Increasing Ge Content Research Articles

Composition and strain analysis of Si1-xGex core fiber with Raman spectroscopy

The fabrication and characterization of Si1-xGex core fiber have attracted much attention because of its great application potential in new optoelectronic devices. In this work, by assembling two semi-cylindrical monocrystalline Si and Ge rods into a silica tube, we present a fabrication method to draw Si1-xGex core silica clad fiber with graphite furnace. Raman spectra analysis reveals that in all regions of the core formed the Si1-xGex alloy. The optical microscopic photograph shows that in the core of a diameter of 36 μm distributed the bright and dark regions, where it was further proved by Raman spectroscopy that the bright regions are Ge-rich areas and the dark regions are rich in silicon. By recording the Raman spectra of consecutive regions, it was found that with the increase of Ge content (x<0.5) the peak intensity of Si-Ge mode obviously increases, similar to the intensity of Ge-Ge mode, while the peak intensity of Si-Si mode decreases. Then we made a quantitative analysis of the components and strain by mapping the Raman spectra of the fiber core. The experimental results show that the Ge content mainly distributes between 0.1 and 0.8, concentrating between 0.2 and 0.3, and the strain distribution on the surface is obtained at the same time.

Anisotropic selective etching between SiGe and Si

In Si/SiGe dual-channel FinFETs, it is necessary to simultaneously control the etched amounts of SiGe and Si. However, the SiGe etch rate is higher than the Si etch rate in not only halogen plasmas but also physical sputtering. In this study, we found that hydrogen plasma selectively etches Si over SiGe. The result shows that the selectivity of Si over SiGe can be up to 38 with increasing Ge concentration in SiGe. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) results indicate that hydrogen selectively bonds with Si rather than with Ge in SiGe. During the etching, hydrogen-induced Si surface segregation is also observed. It is also observed that the difference in etched amount between SiGe and Si can be controlled from positive to negative values even in Si/SiGe dual-channel fin patterning while maintaining the vertical profiles. Furthermore, no plasma-induced lattice damage was observed by transmission electron microscopy for both Si and SiGe fin sidewalls.

Physical and electrical characteristics of GexSb100−x films for use as phase-change materials

In this study, we investigate a GeSb binary phase to be used as a high-speed phase-change material (PCM). In particular, by varying the Ge concentration from 10 at.% to 30 at.%, we study the effects of the PCM composition on the physical and electrical properties of sputtered GexSb100−x films. The Ge10Sb90 film assumes a crystal trigonal structure (Sb phase); however, phase separation occurs in the films at higher Ge concentrations (i.e., the Sb phase coexists with the crystalline Ge phase). As the Ge concentration increases, the grain size decreases, and the sheet resistances of both the amorphous and crystalline states increase. An increase in the Ge concentration in these GeSb films results in an increase in the crystallization temperature, activation energy, data retention, and band gap. The current–voltage measurements show that the threshold and RESET currents decrease with increasing Ge concentrations. In addition, we discuss the R–V curve, crystallization speed, and programming window. The results indicate that GeSb films possess favorable physical and electrical characteristics and can be used as PCMs in phase-change memory applications.

Synthesis, theoretical and experimental characterisation of thin film Cu2Sn1-xGexS3 ternary alloys (x = 0 to 1): Homogeneous intermixing of Sn and Ge

Cu2Sn1-xGexS3 is a p-type semiconductor alloy currently investigated for use as an absorber layer in thin film solar cells. The aim of this study is to investigate the properties of this alloy in thin film form in order to establish relationships between group IV composition and structural, vibrational and opto-electronic properties. Seven single phase Cu2Sn1-xGexS3 films are prepared from x = 0 to 1, showing a uniform distribution of Ge and Sn laterally and in depth. The films all show a monoclinic crystal structure. The lattice parameters are extracted using Le Bail refinement and show a linear decrease with increasing Ge content. Using density-functional theory with hybrid functionals, we calculate the Raman active phonon frequencies of Cu2SnS3 and Cu2GeS3. For the alloyed compounds, we use a virtual atom approximation. The shift of the main Raman peak from x = 0 to x = 1 can be explained as being half due to the change in atomic masses and half being due to the different bond strength. The bandgaps of the alloys are extracted from photoluminescence measurements and increase linearly from about 0.90 to 1.56 eV with increasing Ge. The net acceptor density of all films is around 1018 cm−3. These analyses have established that the alloy forms a solid solution over the entire composition range meaning that intentional band gap grading should be possible for future absorber layers. The linear variation of the unit cell parameters and the band gap with group IV content allows composition determination by scattering or optical measurements. Further research is required to reduce the doping density by two orders of magnitude in order to improve the current collection within a solar cell device structure.

