GeO2 Oxide Research Articles

Structural transformation and anomalous diffusion in network forming liquid GeO2

In this study, we simulated the structural transformation and self-diffusion mechanism in liquid GeO2 oxide system. Under compression, structure of liquid GeO2 model tends to transform gradually from low-density phase to high-density phase. Concentration of basic structural units can be determined via density of material model. The average Ge–O bond distance in GeO4 tetrahedra is smaller than the ones in GeO5 pentahedra and GeO6 octahedra. Each GeOx polyhedron always exists a Ge–O bond with the longest length (the weakest bond). The diffusion mechanism in liquid GeO2 oxide system is via breaking the weakest bonds that accompany the change local coordination environment of Ge cations. The longest Ge–O bond in a GeO5 pentahedron is very weak in comparison to the one in other polyhedra. The diffusivity is significantly dependent on the number of GeO5 pentahedra. The increase of GeO5 under compression is the origin of anomalous diffusion in liquid GeO2 oxide. The increase of average Ge–O bond distance under compression is also clarified in this work.

Crystal structure and thermodynamic properties of germanate CuEu-=SUB=-2-=/SUB=-Ge-=SUB=-2-=/SUB=-O-=SUB=-8-=/SUB=-

Copper-europium germanate CuEu2Ge2O8 was obtained from the initial CuO, Eu2O3 and GeO2 oxides using solid-phase synthesis by annealing in air in the temperature range of 1223-1273 K. Its crystal structure was determined (space group Cm). The influence of temperature on high-temperature heat capacity of the synthesized germanate was studied by the differential scanning calorimetry method. It was found that the dependence of heat capacity on temperature has an extreme value related to a phase transition. The thermodynamic properties were calculated based on the experimental data about heat capacity. Keywords: copper-europium germanate, solid-phase synthesis, crystal structure, thermodynamic properties.

Structure and Thermodynamic Properties of the SmGaGe2O7 Oxide

The SmGaGe2O7 oxide material has been obtained from initial Sm2O3, Ga2O3, and GeO2 oxides by solid-phase synthesis with annealing in air in the temperature range of 1273–1473 K. The structure of the investigated germanate (sp. gr. P21/c, a = 7.18610(9) A, b = 6.57935(8) A, and c = 12.7932(2) A) has been established by X-ray diffraction and the high-temperature heat capacity has been determined by differential scanning calorimetry. Using the experimental data on Cp = f(T), the thermodynamic properties of the compound have been calculated.

Структура и термодинамические свойства SmGaGe-=SUB=-2-=/SUB=-O-=SUB=-7-=/SUB=-

SmGaGe2O7 has been prepared by solid-phase synthesis in air at temperatures from 1273 to 1473 K using the Sm2O3, Ga2O3, and GeO2 oxides as starting materials. The structure of the studied germanate was determined by X-ray diffraction (space group P2_1 / c; a = 7.18610(9) Angstrem, b = 6.57935(8) Angstrem, c = 12.7932(2) Angstrem). Its high-temperature heat capacity has been measured by differential scanning calorimetry. The obtained experimental dependence C_p = f (T) has been used to evaluate the thermodynamic properties of the compound.

Effect of introduction of TiO2 and GeO2 oxides on thermal stability and 2 μm luminescence properties of tellurite glasses

Abstract In this paper, Tm3+ doped pure tellurite glass, TiO2 modified tellurite glass and TiO2/GeO2 co-modified tellurite glasses were prepared. The effects of the introduction of TiO2 and GeO2 oxides on the thermal, structural, optical properties of tellurite glasses were compared and analyzed intensively. Besides, the Judd-Ofelt intensity parameters and absorption and emission cross sections were calculated. DTA curves indicated the thermal stability of pure tellurite glass enhance obviously by GeO2 modification. The introduction of TiO2 and GeO2 oxides in tellurite glasses arise a series of variation on the absorbance, luminescence peak position and fluorescence intensity which have been explained and analyzed in detail. Based on the analysis, the addition of TiO2 in tellurite glass contributes to the improvement of 2 μm fluorescence performance, and the introduction of GeO2 has great advantages in enhancing the thermal stability of glass.

Solid-state synthesis and characterization of ferromagnetic Mn5Ge3 nanoclusters in GeO/Mn thin films

Mn5Ge3 films are promising materials for spintronic applications due to their high spin polarization and a Curie temperature above room temperature. However, non-magnetic elements such as oxygen, carbon and nitrogen may unpredictably change the structural and magnetic properties of Mn5Ge3 films. Here, we use the solid-state reaction between Mn and GeO thin films to describe the synthesis and the structural and magnetic characterization of Mn5Ge3(Mn5Ge3Oy)-GeO2(GeOx) nanocomposite materials. Our results show that the synthesis of these nanocomposites starts at 180°С when the GeO decomposes into elemental germanium and oxygen and the resulting Ge atoms immediately migrate into the Mn layer to form ferromagnetic Mn5Ge3 nanoclusters. At the same time the oxygen atoms take part in the synthesis of GeOx and GeO2 oxides and also migrate into the Mn5Ge3 lattice to form Mn5Ge3Oy Nowotny nanoclusters. Magnetic analysis assumes the general nature of the Curie temperature increase in carbon-doped Mn5Ge3Cx and Mn5Ge3Oy films. Our findings prove that not only carbon, but oxygen may contribute to the increase of the saturation magnetization and Curie temperature of Mn5Ge3-based nanostructures.

