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Direct bandgap group IV materials could provide intimate integration of lasers, amplifiers, and compact modulators within complementary metal–oxide–semiconductor for smaller, active silicon photonics. Dilute germanium carbides (GeC) with ∼1 at. % C offer a direct bandgap and strong optical emission, but energetic carbon sources such as plasmas and e-beam evaporation produce defective materials. In this work, we used CBr4 as a low-damage source of carbon in molecular beam epitaxy of tin-free GeC, with smooth surfaces and narrow x-ray diffraction peaks. Raman spectroscopy showed substitutional incorporation of C and no detectable sp2 bonding from amorphous or graphitic carbon, even without surfactants. Photoluminescence shows strong emission compared with Ge. [ABSTRACT FROM AUTHOR]

Direct bandgap group IV materials could provide intimate integration of lasers, amplifiers, and compact modulators within complementary metal–oxide–semiconductor for smaller, active silicon photonics. Dilute germanium carbides (GeC) with ∼1 at. % C offer a direct bandgap and strong optical emission, but energetic carbon sources such as plasmas and e-beam evaporation produce defective materials. In this work, we used CBr4 as a low-damage source of carbon in molecular beam epitaxy of tin-free GeC, with smooth surfaces and narrow x-ray diffraction peaks. Raman spectroscopy showed substitutional incorporation of C and no detectable sp2 bonding from amorphous or graphitic carbon, even without surfactants. Photoluminescence shows strong emission compared with Ge. [ABSTRACT FROM AUTHOR]

Si1 –xGex alloy nanoparticles with controlled composition have been obtained by nanosecond laser ablation of silicon–germanium targets in isopropanol. The synthesized product exhibits a polycrystalline structure and a unimodal size distribution with a predominant content of microparticles and retains the stoichiometry of the composition of the targets used for the synthesis. Nanothermometry with the detection and analysis of a Raman signal from single alloy nanoparticles with a size of ~200 nm demonstrates a threefold increase (in comparison with nanoparticles of pure silicon) in the heating efficiency of a nanomaterial with the composition Si0.45Ge0.55 by 785-nm laser radiation falling into the first "transparency window" of biological tissues. Stimulated by continuous infrared radiation, the diffusion of silicon atoms to the surface (when heated to 650 K) and their oxidation lead to the gradual transformation of alloy nanoparticles into germanium clusters encapsulated in a SiOx matrix. [ABSTRACT FROM AUTHOR]

[Display omitted] Micro-sized alloy type germanium (Ge) anodes possess appealing properties for next-generation lithium ions batteries, such as desirable capacity, easy accessibility and greater tap density. Nevertheless, volume expansion accompanied by severe pulverization and continuous growth of solid electrolyte interlayer (SEI) still represent fundamental obstacles to their practical applications. Herein, we propose a fresh strategy of constructing robust bond linkage between boron-based coating layer and lithiated polyacrylic acid (PAALi) binder to circumvent the pulverization problems of Ge anodes. Facile pyrolysis of boric acid can introduce an amorphous boron oxide interphase on Ge microparticles (noted as Ge@B 2 O 3). Then in situ crosslinking reaction between B 2 O 3 and PAALi via B O C bond linkage constructs a robust Ge anode (Ge@B-PAALi), which is proved by FTIR and Raman characterizations. Post morphological and compositional investigations reveal the minimized pulverization and a thinner SEI composition. The robust bond linkage strategy endows Ge anode with ultra-stable cycling properties of 1053.8 mAh/g after 500 cycles at 1 A/g vs. 500.7 mAh/g for Ge@PAALi and 372.7 mAh/g for Ge@B 2 O 3 , respectively. The proposed bond linkage strategy via artificial coating layer and functional binders unlocks huge potential of alloys and other anodes for next-generation battery applications. [ABSTRACT FROM AUTHOR]

The ternary alloy of germanium, antimony, and tellurium (GST) is widely used as a material for phase-change memories. In particular, the stoichiometric compound Ge 2 Sb 2 Te 5 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. [ABSTRACT FROM AUTHOR]

The microstructure of Ti-6Al-4V titanium alloy produced by laser additive manufacturing is generally relatively coarse, so its mechanical properties have not yet achieved satisfactory results. After adding germanium element to titanium alloy, second phase particles can be formed, at the same time, due to strong bonding force between Ti and Ge atoms, there also have other strengthening effects that need to be revealed. Therefore, the effect of Ge addition on the microstructure and mechanical properties of additive manufactured Ti-6Al-4V alloy was studied in detail in this paper, which can provide more reference for optimizing the performance of titanium alloy manufactured with additives manufacturing. The pure Ge powder was ball milled with Ti-6Al-4V powder in several different proportions, and bulk samples were prepared by laser deposition manufacturing (LDM) with the mixed powder. The Germanium alloyed Ti-6Al-4V alloy's tensile strength and plasticity at room temperature increased about 25% and 10%, respectively, compared with LDMed Ti-6Al-4V alloy without Ge. According to the results of TEM and EDS, Ti and Ge reacted to form granular second phase Ti5Ge3, which distributes along the primary β grain boundary inhibit the growth of columnar crystals. Part of Ge solutes into α phase. Both microstructure refinement and solid solution are very effective in impeding the moving of dislocation, so that the Germanium alloyed LDMed Ti-6Al-4V alloy showed excellent tensile property at room temperature. [ABSTRACT FROM AUTHOR]