A Behavioral Model for High Ge Content in Si/Si1-xGex Multi-Quantum Well Detector

This paper presents a behavioral model for a Si/Si1− x Ge x multi-quantum well (MQW) detector that predicts device characteristics to investigate the effect of increasing Ge content in Si/Si1− x Ge x MQW. The modeling approach in this paper is based on a physical instead of empirical approach, which allows to obtain a predictive behavioral analysis of high Ge content with only a few fitting parameters. The model is used to simulate device transfer characteristics with respect to various amounts of Ge content used for Si1− x Ge x layer in MQW. The simulation results of the proposed model are validated with the experimental data. The simulated and the experimental data are consistent over a wide range of Ge content varied from 30% up to 50%. The primary objective of this paper is to optimize Ge content in the Si/Si1− x Ge x MQW detector to achieve desired thermal sensitivity measured in terms of temperature coefficient of resistance for a potential microbolometer application. This is the first study in the literature to develop such a highly predictive behavioral model of a Ge-enriched Si/Si1− x Ge x MQW. The study also presents the effect of including the carbon delta layers at the Si/Si1− x Ge x heterointerface on the device transfer characteristics. The effect of Ge content on the overall noise is also investigated by the noise characterization of the test devices.

Reduced graphene oxide-germanium quantum dot nanocomposite: electronic, optical and magnetic properties

Graphene provides numerous possibilities for structural modification and functionalization of its carbon backbone. Localized magnetic moments can, as well, be induced in graphene by the formation of structural defects which include vacancies, edges, and adatoms. In this work, graphene was functionalized using germanium atoms, we report the effect of the Ge ad atoms on the structural, electrical, optical and magnetic properties of graphene. Reduced graphene oxide (rGO)-germanium quantum dot nanocomposites of high crystalline quality were synthesized by the microwave-assisted solvothermal reaction. Highly crystalline spherical shaped germanium quantum dots, of diameter ranging between 1.6–9.0 nm, are anchored on the basal planes of rGO. The nanocomposites exhibit high electrical conductivity with a sheet resistance of up to 16 Ω sq−1. The electrical conductivity is observed to increase with the increase in Ge content in the nanocomposites. High defect-induced magnetization is attained in the composites via germanium adatoms. The evolution of the magnetic moments in the nanocomposites and the coercivity showed marked dependence on the Ge quantum dots size and concentration. Quantum confinement effects is evidenced in the UV–vis absorbance spectra and photoluminescence emission spectra of the nanocomposites which show marked size-dependence. The composites manifest strong absorption in the UV region, strong luminescence in the near UV region, and a moderate luminescence in the visible region.

First-principles investigation of the structural, electronic and optical properties of Ge-doped MgSiAs2

We report the results of studies on the structural, electronic and optical properties of MgSi1−xGexAs2(x = 0, 0.25, 0.5, 0.75 and 1) using density functional theory (DFT) based on the full-potential linear augmented plane wave (FP-LAPW) method. To treat the exchange-correlation potential for the total energy calculations, the generalized gradient approximation (WC-GGA) by Wu-Cohen was used. Additionally, the modified Becke Johnson (mBJ) potential approximation, which successfully corrects the band-gap problem, was used for the band structure calculations. The calculated lattice constants and band-gap values for these alloys are in good agreement with the available theoretical and experimental data. A decrease in the band gap is observed with an increasing Ge content. The dielectric function and absorption coefficient are calculated to investigate the optical properties. Electronic and optical properties reveal that these alloys should be very useful for applications in photonics, optoelectronics and optics.