Mapping Strain and Composition Effects on Gesn Band Structure Using Spectroscopic Ellipsometry

One of the most interesting research areas in silicon photonics has been the development of silicon-compatible electro-optical devices including detectors, modulators, and light sources, to name a few. IN this regard, the binary alloy Ge1-xSn x has been of particular importance due its bandgap directness in contrast to silicon and germanium.[1-2] As a matter of fact, great efforts have been expended in recent years towards the development of the epitaxial growth of high-quality GeSn crystals on silicon platform and their introduction in design and fabrication of optoelectronic devices.[3] This interest has been nurtured by the ability to manipulate the GeSn band structure by controlling Sn composition and strain. These two degrees of freedom provide flexibility to tune the optoelectronic properties relevant to a variety of devices. For instance, GeSn is attractive material system for photodetectors with absorption edge extending over a broad wavelength range from the short wavelength infrared (SWIR, 1.6-2 µm) to the mid-infrared (MIR, 2-5 µm). In this perspective, this work reports detailed investigations of the influence of both strain and composition on the band structure above 1 eV of GeSn ternary alloys through a spectroscopic ellipsometry study. Understanding the individual influence of each parameter is highly critical to establish and optimize the properties of GeSn device layers. GeSn thin films investigated in this work were grown using a low-pressure Chemical Vapor Deposition (LP-CVD) at different Sn compositions in the 7-18 at.% range.[4] A graded growth process on Ge-virtual substrates was used. Figure A shows a typical example of the investigated samples. The figure exhibits a schematic representation where the bottom layer (BL- 6.3% of Sn) and the top layer (TL- 12.5% of Sn) have different Sn composition. Furthermore, High-Resolution X-Ray Diffraction (HR-XRD) was used to characterize the compressive strain present in each layer. In the sample shown in Figure A, the strain was found to be respectively equal to -0.65% and -1.503%, for the BL and TL. Next, a rotating-analyzer spectroscopic ellipsometry system measures the following parameters (Ψ and Δ) for different incidence angles from 45 to 70° as shown in Figure B. These parameters are then coupled with an optical model to allow for an accurate determination of the complex dielectric (ε=ε1+iε2) of the sample. The developed optical model is presented in Figure A where the different constituting layers are shown: GeSn(BL/ML)/ Ge(VS)/Si. Furthermore, two additional surface layers were introduced to simulate the surface roughness as well as the presence of the native GeO2 oxide. The optical properties of the GeO2 oxide were used in their tabulated form from Reference [5]. The optical model is shown as a dashed line in Figure B, and the accuracy is measured by a very low MSE of 0.598. Consequently, the dielectric constant can be extracted. Having extracted the dielectric constant from the ellipsometry measurement, it becomes now possible to quantify the contributions from the E1, E1 + Δ1, E0’, E2, and E1’ critical points in the joint density of electronic states which they will be enhanced by computing numerical second derivatives of the already measured dielectric function. The numerical second derivative is often coupled with the Savitsky-Golay smoothing filter to reduce noise while maintaining the shape and the height of waveform peaks. The resulting lineshapes were fitted with model expressions from which the critical point energies Ej, amplitudes, broadenings Aj, and phases ϕj were determined. The model lineshapes have been well established in literature. [6] In Figure C, a lineshape fit for the E2 critical point energy for the Bottom layer (BL) was undertaken. The accuracy of the fit was confirmed with a coefficient of determination (R2) higher than 0.97. The Levenberg-Marquardt fit gave an E2 energy of 4.06±0.20 eV for the BL, whereas for the Top layer (TL), E2 was equal to 4.10±0.30 eV. After finding the energy for each sample, it becomes possible to map the effect of strain on the bang gap energies. Based on these systematic studies, this presentation will describe the individual influence of strain and composition on the optical properties of Sn-rich GeSn semiconductors.

High-Temperature Specific Heat of the TmBiGeO5 and YbBiGeO5 Compounds

The TmBiGeO5 and YbBiGeO5 compounds have been synthesized from Tm2O3 (Yb2O3), Bi2O3, and GeO2 oxides by the solid-state synthesis with successive burning at 1003, 1073, 1123, 1143, 1173, and 1223 K. High-temperature specific heat of the oxide compounds has been measured by differential scanning calorimetry. Basing on the experimental dependences Cp = f(T), the thermodynamic properties of the oxide compounds, i.e., the enthalpy and entropy variations, have been calculated.

