Ternary Ge Research Articles

Study of SiGeAsTe and SiGeAsSe chalcogenide thin films by Raman spectroscopy and understanding of their OTS properties

In this paper, a range of sputtered ternary and quaternary (Si)(Ge)AsxTe3 layers (x: 2 or 5) and (Si)(Ge)As2Se3 layers are examined using Raman spectroscopy. The results are linked to the Ovonic Threshold Switching properties of these materials when incorporated in selector devices, as observed in separate studies. In case of both the As-rich and As-poor tellurides, a large amount of homopolar bonds are present as the spectra are dominated by peaks associated with As–As and Te–Te bonds. Such homopolar bonds are commonly linked with drift in OTS properties. In the case of the selenides the spectra are dominated by modes associated with heteropolar As–Se bond vibrations. Adding Ge as an alloying element has a significant impact on the bond structure for both material systems. In contrast, Si has a much less pronounced impact and will mostly bond with itself. Time-resolved Raman measurements were also performed to determine the stability of the layers under micro-Raman laser excitation. At the regular exposure settings, no significant changes in the spectra were observed during the measurement. At elevated exposure settings, however, persistent changes in the bond structure can be induced for certain compositions.

Co2@(Ge17Ni)]4-: the first edge-sharing double-cage endohedral germanide.

We report here a new double-cage endohedral Ge cluster, [Co2@(Ge17Ni)]4-, fused through two [Co@(Ge9Ni)] moieties with a shared Ni-Ge edge. This ternary Co-Ge-Ni species not only represents the first double-cage example of an 18-vertex Zintl cluster, but also fills in the missing link of the edge fusion model in the double-cage systems.

Thermodynamic modelling of the binary indium-lithium system, a promising li-ion battery material

The binary In ? Li system is a promising Li-ion battery anode material as well as a part of the important ternary Ge ? In ? Li system. The thermodynamic descriptions of metallic systems are widely used to retrieve information necessary for alloy applications. In this work, a thermodynamic model of a binary indium ? lithium system prepared by the Calphad approach is proposed. The liquid phase was described by an associate model, and the solid phases determined by the ab-initio calculation were included in the thermodynamic modeling. The obtained set of self-consistent thermodynamic parameters well reproduces the available experimental data and enables further calculations of multi-component systems. A good agreement between the calculations and the available experimental data was found. The proposed model can be used for further descriptions of ternary systems.

Unraveling the Atomic Structure of Bulk Binary Ga-Te Glasses with Surprising Nanotectonic Features for Phase-Change Memory Applications.

Binary Ge-Te and ternary Ge-Sb-Te systems belong to flagship phase-change materials (PCMs) and are used in nonvolatile memory applications and neuromorphic computing. The working temperatures of these PCMs are limited by low-T glass transition and crystallization phenomena. Promising high-T PCMs may include gallium tellurides; however, the atomic structure and transformation processes for amorphous Ga-Te binaries are simply missing. Using high-energy X-ray diffraction and Raman spectroscopy supported by first-principles simulations, we elucidate the short- and intermediate-range order in bulk glassy GaxTe1-x, 0.17 ≤ x ≤ 0.25, following their thermal, electric, and optical properties, revealing a semiconductor-metal transition above melting. We also show that a phase change in binary Ga-Te is characterized by a very unusual nanotectonic compression with the high internal transition pressure reaching 4-8 GPa, which appears to be beneficial for PCM applications increasing optical and electrical contrast between the SET and RESET states and decreasing power consumption.

Obtaining glasses in the extremely crystallizing Ge–Sb–Te phase change material

Using thermal co-evaporation techniques, we show that various glassy compositions can be obtained along the GexSbxTe100-2x join in the ternary Ge–Sb–Te system which is known to display dramatic crystallization tendencies. Earlier attempts to produce bulk glasses have been limited to Sb-poor compositions close to the eutectic GeTe6. Results indicate a weak variation of Tg with composition x and also a thermal stability that is weak for most systems, and especially for compositions close to the domain where Ge2Sb2Te5 can be formed. Our results are put in perspective with other network-forming chalcogenides and the Tg variation suggests the preferential formation of Te–Sb–Te, at variance with isochemical compounds such as Ge–Sb–Se. Data are discussed within the framework of topological based approaches which not only indicate that optimal glass formation is achieved for compositions satisfying the Maxwell stability criterion but also predict a flexible to rigid transition at x=8.5%. Most of our glasses could be formed around this composition.