Phase Stabilities and Magnetic Properties of Mn-Deficient and Ge-Substituted Mn3Ga With D022Structure

We have investigated phase stabilities and magnetic properties of the tetragonal D022 phase in Mn-deficient Mn3– x Ga and Ge-substituted Mn3Ga1– y Ge y . A transition from the D022 to L10 phase is observed in the composition range of $x = 0.5$ –0.8 in Mn3– x Ga. On the other hand, the D022 phase is confirmed in the overall composition of Mn3Ga1– y Ge y . The thermal stability of the D022 phase strongly depends on the Ge content compared with the Mn deficiency. Magnetization of Mn3– x Ga is increased by introducing the Mn deficiency, whereas that of Mn3Ga1– y Ge y decreases with increasing Ge content despite a constant number of Mn atoms. This result suggests that the magnitude of magnetic moment of Mn atom in Mn3Ga1– y Ge y is influenced by variations of valence electron and structural properties caused by the Ge substitution.

Kinetics of glass transition of GeySe94-yIn6 (y = 10, 15 and 20) chalcogenide glasses under non-isothermal condition

ABSTRACTKinetics of glass transition of GeySe94-yIn6 (y = 10, 15 & 20) glassy alloys has been studied under non-isothermal condition using Differential Scanning Calorimetery (DSC). The glassy alloys have been prepared by rapid quenching of melt technique. For structure characterization, XRD and EDAX techniques have been used. DSC thermograms have been recorded at heating rates 5, 10, 15 and 20 K/min. from room temperature to 823 K. Lasocka's empirical relation has been used to study the heating rate dependence of glass transition temperature. Activation energy of glass transition, evaluated from Kissinger Peak shift method, increases with increase of Ge content in GeySe94-yIn6 (y = 10, 15 & 20) glassy series.

Formation of a Ge-rich Si1−xGex (x > 0.9) fin epitaxial layer condensed by dry oxidation

We have selectively grown an epitaxial Si0.35Ge0.65 fin layer in a 65 nm oxide trench pattern array and formed a Ge-rich Si1−xGex (x > 0.9) fin layer with condensed Ge using dry oxidation. During oxidation of the SiGe fin structure, we found that the compressive strain of the condensed SiGe layer was increased by about 1.3% while Ge was efficiently condensed due to a two-dimensional oxidation reaction. In this paper, we discussed in detail the diffusion during the two-dimensional condensation reaction as well as the asymmetric biaxial strain of the SiGe fin before and after oxidation using a reciprocal space mapping measurement. The application of dry oxidation on selectively grown SiGe fin layer can be an effective method for increasing hole mobility of SiGe fin with increased Ge content and self-induced compressive strain.

The Impact of Dummy Gate Processing on Si-Cap-Free SiGe Passivation: A Physical Characterization Study on Strained SiGe 25% and 45%

