Germanium Antimony Research Articles

Thermoelectric properties of c-GeSb0.75Te0.5 to h-GeSbTe0.5 thin films through annealing treatment effects

Germanium–Antimony–Tellurium (Ge–Sb–Te) thin films were deposited on silicon wafers with 1-μm silicon dioxide (SiO2/Si) by pulsed dc magnetron sputtering from a 99.99% GeSbTe target of 1:1:1 ratio at ambient temperature. The samples were annealed at 573, 623, 673, and 723 K for 3600 s in a vacuum state. The effects of the annealing treatment on phase identification, atomic composition, morphology and film thickness, carrier concentration, mobility, and Seebeck coefficient of the Ge–Sb–Te samples have been investigated by grazing-incidence X-ray diffraction, auger electron spectroscopy, field-emission scanning electron microscopy, Hall-effect measurements, and steady state method, respectively. The results demonstrated that the as-deposited Ge–Sb–Te sample was amorphous. Atomic composition of as-deposited and annealed films at 573 K and 623 K were GeSb0.75Te0.5 while annealed films at 673 K and 723 K were GeSbTe0.5 due to Sb-rich GeSb0.75Te0.5. The samples annealed at 573 K and 623 K showed the crystal phases of cubic structure (c-GeSb0.75Te0.5) into hexagonal structure (h-GeSbTe0.5) after annealing at 673 K and 723 K. The study demonstrated the insulating condition from the as-deposited GeSbTe film, and the changes towards the thermoelectric properties from the annealing treatments. The GeSbTe films annealed at 673 K yielded excellent thermoelectric properties with the electrical resistivity, Seebeck coefficient, and power factor at approximately 1.45 × 10−5 Ωm, 71.07 μV K−1, and 3.48 × 10−4 W m−1 K−2, respectively.

Microstructure-dependent DC set switching behaviors of Ge–Sb–Te-based phase-change random access memory devices accessed by in situ TEM

Phase-change random access memory (PCRAM) is one of the most promising nonvolatile memory devices. However, inability to secure consistent and reliable switching operations in nanometer-scale programing volumes limits its practical use for high-density applications. Here, we report in situ transmission electron microscopy investigation of the DC set switching of Ge–Sb–Te (GST)-based vertical PCRAM cells. We demonstrate that the microstructure of GST, particularly the passive component surrounding the dome-shaped active switching volume, plays a critical role in determining the local temperature distribution and is therefore responsible for inconsistent cell-to-cell switching behaviors. As demonstrated by a PCRAM cell with a highly crystallized GST matrix, the excessive Joule heat can cause melting and evaporation of the switching volume, resulting in device failure. The failure occurred via two-step void formation due to accelerated phase separation in the molten GST by the polarity-dependent atomic migration of constituent elements. The presented real-time observations contribute to the understanding of inconsistent switching and premature failure of GST-based PCRAM cells and can guide future design of reliable PCRAM. Using in situ electron microscopy, researchers in Korea have discovered why phase-change memory devices can fail during switching operations. Phase-change materials, such as germanium–antimony–tellurium (Ge–Sb–Te) alloys, rapidly switch between crystalline and amorphous phases on electrical heating. Researchers have used this to make memory chips that are hundreds of times faster than flash devices, but inconsistent performance currently limits practical, high-density applications. Sang Ho Oh from Pohang University of Science and Technology and colleagues observed the phase changes of Ge–Sb–Te memory cells in real time by applying direct-current voltages through a transmission electron microscope. They found that the device lifetime critically depended on the atomic microstructure around the active switching site. Ironically, higher degree of crystallinity of this passive zone can cause more excessive heat dissipation, leading to eventual melting and evaporation of cells. Applying in situ TEM techniques to GST-based vertical PCRAM cells, we directly observed the DC set switching process of real devices for the first time. The results show that the microstructure of crystalline GST matrix is an important structural parameter determining the local temperature distribution. In the case of highly crystallized GST matrix, the device failure occurred via two-step void formation due to the polarity-dependent electromigration.

Anodes for sodium ion batteries based on tin-germanium-antimony alloys.

Here we provide the first report on several compositions of ternary Sn-Ge-Sb thin film alloys for application as sodium ion battery (aka NIB, NaB or SIB) anodes, employing Sn50Ge50, Sb50Ge50, and pure Sn, Ge, Sb as baselines. Sn33Ge33Sb33, Sn50Ge25Sb25, Sn60Ge20Sb20, and Sn50Ge50 all demonstrate promising electrochemical behavior, with Sn50Ge25Sb25 being the best overall. This alloy has an initial reversible specific capacity of 833 mAhg(-1) (at 85 mAg(-1)) and 662 mAhg(-1) after 50 charge-discharge cycles. Sn50Ge25Sb25 also shows excellent rate capability, displaying a stable capacity of 381 mAhg(-1) at a current density of 8500 mAg(-1) (∼10C). A survey of published literature indicates that 833 mAhg(-1) is among the highest reversible capacities reported for a Sn-based NIB anode, while 381 mAhg(-1) represents the optimum fast charge value. HRTEM shows that Sn50Ge25Sb25 is a composite of 10-15 nm Sn and Sn-alloyed Ge nanocrystallites that are densely dispersed within an amorphous matrix. Comparing the microstructures of alloys where the capacity significantly exceeds the rule of mixtures prediction to those where it does not leads us to hypothesize that this new phenomenon originates from the Ge(Sn) that is able to sodiate beyond the 1:1 Na:Ge ratio reported for the pure element. Combined TOF-SIMS, EELS TEM, and FIB analysis demonstrates substantial Na segregation within the film near the current collector interface that is present as early as the second discharge, followed by cycling-induced delamination from the current collector.