Phase-field modeling of the non-congruent crystallization of a ternary Ge–Sb–Te alloy for phase-change memory applications

The ternary alloy of germanium, antimony, and tellurium (GST) is widely used as a material for phase-change memories. In particular, the stoichiometric compound Ge2Sb2Te5 exhibits a rapid congruent crystallization. To increase the temperature at which spontaneous crystallization erases the stored information, alloys that are enriched in germanium have been investigated. Their crystallization is accompanied by segregation and eventually the nucleation of a new, germanium-rich phase. In order to model the redistribution of alloy components and the time evolution of the microstructure during device operations, we develop a multi-phase-field model for the crystallization of GST that includes segregation and couple it with orientation fields that describe the grain structure. We demonstrate that this model is capable to capture both the emergence of a two-phase polycrystalline structure starting from an initially amorphous material, and the melting and recrystallization during the SET and RESET operations in a memory cell of the “wall” type.

Physical and mechanical properties of intermediate phase chalcogenide glasses with centroid compositions in the Ge-Te-In-Ag system

The optical and mechanical properties of three Te-based chalcogenide glasses, whose compositions correspond to the intermediate phase centroids in their respective binary Ge–Te, ternary Ge–Te–In and quaternary Ge–Te–In–Ag systems, were evaluated using micro-Raman and ultraviolet–visible spectroscopies, and nanoindentation. Results show a blueshift and an increase in the full width at half maxima for the most dominant Raman peak, and a decrease in the optical band gap, with successive doping of Ge15Te85 with In and Ag, which are attributed to the increased network connectivity and defect density, respectively, with doping. Nanoindentation results show that both the elastic modulus and the hardness increase with successive doping because of the enhancement in the network connectivity. Dynamic mechanical analysis shows that the storage modulus increases with frequency, indicating the dominance of the viscous part, while loss modulus and internal friction are relatively low in the binary system than the quaternary system. The measured indentation fracture toughness increases from binary to quaternary glass because of the crack deflection aided by the enhanced network connectivity.

Evaluation of nuclear radiation shielding competence for ternary Ge–Sb–S chalcogenide glasses

Chalcogenide glasses are which include germanium, antimony, and sulfur in its structure. The high physical, dielectric, optical, mechanical, and thermal features of the chalcogenide glasses lead to the occasion to evaluate its radiation shielding characteristics. Gamma ray and neutron shielding parameters were evaluated for five chalcogenide glasses doped with CdCl2 according to the formula 60(GeS2)–(40 − x)Sb2S3–xCdCl2; x = 0, 10, 20, 30, and 40 mol% glasses. The mass attenuation coefficient MAC for chalcogenide glasses was simulated using Monte Carlo simulation code (MCNP-5) in gamma photon energy between 0.015 and 15 MeV. The obtained results showed that the MAC for all studied glasses decreases with insertions of CdCl2. The highest MAC is obtained for GSC glasses without CdCl2 content and varied between 0.037 and 4.706 cm2 g−1, while the lowest MAC achieved for GSC 40 glasses with (40 mol%) CdCl2 and varied between 0.034 and 44.758 cm2 g−1. After that, the simulated MAC for all chalcogenide glasses is compared with those calculated theoretically using XCOM software. Other pivotal gamma ray shielding competences such as half value layer, mean free path and effective atomic number (Zeff), and exposure buildup factor for the chalcogenide glasses were also evaluated via the μ/ρ. Furthermore, the fast neutron removal cross section (ΣR) was also evaluated for chalcogenide glasses. GSC0 possesses the best removal cross section for fast neutron (ƩR = 0.0695 cm−1) among the present chalcogenide glasses.