The last missing piece of the puzzle for the full functionalization of group IV optoelectronic devices is a direct bandgap semiconductor made by CMOS compatible technology. Here, we report on the fabrication of GeSn alloys with Sn concentrations up to 4.5% using ion implantation followed by millisecond-range explosive solid phase epitaxy. The n-type single crystalline GeSn alloys are realized by co-implantation of Sn and P into Ge. Both the activation of P and the formation of GeSn are performed during a single-step flash lamp annealing for 3 ms. The bandgap engineering in GeSn as a function of the doping level and Sn concentration is theoretically predicted by density functional theory and experimentally verified using ellipsometric spectroscopy. We demonstrate that both the diffusion and the segregation of Sn and P atoms in Ge are fully suppressed by millisecond-range nonequilibrium thermal processing. [ABSTRACT FROM AUTHOR]

The germanium-tin (Ge-Sn) alloy has been considered a candidate for applications in Short Wave Infrared optical electronics, because it has the property of transforming pure germanium (Ge), typically an indirect bandgap material, into a direct bandgap material. In this paper, the effects of volumetric and potential energy changes are utilized to calculate how the band structure of the Ge-Sn alloy changes with respect to the fraction of tin (Sn). The results indicate that a transition occurs for a Sn fraction ranging from 5.81% to 8.75% with the alloy lattice-constant bowing parameter that ranges from 0.3 Å to 0.0 Å. [ABSTRACT FROM AUTHOR]

The possibility of partial substitution of Si for Ge in the structure of Bi2GeO5 during synthesis from the melt and the effect of the substitution on the structure of the synthesized material have been studied. The microstructure of the synthesized compounds after their complete decomposition has been investigated. Using the phase powder X-ray diffraction- and optical microscopy methods, it has been found that metastable phases of bismuth silicate and germanate with structures of the Aurivillius type form a continuous series of solid solutions. It is shown that a mixed structure composed of large Bi4Si(Ge)3O12 crystals and the Bi12Si(Ge)O20 + Bi4Si(Ge)3O12 point eutectic is obtained after the decomposition of compounds of the Bi2SiO5–Bi2GeO5 quasi-binary system, regardless of the percentage of substitution of Si for Ge. Upon slow heating up to annealing temperatures (at a rate of 13.5°C/min), a structure of decomposition that is more finely dispersed and uniform than the structure obtained upon rapid heating (when charg the material into an already preheated furnace), which is more coarsely grained and inhomogeneous. Moreover, regions with a large structure similar to a dendritic one can appear in the material when the contents of silicon and germanium oxides in the alloy are close to each other (20/30–30/20 mol %). Such regions differ slightly in chemical composition from the surrounding material and appear during both slow and rapid heating of the material to annealing temperatures. [ABSTRACT FROM AUTHOR]

P type silicon germanium alloy thermoelectric semiconductor materials doped with B (contents of 0. 5at. % 1 at %, 1. 5at %, 2at. %) were prepared by electromagnetic fusion method. According to the phase analysis and microscopic morphology analysis of the samples the conditions for the alloying of silicon germanium by electromagnetic fusion method were determined, and the thermoelectric properties of the prepared P type silicon germanium alloy thermoelectric semiconductor samples at 200 to 800 °C were tested. The results show that electromagnetic stirring fusion holding for 120 min and using the secondary cooling crystallization method can complete the alloying of silicon germanium and can reduce the precipitation of germanium during the cooling crystallization process and improve the uniformity of the sample; the doped B prepared by the electromagnetic fusion method. The thermoelectric figure of merit of the P type silicon germanium alloy thermoelectric semiconductor with a content of 1. 5 at % can reach 0. 43 at 800 °C. The method has the advantages of simple preparation process-short preparation time and strong repeatability and provides a new idea for the preparation of silicon germanium thermoelectric materials. [ABSTRACT FROM AUTHOR]

A modified equation of state and a thermodynamically equilibrium model are used to numerically simulate the thermodynamic parameters of shock-wave loading of germanium in its pure form, as well as alloys with germanium as a component. The parameters of the equations of state for two phases of germanium are determined. The thermodynamic parameters are modeled for these Ge I and Ge II phases in the pressure range from 1 to 400 GPa. The shock adiabats for both phases are plotted, and the heat capacity values along the normal isobars and isochores and the entropy values for germanium as a function of temperature were calculated. The simulation results are compared with the results of other authors (both calculations and experiments). [ABSTRACT FROM AUTHOR]