High mobility channel materials like SiGe, Ge and IIIV receive lots of interest in order to enable the continuation of Moore’s path during the upcoming technology nodes. Recently Si-cap-free SiGe passivation with the number of interface states (NIT) down to 2 1011 cm-2 have been demonstrated. [1-3] A clear correlation was established between Ge-content in the SiGe-oxide and NIT. Unfortunately no process information has been provided on how the Ge-oxide-free interlayers were obtained. In a separate study the impact of HF, HCl and SC1 cleaning solution on the SiGe surface and oxide composition was reported. [4] A comparison of SiGe Gate-All-Around (GAA) and FinFET devices using a Si-cap-free SiGe 25% passivation scheme in a replacement metal gate (RMG) integration indicate the device performance is improved by a TMAH (aq) treatment prior to SiGe interlayer formation and high-k deposition. [5] Here the formation of a SiGe wet chemical oxide will be presented. The impact of dummy gate processing on the interlayer composition is reported. Also the impact of a TMAH (aq) treatment prior to chemical oxide formation has been analyzed and will be reported. Blanket strained SiGe 25% and 45% were grown by epitaxy. The SiGe-substrate and -oxide composition were measured by angle-resolved XPS using the Si2p and Ge3d peaks. The Ge3d peak is fitted with three different compounds: elemental Ge, GeO2 and Ge-suboxide. The angle dependence lets us estimate the distribution of the different components with respect to the sample top surface. An concentration increase with increasing angle (relative to the surface normal) indicates the compound is located closer to the sample surface. And reversely a concentration increase with increasing angle indicates the compound is located deeper into the sample. A native oxide was grown on SiGe 25 and 45% by exposing the wafers to the cleanroom air for approx. 1 week. The native oxide was found to be stoichiometric or nearly stoichiometric with a uniform Ge content throughout the oxide for SiGe 25 and 45% respectively. A wet chemical oxide was grown using an ‘imec clean’ [6] having a final O3/HCl (aq) rinse. The wet chemical oxide is Ge-poor compared to the SiGe substrate. No or only a small variation in Ge content of the SiGe-oxide is seen with ARXPS. However the fraction Ge-suboxide decreases with increasing angle, indicating the Ge-suboxide are located deeper within the sample, so closer to the SiGe-oxide/SiGe-substrate interface. The Ge-content of the SiGe-substrate after wet chemical oxidation shows a weak incident-angle-dependence, indicative a limited Ge enrichment of the SiGe substrate towards the SiGe-oxide/-substrate interface. The low Ge content of the SiGe-oxide is attributed to the water solubility of GeO2. The increase in Ge-content towards the SiGe-oxide/-substrate can be (at least partially) attributed to the poor water solubility of Ge-suboxide. The small increase in Ge content of the SiGe substrate can be attributed to the thermodynamically preferred oxidation of Si over Ge. The combined impact of dummy gate deposition, spike anneal and dummy gate removal prior to SiGe interlayer formation was investigated by AR-XPS and SIMS. The temperature used during spike anneal was found to have a significant impact on the Ge-content of the SiGe-oxide formed during an O3-last imec clean. The results will be reported in detail at the conference. The impact of TMAH (aq) on the chemical oxide composition and surface roughness will also be reported. TMAH (aq) was found to improve SiGe device performance. [5] Also the interaction with the subsequent HfO2 deposition will be reported. In summary SiGe is found to behave as a non-linear combination of Si and Ge. In HF-free aqueous solutions, the SiGe oxide composition is a combination of (1) thermodynamically preferred oxidation of Si versus Ge; (2) poor water-solubility of SiO2 and/or its low solubilization rate; and (3) fast dissolution of GeO2 but slow dissolution of Ge-suboxides. [1] CH Lee et al. VLSI 2016. [2] S. Siddiqui et al. presented MRS Spring Meeting 2016. [3] CH Lee et al. IEDM 2016. [4] S.L. Heslop et al. ECS Trans 69 (2015) 287. [5] H. Mertens et al VLSI 2015. [6] M. Meuris et al. Solid State Phenom, July 1995, p. 109. Figure 1

Tunable negative thermal expansion and structural evolution in antiperovskite Mn3Ga1−xGexN (0 ≤ x ≤ 1.0)

AbstractThe negative thermal expansion (NTE) and structural evolution of antiperovskite compounds Mn3Ga1−xGexN (0 ≤ x ≤ 1.0) were systematically investigated. Our results indicate the crystal structure of Mn3Ga1−xGexN changes from cubic (C) to tetragonal (T4) with increasing Ge content by X‐ray diffraction (XRD).The negative thermal expansion from x = 0 (operation‐temperature range ▵T = 20 K) to x = 0.4 (▵T = 60 K) becomes broad and shifts to higher temperature, and then it became positive from x = 0.5 in Mn3Ga1−xGexN. Typically, Mn3Ga0.5Ge0.5N shows low thermal expansion behavior between 300 and 450 K (∆T = 150 K), and thermal expansion coefficient α is estimated to be 2 × 10−6 K−1. Furthermore, variable temperature XRD was measured to reveal the origin of NTE. The cubic I ‐ cubic II phases coexistence (x = 0.2) and cubic I ‐ tetragonal coexistence (x = 0.5, 0.6) was observed at low temperature. The tunable NTE is highly valuable for practical applications in precision devices.