Third-order optical nonlinearity properties of CdCl2-modifed Ge–Sb–S chalcogenide glasses

We developed a new type of chalcohalide glasses with physicochemical and nonlinear optical properties that are tunable by composition. It is found that more than 60 mol.% CdCl2 heavy metal halide can be dissolved into the ternary Ge–Sb–S system and forming stable glasses. The visible-light transparency range is extended to shorter wavelengths with the addition of CdCl2, which is beneficial for the optical quality control and infra-red (IR) system alignment. The third-order optical nonlinearity (TONL) is studied using the femtosecond Z-scan method. The results show that both the nonlinear refractive index and two photon absorption co-efficient decrease with CdCl2. Benefiting from the favorable property-tailoring effects of CdCl2, the TONL figure of merit (FOM) can be improved to meet the requirement (FOM < 1) for all-optical switching and IR photonic applications.

The role of Mn doping on the electrical and mechanical properties of Ge–Se–Mn glasses

The present study concerns the impact of adding Mn content on the electrical, thermoelectrical, and mechanical properties of ternary Ge–Se–Mn glassy materials. The activation energies for the electric (ΔEdc) and thermoelectric (ΔEth) conduction of different compositions of $$ \left( {{\text{Ge}}_{1} {\text{Se}}_{2} } \right)_{100 - x} {\text{Mn}}_{x} \left( {0.0 \le x \le 12.0 \;{\text{at}}.\% .} \right) $$ thin films were estimated. The elastic moduli such as longitudinal (L-), shearing (S-), young (Y-), and bulk (K-) modulus as well as microhardness (H), Poisson’s ratio (σ), and Debye temperature (TD) for the studied glasses were investigated. The obtained values of ΔEdc, ΔEth, and the molar volume were decreasing, whereas the glass density, L, S, Y, K, H, σ, and TD, were increasing with increasing Mn content. The values of K were correlated with the electronegativity ($$ \Delta \chi $$) and the bandgap (Eg = 2 (ΔEdc)). Eg decreased from 1.737 to 1.421 eV with increasing the Mn content from 0 to 12 at. %. The estimated values of K based on $$ \Delta \chi $$ and/or Eg are found in excellent agreement with that experimentally determined. The obtained results were discussed in terms of the electronic polarizability.

Fabrication of ternary Ge–Se–Sb chalcogenide microlens arrays using thermal reflow

Ternary Ge–Se–Sb chalcogenide glasses have attractive optical properties for fabrication of micro optical components. This paper reports a thermal reflow method to fabricate Ge–Se–Sb chalcogenide microlens arrays (MLAs). By heating the chalcogenide to melting state, the surface tension of the melting chalcogenide contracts the liquid chalcogenide into spherical shape, forming microlenses automatically. Key processes including chalcogenide evaporation, dry etching, and thermal reflow temperature and time are investigated systematically, and microlenses with smooth surfaces, uniform profiles, and small F numbers have been fabricated successfully using the optimized processes. These preliminary results demonstrate the feasibility of using thermal reflow as a simple and low cost method to fabricate Ge–Se–Sb chalcogenide microlenses. The process parameters and the key influencing factors can be used as a baseline for process optimization.

Thermochemical properties and glass forming tendency modeling for the ternary Ge–Mn–Gd melts

Information on the thermochemical properties may be useful for predicting of the concentration regions of easy glass formation in multicomponent alloys. In present investigation the integral enthalpies of mixing for the Ge–Mn–Gd melts were determined for the entire concentration interval at 1830 K using the Redlich-Kister-Muggianu method. GFT values for binary and ternary alloys of this system were calculated. Size mismatch entropy was estimated within the frameworks of hard spheres model. On the basis of performed calculations the concentration regions in which the melts of the Ge–Mn–Gd system can demonstrate considerable tendency to easy glass formation were suggested.