Optical constants of germanium and thermally grown germanium dioxide from 0.5 to 6.6eV via a multisample ellipsometry investigation

Thermal GeO2 oxides up to 136 nm thickness were produced by annealing Ge wafers in pure oxygen at 550 °C and 270 kPa pressure for up to 10 h. The oxidation kinetics followed the Deal–Grove law. Using multisample spectroscopic ellipsometry for a series of five thermal oxides with different thicknesses, the complex dielectric functions of Ge and GeO2 were determined from 0.5 to 6.6 eV, for thin-film metrology applications in Ge-based microelectronics and photonics. The dispersion of the GeO2 layer was modeled with a simple Tauc-Lorentz oscillator model, but a more complicated dispersion with eight parametric oscillators was required for Ge. A reasonable fit to the ellipsometric angles could be obtained by assuming that all thermal oxides can be described by the same dielectric function, regardless of thickness, but a slight improvement was achieved by allowing for a lower density oxide near the surface of the thickest films. The authors compare their results with literature data for Ge and bulk and thin-film GeO2.

Physics of Metal/Ge Interfaces; Interface Defects and Fermi-Level Depinning

Germanium (Ge) has high carrier mobility compared to Si and is expected again to work as a promising key material in next-generation high-speed energy-saving devices. With respect to metal/Ge interfaces, however, there still exist serious issues to be overcome for applications; one which is the control of interface disorders and Schottky-barrier height (SBH). In this work, we discuss this issue based on fundamental properties of metal/Ge interfaces evaluated by theoretical calculations. It is well known that a variety of metal/Ge interfaces show a strong Fermi-level pinning (FLP); the Fermi energies of various metals are located at similar energy positions around the valence-band edge of Ge irrespective of the kind of metal, which induces the difficulty in controlling the SBH by simply changing the kind of metal. By the first-principles calculations, we found that this FLP is caused by the small band gap of Ge and the long penetration depth of metal-induced gap states (MIGS) into Ge layers even at clean interfaces [1]. Moreover, by evaluating the formation energies of various defects and dynamical atom motions around the interface, we showed that the MIGS are well hybridized with electronic states of defects and become the leading actors to increase the interface disorders (See Fig.1 in attached file for the case of vacancy defect in Ge layers). This result indicates important concept that the MIGS promote the disorder-induced gap states (DIGS). Correspondingly, even at weakly FL-depinned Fe3Si/Ge interface, the interface defects also promote the FLP [2]. One of recipes to release the FLP is to insert the third materials into the interfaces by the segregation of dopant atoms such as S and P, similar to the cases of metal/Si interfaces [3], and by the stacking of transition layers made of semiconductor/oxide. For example, we found that the appearance of ultrathin semiconducting α-Sn layers between metallic β-Sn and Ge layers works to increase the SBH for hole carriers, in agreement with recent experiments. Similarly, when GeO2 oxide is produced between metal and Ge layers, the MIGS penetration into Ge layers is prohibited and the SBH increases to the original position (See Fig.2 in attached file for the case of Al/Ge interfaces). These results are discussed in details, together with reviewing recent experiments and focusing on the fundamental physics at metal/Ge interfaces. <references>[1] T. Hiramatsu et al., Jpn. J. Appl. Phys. 53, 058006 (2014).[2] K. Kobinata and T. Nakayama, Jpn. J. Appl. Phys. 53, 035701 (2014).[3] T. Nakayama and K. Kobinata, Thin Solid Films 520, 3374 (2012). Figure 1

Atomistic Model for Ge Condensation under SiGe Oxidation

Oxidation of a dilute Si(Ge) alloy is modeled using an original protocol based on molecular dynamicssimulation and rules for the oxygen insertions. These rules, deduced from ab-initio calculations,favor the formation of SiO2 against GeO2 oxide which leads to segregation of Ge atoms into the alloyduring the oxidation front advance. Ge condensation is then observed close to the SiO2/Ge interfacedue to the strain induced by oxidation in this region. From the analysis of the simulations process, wepropose a one-dimensional description of Ge condensation which reproduces the evolution of the Geconcentration during oxidation of the SiGe alloy.

Raman-Brillouin scattering from a thin Ge layer: Acoustic phonons for probing Ge/GeO2 interfaces

We report on Raman–Brillouin scattering by acoustic phonons from a thin Ge layer. The high frequency acoustic phonons involved in this scattering are used to probe the native oxide present on top of the Ge layer. By comparing experiment and photoelastic modelling, a quantitative analysis is performed which shows that an interfacial layer is located in between the Ge and GeO2 oxide layers. The native oxide is found to be composed of a 0.5 nm thick interfacial layer and a 1 nm thick GeO2 layer on top of it. Sensitivity down to the sub-nm scale is evidenced.

