Se system replacing Se has found to reduce the Se–Se bonds and Ge–Se bonds and leads to the formation of Se–Te, Ge–Te and Te–Te bonds.

High spin polarization in ternary Ge–Mn–Te compounds based on rocksalt semiconductingGeTe

We study the ternary compoundsGemMnnTep based on rocksalt semiconducting GeTe using a full-potential density-functional method. Form+n = p, we obtaintwo antiferromagnetic semiconductors in which spins are coupled with a superexchange interaction. Lettingm+n<p, we obtain twometallic ferromagnets, Ge3Mn4Te8 and Ge5Mn2Te8. They have full or nearly full spin polarization at the Fermi level. Our study shows thatthe ferromagnetism is favorable because carriers induced by the Ge vacancies make thesuperexchange give way to a Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction. Our results,consistent with experiments, indicate that high spin polarization can be realized in high qualityGe3Mn4Te8 and Ge5Mn2Te8 samples.

Phase stability in Cu–Zn-based ternary alloys with elements of column 14

By adding small amounts of ternary elements Ge, Si or Sn, it is possible to raise the martensitic transformation temperature M S of binary B2 ordered Cu–Zn towards room temperature. Several poly and single crystal ternary alloys have been studied using resistivity and calorimetric measurements, tensile experiments and optical observations. The influence of the composition and thermomechanical pretreatment on the martensitic transformation has been analyzed. It is shown that the increase in the transformation temperature at a constant electron concentration favors competing decomposition mechanisms.

Raman scattering study of GeTe and Ge 2Sb 2Te 5 phase-change materials

Structural details of the amorphous binary GeTe and ternary Ge 2Sb 2Te 5 (GST) phase-change materials are investigated with the aid of Raman scattering. In the case of the a-GeTe, a plethora of Raman bands have been recorded and assigned on the basis of a network structure consisting of corner- and edge-sharing tetrahedra of the type GeTe 4− n Ge n ( n=0, 1, 2, 3, 4). Significant temperature-induced structural changes take place in this material even at temperatures well below the crystallization temperature. These changes tend to organize the local structure, in particular the coordination number of Ge atoms, so as to facilitate the amorphous-to-crystal transformation. The much simpler Raman spectrum of GST, characterized by one vibrational band, is accounted for by the dominance of the Sb 2T 3 component in Raman scattering; reasons about this explanation, as well as for the lack of any Te–Te bonds are briefly described.

Compositional dependence of the optical properties of amorphous semiconducting glass Ge 10As xSe (90−x) thin films

Optical properties of ternary chalcognide amorphous Ge 10As x Se (90− x ) (with 10⩽ x⩽25 at%) thin films prepared by thermal evaporation have been measured in visible and near-infrared spectral region. The straightforward analysis proposed by Swanepoel has been successfully employed, and it has allowed us to determine the average thickness d ¯ , and the refractive index, n, of the films, with high accuracy. The refractive index, n and the average thickness d ¯ has been determined from the upper and lower envelopes of the transmission spectra measured at normal incidence, in the spectral range 400–2500 nm. The absorption coefficient α, and therefore extinction coefficient k, have been determined from the transmission spectra in the strong-absorption region. The dispersion of the refractive index is discussed in terms of the single oscillator Wemple–DiDomenico model, and the optical absorption edge is described using the ‘nondirect transition’ model proposed by Tauc. Likewise, the optical energy gap is derived from Tauc's extrapolation. The relationship between the optical gap and chemical composition in Ge 10As x Se (90− x ) amorphous system is discussed in terms of the average heat of atomization H s and average coordination number N c. Finally, the chemical bond approach has been also applied successfully to interpret the decrease of the glass optical gap with increasing As content.

Structural changes in amorphous chalcogenide semiconductors under high pressure: a Raman study

AbstractThe Raman spectra of binary As–S and ternary Ge–As–S semiconducting chalcogenide glasses have been studied under variable hydrostatic pressure up to 7.0 GPa. Two As–S glasses were investigated, the first at the stoichiometric composition As2S3 (with critical mean coordination number value Z = 2.4) and the other S‐rich, non‐stoichiometric one belonging to the floppy network regime (AsS4, Z = 2.2), while the ternary Ge–As–S glass was on the rigid network side (Ge25As10S65, Z = 2.6). Reversible pressure‐induced effects have been observed in the floppy AsS4 glass manifested by the amorphization of its crystalline sulphur domains. In contrast, the pressure‐induced appearance of homopolar Ge–Ge bonds and the formation of “ethanol‐like” S3Ge–GeS3 units in the rigid ternary Ge25As10S65 glass are irreversible, after pressure relief. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

PAL spectroscopy as experimental probe for extended free-volume defects in inorganic glasses and ceramics

Extended free-volume defects trapping positrons are studied in inorganic glasses and functional ceramics using positron annihilation lifetime spectroscopy. Obtained results are treated in terms of general macroscopic approach grounded on physical–chemical properties of the tested materials which depend on the value of free volume content. At the example of chalcogenide glasses of ternary Ge–Sb–S system and spinel-type mixed transition-metal manganite Cu 0.4Co 0.4Ni 0.4Mn 1.8O 4 and magnesium aluminate MgAl 2O 4 ceramics, it is shown that strict correlation exists between numerical values of free volumes of potential positron traps and lifetime parameters determined within two-state positron trapping model.