Atomic Layer Deposition of GeTe and Ge–Sb–Te Films Using HGeCl3, Sb(OC2H5)3, and {(CH3)3Si}2Te and Their Reaction Mechanisms

In this paper, a new atomic layer deposition (ALD) process for depositing binary GeTe and ternary Ge–Sb–Te thin films is reported, where HGeCl3 and ((CH3)3Si)2Te were used as Ge and Te precursors, respectively. The precursors reacted together to form the films at a low substrate temperature of 50–100 °C, without involving any additional reactive process gas. HCl elimination from the Ge precursor to form the divalent Ge intermediate, GeCl2, is proposed to explain the formation of 1:1 composition stoichiometric GeTe films. The GeTe films are promising for use in phase change memory applications. Ternary Ge–Sb–Te films were deposited by combining the GeTe ALD process with a previously developed ALD process for Sb2Te3 films, where Sb(OC2H5)3 and ((CH3)3Si)2Te were employed respectively as the Sb and Te precursors. However, the composition of the ternary GeSbTe films deviated slightly from the desired GeTe–Sb2Te3 pseudobinary composition suggesting that a certain unwanted reaction was involved between the prev...

Optical transmittance and reflectance studies and evidence of weak electron–phonon interaction in Type-I Ge clathrate Ba8Ga16Ge30

The optical properties of ternary type-I Ge clathrate Ba8Ga16Ge30 are investigated by optical reflectance and transmittance measurements. The refractive index and extinction coefficient are calculated from the reflectance spectrum via the modified Kramers–Kronig analysis method between 0.5 and 3.2 eV. The photon energy dependence of the optical absorption coefficient reveals that Ba8Ga16Ge30 is an indirect band gap semiconductor with a gap energy Eg of 0.69 eV at 5.7 K and 0.66 eV at 285 K. The temperature dependence of Eg can be satisfactorily described by an equation based on the Bose–Einstein statistics model. When compared with those of common elemental, III–V, and II–VI semiconductors, the small temperature coefficient dEg/dT of the Ba8Ga16Ge30 can be considered to represent the weak electron–phonon interaction in the Ba8Ga16Ge30 clathrate.

PHASE EQUILIBRIUM IN YbTe–Yb3Ge5 SYSTEM

For citation:Mukhtarova Z.M. Phase equilibrium in Ybte–Yb3Ge5 system. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 1. P. 64-67.Study of properties of semiconductors developed in close connection with their technical applications. The present work was devoted to study of phase equilibria and character of interaction in YbTe–Yb3Ge5 system. The section of YbTe–Yb3Ge5 in ternary system Ge–Te–Yb is not only scientific, but also practical interest. The section of YbTe–Yb3Ge5 was studied by methods of physical-chemical analysis: differential-thermal (DTA), high temperature differential-thermal (HTDT), X-ray phase, microstructural analysis (MSA), as well as measurement of density and micro hardness. DTA was performed with pyrometer HTP-75 in quartz ampoule pimped off till 0.1333 Pa. HTDT was performed with HTDT-8m (Tmelt.≥1500÷2000K) by analogical method. X-ray phase analysis was performed by powder method with X-ray diffractometer DRON-2 (CuKα- radiation with Ni-filter). MSA was performed with microscope MIM 8. Micro hardness of alloys was measured with micro hardness tester PMT-3.Density of alloys was determined by pycnometer test. During investigations of the system we used germanium B–4, tellurium B–3, ytterbium Yb–1. Alloys were synthesized at 1450–1700 K temperature range and at this temperature ampoule was kept 5–6 h. Cooling was performed slowly. DTA shows that on thermograms of alloys of the system have two effects. Obtained effects are endothermic reversible.For confirming the data of DTA, microstructural analysis, as well as measurement of micro hardness were performed with X-ray analysis. As the data show, at the concentration of 15–80 mol% of Yb3Ge5 monotectic conversion occurs which is confirmed with isothermal line at 1025 K. Thus, it was established that the section of 4YbTe–Yb3Ge5 is quasibinary cross-section of ternary system Ge–Te–Yb and its diagram is related to eutectic type with monotectics.Eutectic of the system 4YbTe–Yb3Ge5 corresponds to composition of 85% mol% of Yb3Ge5 and temperature of 915 K.