Deposition and Characterization of CVD-Grown Ge-Sb Thin Film Device for Phase-Change Memory Application

Germanium antimony (Ge-Sb) thin films with tuneable compositions have been fabricated on SiO2/Si, borosilicate glass, and quartz glass substrates by chemical vapour deposition (CVD). Deposition takes place at atmospheric pressure using metal chloride precursors at reaction temperatures between 750 and 875°C. The compositions and structures of these thin films have been characterized by micro-Raman, scanning electron microscope (SEM) with energy dispersive X-ray analysis (EDX) and X-ray diffraction (XRD) techniques. A prototype Ge-Sb thin film phase-change memory device has been fabricated and reversible threshold and phase-change switching demonstrated electrically, with a threshold voltage of 2.2–2.5 V. These CVD-grown Ge-Sb films show promise for applications such as phase-change memory and optical, electronic, and plasmonic switching.

Characterization of In20Ge15Sb10Te55 Phase Change Material for Phase Change Memory with Low Power Operation and Good Data Retention

An indium-incorporated germanium–antimony–telluride material, In20Ge15Sb10Te55 (IGST), was investigated as a recording material for phase change memory. The crystallization temperature of IGST was 226 °C, which is 75 °C higher than that of conventional GST. The reset current of the device using IGST was about 10 mA for a plug 180 nm in diameter, which enabled a low-power operation, compared with the GST-based device. A cycle endurance of up to 1.5×104 was achieved. The data retention was estimated to be 10 years at 145 °C. These data clearly show that IGST exhibits promising characteristics as a recording material for phase change memory.

A Series of Novel Organically Templated Germanium Antimony Sulfides

A series of novel organically templated germanium antimony sulfides have been solvothermally synthesized and structurally, thermally, and optically characterized. The compound [Me(2)NH(2)](6)[(Ge(2)Sb(2)S(7))(Ge(4)S(10))] (1) features two distinct tetranuclear [Ge(2)Sb(2)S(7)](2-) and [Ge(4)S(10)](4-) isolated clusters. The compound [(Me)(2)NH(2)][DabcoH](2)[Ge(2)Sb(3)S(10)] (2) (Dabco = triethylenediamine) features a 1D-[Ge(2)Sb(3)S(10)](n)(3n-) ribbon constructed with two [GeSbS(5)](n)(3n-) chains bridged by Sb(3+) ion in psi-SbS(4) configuration. Compounds [M(en)(3)][GeSb(2)S(6)] (M = Ni (3), Co (4) en = ethylenediamine) feature the unique 2D grid layer structures of [GeSb(2)S(6)](n)(2n-). The compound [(Me)(2)NH(2)](2)[GeSb(2)S(6)] (5) previously reported by us features a 3D chiral microporous structure with the chiral channels. The optical absorption spectra indicate that all the compounds are wide bandgap semiconductors. Thermal stabilities of these compounds have been investigated by thermogravimetric analyses (TGA).

ChemInform Abstract: Three‐Dimensional Chiral Microporous Germanium Antimony Sulfide with Ion‐Exchange Properties.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Three‐Dimensional Chiral Microporous Germanium Antimony Sulfide with Ion‐Exchange Properties

Three‐Dimensional Chiral Microporous Germanium Antimony Sulfide with Ion‐Exchange Properties

Three‐Dimensional Chiral Microporous Germanium Antimony Sulfide with Ion‐Exchange Properties

Chiral hole: The first chiral microporous germanium antimony sulfide with 3D helical channels was constructed by the unprecedented combination of {GeS4} tetrahedra and ψ-{SbS4} trigonal bipyramids. The dimethylammonium cations present in the structure are easily exchanged with alkali metal cations present in aqueous solution. The title compound has high ion-exchange capacity and high selectivity for Cs+ ions.

Role of Ge Switch in Phase Transition: Approach using Atomically Controlled GeTe/Sb2Te3 Superlattice

Germanium–antimony–tellurite (GST) is a very attractive material not only for rewritable optical media but also for realizing solid state devices. Recently, the study of the switching mechanism between the amorphous and crystal states has actively been carried out experimentally and theoretically. Now, the role of the flip-flop transition of a Ge atom in a distorted simple-cubic unit cell is the center of discussion. Turning our viewpoint towards a much wider region beyond a unit cell, we can understand that GeSbTe consists of two units: one is a Sb2Te3 layer and the other is a Ge2Te2 layer. On the based of this simple model, we fabricated the superlattice of GST alloys and estimated their thermal properties by differential scanning calorimetry (DSC). In this paper, we discuss the proof of the Ge switch on the basis of thermo-histories.