Physical properties of Co/n-Ge Schottky contacts

To investigate the role of the interface state on the physical properties of Schottky contacts, Co/n-Ge Schottky diodes that have undergone various cleaning methods (HF etching and in situ thermal cleaning) were studied by transmission electron microscopy, deep-level transient spectroscopy and by a detailed analysis of the temperature dependence of the characteristics of the diodes. It is shown that Schottky barrier height characteristics are sensitive to the nature of the interface. The strongest Fermi level (FL) pinning and the highest spatial inhomogeneities are observed for intimate metal/semiconductor contacts. The presence of a thin oxide interlayer, even of Ge native oxide, allows the FL to be released towards the conduction band and leads to more homogeneous contacts. Finally, our results suggest that a pure GeO2 oxide interlayer should present a better depinning efficiency than the native Ge oxide.

Topological characteristics of bonds in SiO2 and GeO2 oxide systems upon a glass-liquid transition

Using the Angell model of broken bonds (configurons), configuron clustering in a topologically disordered lattice (network) of amorphous SiO2 and GeO2 upon a glass-liquid transition is considered. It is shown that the glass-liquid transition is accompanied by the formation of a macroscopic (percolation) configuron cluster penetrating the entire bulk of the material and possessing fractal geometry. The glass-liquid (overcooled liquid) percolation phase transition in the amorphous substance is accompanied by a change in the Hausdorff dimension of the bond network structure for configurons from the three-dimensional Euclidean dimension in the glassy state to a fractal dimension of 2.55 ± 0.05 in the liquidlike state. Contrary to the kinetic character of the liquid-glass transition, the glass-transition temperature is a thermodynamic parameter of the amorphous substance, depending parametrically on the cooling rate.

Phase equilibria in partially open systems under pressure: the decomposition of stoichiometric GeO2 oxide

The behavioral peculiarities of a highly compressed substance in partially open thermodynamic systems is discussed. Unlike for their closed counterparts, for open systems the time factor and effective pressure differences between various parts of the system should be taken into account. This proves to be relevant to many high-pressure experiments and especially so to geophysics, where celestial bodies are not closed systems with respect to their components. To demonstrate theunusual behavior of partially open systems, results on thedecomposition of the stoichiometric GeO2 oxide under heatingand pressure are presented. It is shown that under a moderatepressure of 100 kbar or less, in most cases the high entropy ofthe volatile component is the determining factor for the plausible decomposition reaction of compounds involving light elements, whereas at megabar pressures the ratio of specific volumes of the reaction components becomes more important. The results of the work suggest that the decomposition of compounds with volatile components at ultrahigh pressures and high temperatures might be a source of gaseous planetary atmospheres. In particular, the decomposition of Fe, Si, and Mgoxides in the Earth interior can serve as an additional geologicalsource of oxygen beyond the familiar biogenic source. An alternative model for the formation of the Earth metal core is proposed within the framework of this hypothesis.

Structural characterization of non-crystalline materials by the anomalous X-ray scattering(AXS) method.

The fundamentals of anomalous X-ray scattering (AXS) and its potential power have been described with respect to the determination of the local chemical environment around a specific element as a function of radial distance in multi-component non-crystalline materials. The usefulness of this relatively new method using the anomalous dispersion effect of X-rays has been demonstrated by some selected examples of GeO2 oxide glass, Al–Ge–Mn metallic glass, and Bi2O3–CaO–Fe2O3 thin film oxide glass grown on a Si substrate. The feasibility study for crystalline materials by applying this AXS method was also given using the results of a high temperature oxide superconductor of Y–Ba–Cu–O, as an example.

Characterisation of n -channel germanium MOSFET with gate insulator formed by high-pressure thermal oxidation

N-channel Ge MOSFETs are fabricated with the use of a double-layer gate oxide consisting of electron beam evaporated SiO2 over a native GeO2 oxide, formed by highpressure thermal oxidation. Interface properties of the MOS structure, determined by capacitance/voltage and mobility measurements, are shown to be suitable for FET devices.

The crystallization of cadmium germanates in aqueous solutions of sodium hydroxide and sodium chloride under hydrothermal conditions

AbstractThe crystallization in GeO2‐NaCl‐H2O, CdO‐NaOH(NaCl)–H2O. CdO–GeO2–H2O, CdO–GeO2–NaOH (NaCl)–H2O systems investigated under hydrothermal conditions depending on the initial ratio of CdO and GeO2 oxides in starting material and solvent concentration. Single crystals of six Cd‐germanates and five accessory compounds are obtained. The influence of the mineralizer on Cd‐germanates crystallization and the chemism of the interaction of the charge components and the solvent are discussed.