Structural and physical properties of Ge-doped CuCrO 2 delafossite oxide

Abstract Ge-doped CuCrO 2 delafossite semiconductors were synthesized using a conventional solid-state reaction method. The influence of Ge concentration (0–5%) on its microstructural, optical, and magnetic properties were investigated. X-ray diffraction (XRD) analysis results revealed the delafossite structure in all the samples. There is no significant difference in the lattice spacing of CuCr 1- x Ge x O 2 samples with increasing substitution of Ge at the Cr site. This indicated that the Ge entrance into the Cr sublattice in the form of Ge 2+ , and Ge 4+ ions in CuCr 1- x Ge x O 2 ceramics, which is further certified by X-ray photoelectron spectra. The optical properties measured at room temperature by UV–visible spectroscopy showed a weak absorbability in the visible light and near IR regions. The corresponding direct optical band gap was about 3.61 eV, exhibiting transparency in the visible region. The magnetic hysteresis curve measurements showed that the Ge-doped CuCrO 2 samples exhibit paramagnetic behavior at room temperature. However, ferromagnetism is achieved in the Ge-doped CuCrO 2 samples at 50 K. The magnetization of this CuCr 1- x Ge x O 2 delafossite is increased almost linearly with the increasing Ge concentration. This indicated that the combined influence of the number of the M–M pairs, and long-range and short-range interactions of M–M couplings produce a mixed effect on the magnetic properties of CuCrO 2 delafossite oxide. The dielectric measurements clearly revealed the dielectric permittivity of CuCrO 2 strongly inhibited by Ge doping.

Thermoelectric transport properties of Sn1−x Ge x Se (x =0-0.03) prepared by melting synthesis method

P-type Sn1−xGexSe (x=0-0.03) polycrystals were prepared through direct melting synthesis method. The composition and microstructure of the samples were analyzed, and the thermoelectric transport properties were investigated in temperatures ranging from 303 to 773 K. The results indicate that the electrical conductivity decreases as Ge content increases. A significant improvement was found for the Seebeck coefficient. The maximal value of 647 μV/K was achieved at 473 K for the sample of Sn0.97Ge0.03Se. The Hall transport properties result indicates that the carrier concentration decreases with Ge content increasing at room temperature. In addition, the total thermal conductivities (κtot) of all samples decrease with rising temperature.

Realisation of magnetostructural coupling and a large magnetocaloric effect in the MnCoGe1+x system

Magnetic field-induced magnetostructural transformations taking place in MnCoGe-based alloys attract considerable attention due to their associated multi-magnetoresponsive effects. The key to maximising these effects across a wide working temperature range is to increase the magnetisation difference during the transformation and simultaneously sustain the Curie temperatures of the Ni2In and TiNiSi phases. In this work, we achieve the above goals by importing additional Ge atoms into the MnCoGe alloy, as the increase in Ge content sharply decreases the transformation temperature but does not influence the Curie temperatures in the system. As a result, magnetostructural transformation between paramagnetic Ni2In and ferromagnetic TiNiSi phases is realised within a Curie-temperature window of 70K. The magnetostructural transformation can be induced by the magnetic field, bringing about considerable entropy change.

Raman characterization and modelling of Cu2ZnSn1-XGeXS4 single crystals grown using chemical vapor transport

Reported in this paper are the results of investigations aimed at Cu2ZnSn1-XGeXS4 single crystals. A detailed study of Raman spectra at room temperature and 80 K for crystals synthesized in two one-type processes was performed. It has been shown that even insignificant temperature fluctuations during the synthesis can cause changes of elemental composition in these compounds. The analysis of the Raman spectra inherent to the grown samples confirms that they crystallize in the kesterite structure. It has been ascertained that, when the Ge content increases, the Raman spectra of Cu2ZnSn1-XGeXS4 show a two-mode reconstruction of both full-symmetric bands related with sulfur atom vibration in Sn-S4 and Ge-S4 tetrahedra. These experimental bands have been described by theoretical curves calculated within the framework of a bound oscillator model. Based on this model, one can adequately describe the changes both in the band intensity and frequency position for various elemental compositions.