Study of the ternary system germanium–antimony–tin: experimental phase diagram

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.

Temperature dependence of structure and electrical properties of germanium–antimony–tellurium thin film

The interest in the study of Ge:Sb:Te thin films is due to their use as optical and electrical memory materials. Both of these applications are based on the structural change from the amorphous to the crystalline state. Thus, understanding of the mechanism of crystallization in this material is important from basic and technological points of view. In this work we have studied the kinetics of the crystallization of Ge:Sb:Te films prepared by thermal evaporation. For that, in situ resistance and capacitance measurements during heating were used. The transformation kinetics from the amorphous to the crystalline state were analyzed using the Kissinger model, from which the activation energy of the crystallization process is obtained. Using x-ray diffraction, Raman spectroscopy and optical microscope measurements, we have observed that during heating at different heating rates, crystallization of the film is accompanied by the segregation of micrometric inclusions formed by amorphous tissue, perhaps some segregated impurities and crystalline tellurium particles. The number and size of these inclusions depend on the heating rate. From our measurements we found that the capacitance measurements is a sensitive method by which to analyze the crystallization process in thin films. It provides additional information not obtained using other methods.

Structural analysis and crystallization studies of germanium–antimony– tellurium sputtered films on different underlayers

Crystallization processes and structures were analyzed, by using modified dynamical reflectance spectroscopy, x-ray diffraction measurement, and transmission electron microscopy for a germanium–antimony–tellurium (Ge–Sb–Te) ternary amorphous film on different underlayer materials: a silicon nitride (Si3N4) film and a zinc sulfide–20 mol % silicon dioxide (ZnS–SiO2) film. The crystallization temperature was almost the same (about 430 K) for each sample. Above the crystallization temperature, the Ge–Sb–Te film on the Si3N4 underlayer film exhibited a face-centered-cubic (fcc) structure and grains grew gradually with transformation to a hexagonal structure, whereas the film on the ZnS–SiO2 underlayer film exhibited mixed phases of the fcc and hexagonal structure and abrupt grain growth at 520 K. These crystallization differences are thought to be caused by the interfacial atomic arrangement of amorphous Ge–Sb–Te. This arrangement depends on the chemical affinity at the interface.

Crystallization of germanium–antimony–tellurium amorphous thin film sandwiched between various dielectric protective films

Crystallization processes were studied for germanium–antimony–tellurium (Ge–Sb–Te) ternary amorphous thin film as a single layer or sandwiched between various dielectric films, such as silicon dioxide (SiO2), siricon nitride (Si3N4), tantalum oxide (Ta2O5), zinc sulfide (ZnS), and ZnS–20 mol % SiO2. The processes were analyzed quantitatively, based on transmittance changes in Ge–Sb–Te films heated either exothermally or isothermally. Both Kissinger equation and Johnson–Mehl–Avrami kinetic analysis were adopted to estimate activation energy and the reaction order of the processes. Ge–Sb–Te single-layer amorphous film crystallized in two stages, nucleation and crystal growth. These two processes can be distinguished by exothermal crystallization patterns. By sandwiching this film into dielectric films, crystallization activation energy increases and the nucleation processes are affected. The Si3N4 and Ta2O5 dielectric films accelerate the nucleation, while the SiO2 films inhibit it, and the ZnS and ZnS–20 mol % SiO2 films promote the nucleation even in the grain growth process. Wettability measurements indicate that surface reactivity and chemical affinity are the factors which produce this variation.

Copper ion-selective electrode based on a chalcogenide glass membrane

A chalcogenide glass membrane based on germanium–antimony–selenium and doped with 20.8% copper was used in the preparation of a copper ion-selective electrode (ISE). It shows an almost Nernstian response of 31 mV. It is specific in the presence of Na+, K+, Ca2+, Co2+, and Ni2+ with selectivity coefficients of 10–2 for Na+ and K+, and 10–3 for the other ions. For both UO22+ and Zn2+, the selectivity coefficient is 0.1, whereas for Al3+ and Fe3+ it is 0.06 and 0.5, respectively. Iron(II) interferes very strongly. The electrode response is independent of pH in the range 1–3. The copper ISE was used as an indicator electrode for the potentiometric titration of copper ions in solution (10–4–0.1 mol l–1) using standard ethylenediaminetetraacetic acid, a sharp potential change occurs at the end-point.

Correlation of Geiger Counter and Hall Effect Measurements in Alloys Containing Germanium and Radioactive Antimony 124

The distribution of the solute atoms in ingots of germanium antimony alloys which were prepared according to a prescribed cooling cycle have been measured. The solute was ${\mathrm{Sb}}^{124}$ and its distribution was measured with a Geiger counter. In addition, Hall measurements were made which show that in the impurity saturation range each antimony atom contributes one conduction electron. This makes it possible to determine the solute distribution in non-radioactive samples by the Hall method.