Radiation-induced bond switching in mixed Ge–As sulphide glasses

A mechanism for γ-ray-induced changes in the optical properties of ternary Ge–As sulphide glasses is analysed at the microstructural level. It is shown, using IR FFT spectroscopy, that these changes are associated with chemical bond switching accompanied by coordination topological defect formation.

Influence of the substrate temperature on the structure of Ge containing thin films produced by ArF laser induced chemical vapour deposition

Ge, SiGe and SiGeC films were grown on Si(1 0 0) and Corning glass (7059) substrates by ArF-excimer laser induced chemical vapour deposition in parallel configuration. Different substrates temperatures ranging from 180 to 400 °C, for a fixed reactant gas composition, were used at constant total pressure and laser power. The analysis of the films showed the existence of a relationship between the substrate temperature and the deposition rate as well as to the film properties. A comparison among the pure, binary and ternary Ge containing system was performed to study the influence of the presence of different gases in the reactant mixture. Structural properties of the deposited films were investigated by Raman and Fourier transform infrared spectroscopy. Their surface morphology was evaluated by scanning electron microscopy and atomic force microscopy (AFM). X-ray photoelectron spectroscopy (XPS) revealed the composition of the alloys and X-ray diffraction experiments demonstrated the polycrystallinity of some pure Ge films.

Electrical properties and microstructure of ternary Ge∕Ti∕Al ohmic contacts to p-type 4H–SiC

The high-power SiC devices require ohmic contact materials, which are prepared by annealing at temperatures lower than 800°C. Recently, we demonstrated in our previous paper [J. Appl. Phys. 95, 2187 (2004)] that an addition of a small amount of Ge to the conventional binary Ti∕Al contacts reduced the ohmic contact formation temperature by about 500°C, and this ternary contacts yielded a specific contact resistance of approximately 1×10−4Ωcm2 after annealing at a temperature as low as 600°C. In this paper, the electrical properties and the microstructures of the Ge∕Ti∕Al contacts (where a slash “/” indicates the deposition sequence) were investigated by current-voltage measurements and transmission electron microscopy observations, respectively, in order to understand the ohmic contact formation mechanism. Ti3SiC2 compound layers (which were previously observed at the metal/SiC interface in the Ti∕Al ohmic contacts after annealing at temperatures higher than 1000°C) were observed to grow epitaxially on the SiC surface after annealing at temperatures as low as 600°C. The Ti3SiC2 layers were believed to act as a p-type intermediate semiconductor layer, which played a key role to reduce the Schottky barrier height at the contacting metal/SiC interface. Further reduction of the contact resistances of the Ge∕Ti∕Al contacts would be achieved by increasing the coverage of the Ti3SiC2 layers on the SiC surface.

Nonlinear optical properties of chalcogenide glasses: comparison between Mach–Zehnder interferometry and Z-scan techniques

To explore the potentialities of chalcogenide glasses for ultrafast optical switching, the nonlinear refractive indices of different compositions are measured. Several binary glasses as well as ternary ones have been characterized. Nonlinear measurements has been performed through a pump/probe experiment using a Mach–Zehnder interferometer coupled to a CCD camera. Nonlinear refractive index as high as 12×10 −18 m 2/W have been obtained in the ternary (Ge–Se–As) system. A comparison with the nonlinear coefficients obtained with the Z-scan technique is performed. Results show that, although the order of magnitude is the same, a systematic discrepancy exists, in particular for high nonlinear absorption for which the relative error reaches up to 50%. We show that this is a consequence of the use of simplified formulas derived in the Z-scan technique. Indeed, a detailed analysis demonstrates that both techniques perfectly agree when a higher-order development is used for the determination of the nonlinear coefficient from the Z-scan technique.

Sharp Rigid to Floppy Phase Transition Induced by Dangling Ends in a Network Glass

Laboratoire de Physique Theorique des Liquides, Universite Pierre et Marie Curie, Boite 121, 4 Place Jussieu,75252 Paris, Cedex 05, France(Received 29 March 2001; published 16 October 2001)The count of Lagrangian bonding constraints in ternary Ge S I glasses isestablished from the molecular structure using Raman scattering and Þrst-principles cluster calculations.The results show that decreases to 3 as y increases close to , where a sharply deÞnedglobal minimum in the nonreversing heat sow, near , is observed in scanning calorimetry.Here we have a rigidity transition induced by I dangling ends, with its sharpness resulting from theabsence of self-organization in the random network.

Study of the Ternary System Germanium—Antimony—Tin: Experimental Phase Diagram.

Abstract The phase diagram of the ternary system Ge–Sb–Sn was established by X-ray powder diffraction and differential scanning calorimetry. No ternary compound was found. Two vertical sections were studied in order to follow the reaction path. Four ternary reactions were characterised: three transition peritectic (U-type) reactions and one eutectoid (E-type) reaction. Moreover, from all equilibrium temperatures, a description of liquidus surface in the whole composition range is proposed.