Experimental Realization of a Ternary-Phase Alloy Through Microwave-Activated Annealing for Ge Schottky pMOSFETs

This paper presents a high-performance Ge p-channel MOSFET (pMOSFET) with NiGePt as a ternary-phase alloy of Schottky source/drain (S/D) formed through low-temperature microwave-activated annealing (MWA). We fabricated a NiGePt alloy contact with uniform crystallinity through structural engineering and MWA. We clarified the phenomena of thermal reaction and diffusion for forming ternary-phase alloys using MWA properties such as thermal dynamics and ionic transportation. The ternary-phase NiGePt alloy is crucial for improving the off-leakage current of the junction. A lower process temperature is beneficial for eliminating surface roughness and reducing alloy agglomeration of the Schottky contact S/D. Consequently, the fabricated NiGePt/n-Ge Schottky junction exhibited a high effective barrier height ( $\Phi _{{{\textrm {Bn}}}})$ of 0.59 eV, resulting in a high junction current ratio of more than $10^{5}$ at an applied voltage of $|V_{a}| = 1$ V. In addition, we exploited the advantages of low-temperature microwave annealing to fabricate the pMOSFET, which includes a GeO2 passivation layer and a Schottky S/D. Our ternary Schottky Ge pMOSFET ( $L = 4~\mu \text{m}$ ) exhibited high $I_{{\mathrm{\scriptscriptstyle ON}}}/I_{{\mathrm{\scriptscriptstyle OFF}}}$ ratios of approximately $3.7 \times 10^{3}$ ( $I_{D})$ and $1.3 \times 10^{5}$ ( $I_{S})$ and a moderate subthreshold swing of 126 mV/dec.

Development of thermally stable and moldable chalcogenide glass for flexible infrared lenses

Abstract

Thermal properties of ternary Ge–Sb–Se chalcogenide glass for use in molded lens applications

As for the molded lens applications of ternary Ge–Sb–Se glass, Ge-rich compositions are normally preferable since thermal and mechanical properties are better in these compositions. In an effort to explicate thermal properties of such glasses suitable for practical molding process, we have evaluated their compositional dependence of glass transition temperature (Tg) and softening point temperature (Ts). Among three constituent atoms, Ge turns out to exert a most conspicuous correlation with Tg and Ts. This phenomenological behavior is then explained in connection with structural evolution induced by Ge. Based on analysis of mean coordination number and average bond energy, it is inferred that the glass structure becomes energetically more stable and topologically more connected with increasing Ge content.

Ternary and quaternary Ni(Si)Ge(Sn) contact formation for highly strained Ge p- and n-MOSFETs

The formation of new ternary NiGeSn and quaternary NiSiGeSn alloys has been investigated to fabricate metallic contacts on high Sn content, potentially direct bandgap group IV semiconductors. (Si)GeSn layers were pseudomorphically grown on Ge buffered Si(001) by reduced pressure chemical vapor deposition. Ni, i.e. the metal of choice for source/drain metallization in Si nanoelectronics, is employed for the stano-(silicon)-germanidation of highly strained (Si)GeSn alloys. We show that NiGeSn on GeSn layers change phase from well-oriented Ni5(GeSn)3 to poly-crystalline Ni1(GeSn)1 at very low annealing temperatures. A large range of GeSn compositions with Sn concentrations up to 12 at.%, and SiGeSn ternaries with large Si and Sn compositions from 18%/3% to 4%/11% are investigated. In addition, the sheet resistance, of importance for electronic or optoelectronic device contacts, is quantified. The incorporation of Si extends the thermal stability of the resulting low resistive quaternary phase compared to their NiGeSn counterparts.

Thermodynamic study of the Ge–Mn–Si system

Among the potential materials for thermoelectric applications, higher manganese silicides (HMS) MnSix (with x around 1.75) exhibit interesting figures-of-merit at intermediate temperatures (573–873K). Moreover it appears that the figure-of-merit can be improved by germanium doping. The optimization of the elaboration of such alloys needs the knowledge of the ternary Ge–Mn–Si system.The solid–solid equilibrium in the ternary system seems to be highly driven by the D88 phase an isostructural form of Mn5Si3 and Mn5Ge3. However, the existence of a complete solid solution between these two compounds is not clearly established in the literature. First principles calculations are performed to clarify the mixing enthalpies in this potential solid solution. The predicted phase separation at low temperature is then experimentally confirmed by metallographic examinations on 3 annealed samples.On the basis of these new data, a thermodynamic description of the ternary system is performed using the Calphad method.