The effect of Germanium addition on mechanical properties& microstructure of Cu-Al-Ni shape memory alloy

This paper aims to study the effect of Ge addition in different percentages (0.3%wt,1%wt, 3%wt) on the micro structure and mechanical properties of Cu-14wt%Al-4.5wt%Ni shape memory alloy which prepared by casting method in vacuum induction furnace. Many tests and inspections such as optical and SEM examinations, DSC Measurement,XRD inspection, compression and Vickers hardness tests were investigated. The results show that there is an increase in the transformation temperatures, shape memory limits and decrease in hardness and increase in Young Modulus Also it was found that the increase of Ge content to 3%wt Ge gave better properties due to the formation of martensitic phase and Ge particles distribution in martensite matrix of SMA.

Optical investigation of thermally evaporated Cu5GexTe95−x thin films

Cu5GexTe95−x (x = 14, 16, 18 and 20) thin films were successfully deposited using thermal evaporation technique. The optical transmittance (T) and reflectance (R) spectra in the wavelength range 250–2500 nm were used for the determination of the optical energy gap and the associated optical constants of the deposited thin films. It was found that, the absorption coefficient (α), refractive index (n) and the extinction coefficient (k) spectra vary with increasing Ge concentration. The indirect optical band gap Eg is found to decrease while the Urbach tail energy increases for different film compositions. The refractive index dispersion data were analysed using the Wemple–DiDomenico single-effective-oscillator model. As a result, the oscillator energy (Eso), dispersion energy (Ed), oscillator strength (Sso), and zero-frequency refractive index (no) were determined. The dependence of the optical constants of Cu5GexTe95−x on the photon energy (hν) at different Ge concentrations is discussed.

Enhancing crystalline silicon solar cell efficiency with SixGe1−x layers

Crystalline silicon (c-Si) solar cell represents a cost effective, environment-friendly, and proven renewable energy resource. Industrially manufacturing of c-Si solar has now matured in terms of efficiency and cost. Continuing cost-effective efficiency enhancement requires transition towards thinner wafers in near term and thin-films in the long term. Successful implementation of either of these alternatives must address intrinsic optical absorption limitation of Si. Bandgap engineering through integration with SixGe1−x layers offers an attractive, inexpensive option. With the help of PC1D software, role of SixGe1−x layers in conventional c-Si solar cells has been intensively investigated in both wafer and thin film configurations by varying Ge concentration, thickness, and placement. In wafer configuration, increase in Ge concentration leads to enhanced absorption through bandgap broadening with an efficiency enhancement of 8% for Ge concentrations of less than 20%. At higher Ge concentrations, despite enhanced optical absorption, efficiency is reduced due to substantial lowering of open-circuit voltage. In 5–25-μm thickness, thin-film solar cell configurations, efficiency gain in excess of 30% is achievable. Therefore, SixGe1−x based thin-film solar cells with an order of magnitude reduction in costly Si material are ideally-suited both in terms of high efficiency and cost. Recent research has demonstrated significant improvement in epitaxially grown SixGe1−x layers on nanostructured Si substrates, thereby enhancing potential of this approach for next generation of c-Si based photovoltaics.

Effects of work hardening rate on formation of nanocrystallized subsurface layer in Cu alloys

The effects of the work hardening rate on the formation of a nanocrystallized subsurface layer by sliding wear for pure Cu and Cu–Ge alloys are investigated. The nanocrystallized subsurface layer is called the wear-induced layer (WIL). The work hardening rates of the Cu–Ge alloys increase with Ge concentration. By sliding wear, the WIL is formed around a worn surface in all the specimens. The thickness of the WIL decreases with increasing Ge concentration. This means that a thinner WIL is formed in a specimen with a higher work hardening rate. The equivalent Hencky strain required to form the WIL is about 5 regardless of the work hardening rate of the specimen. In addition, a larger strain gradient is generated just below the WIL in the specimen with a higher work hardening rate. This decrease in the thickness of the WIL depending on the work hardening rate of the specimen can be explained by the localization of shear deformation around the worn surface.