• Thermodynamic parameters of the GeTe-rich germanium-bismuth tellurides were studied using an electromotive force (EMF) method. • Solid-phase equilibria diagram of the GeTe-Bi 2 Te 3 -Te system were constructed. • The standard thermodynamic functions of formation and standard entropies of Ge 2 Bi 2 Te 5 , Ge 3 Bi 2 Te 6 , and Ge 4 Bi 2 Te 7 ternary compounds were calculated. A set of self-consistent thermodynamic parameters of the GeTe-rich germanium-bismuth tellurides were determined using an electromotive force (EMF) method with a glycerol electrolyte in a temperature range from 300 to 450 K. The solid-phase equilibrium diagram of the GeTe-Bi 2 Te 3 -Te system at 400 K was constructed using X-ray diffraction (XRD) and scanning electron miscroscope (SEM) techniques of synthesized electrode alloys, as well as available literature data. It is found that all telluride phases in GeTe-Bi 2 Te 3 pseudo-binary section have a tie-line connection with elemental tellurium. The relative partial thermodynamic functions of GeTe in alloys were calculated using data from EMF measurements of concentration cells relative to the GeTe electrode. These findings together with the corresponding thermodynamic functions of GeTe and Bi 2 Te 3 were used to calculate the relative partial molar functions of germanium in alloys, and also the standard thermodynamic functions of formation and standard entropies of the ternary compounds, namely Ge 2 Bi 2 Te 5 , Ge 3 Bi 2 Te 6 and Ge 4 Bi 2 Te 7. [ABSTRACT FROM AUTHOR]

We fabricated nanocrystalline Ge films using radio-frequency (RF) magnetron plasma sputtering deposition under a high Ar-gas pressure. The Ge nanograins changed from amorphous to crystalline when the distance between the Ge sputtering target and the substrate was decreased to 5 mm and the RF input power was 11.8 W/cm2 (60 W), where the deposition rate was as high as 660 nm/min. In addition, the size of the nanocrystalline grains increased from 100 to 307 nm when the RF input power for plasma production was increased from 11.8 W/cm2 (60 W) to 17.7 W/cm2 (90 W). In the developed narrow-gap plasma process at sub-Torr pressures, nanocrystalline Ge films were successfully fabricated on Cu substrates at low temperatures, without the substrate being heated. However, when annealing was conducted under an N2 atmosphere, which is the conventional method to induce solid-phase crystallization, the amorphous Ge layer on a Cu substrate changed to a Cu3Ge crystal layer through interdiffusion of Ge and Cu atoms at 400–500 °C.

We consider SicGe1–c graded systems of length L = 3 mm and L = 100 nm, under the action of an electric field E, and crossed by an electrical current i, the two sides of which are kept at two different temperatures Th and Tc. The dependence on composition and temperature of the thermal conductivity is analyzed. We evaluate the thermal conductivity in correspondence of the constant temperatures T = 300 K, T = 400 K, and T = 500 K and investigate the thermoelectric efficiency of the system as a function of the stoichiometric variable c and of the effective temperature gradient T h − T c L . For each temperature, we calculate the values of c in the interval [0, 1] which realize the optimal efficiency of the thermoelectric energy conversion. The corresponding values of the thermal conductivity are determined as well. For L = 3 mm, we find that the best efficiency of thermoelectric energy conversion is achieved at T = 500 K, c = 0.325568, and λ = 7.3444 Wm−1 K−1. For L = 100 nm, we obtain the best efficiency at T = 500 K, c = 0.613937, and λ = 0.1510 Wm−1 K−1. [ABSTRACT FROM AUTHOR]

A method for reduction of threading dislocation density (TDD) in lattice-mismatched heteroepitaxy is proposed, and the reduction is experimentally verified for Ge on Si. Flat-top epitaxial layers are formed through coalescences of non-planar selectively grown epitaxial layers, and enable the TDD reduction in terms of image force. Numerical calculations and experiments for Ge on Si verify the TDD reduction by this method. The method should be applicable to not only Ge on Si but also other lattice-mismatched heteroepitaxy such as III-V on Si. [ABSTRACT FROM AUTHOR]

Hexagonal Si and Ge with a lonsdaleite crystal structure are allotropes of silicon and germanium that have recently been synthesized. These materials as well as their alloys are promising candidates for novel applications in optoelectronics. In this paper, we systematically study the phonon transport and thermal conductivity of hexagonal Si, Ge, and their alloys by using the first-principle-based Peierls-Boltzmann transport equation approach. Both three-phonon and four-phonon scatterings are taken into account in the calculations as the phonon scattering mechanisms. The thermal conductivity anisotropy of these materials is identified. While the thermal conductivity parallel to the hexagonal plane for hexagonal Si and Ge is found to be larger than that perpendicular to the hexagonal plane, alloying effectively tunes the thermal conductivity anisotropy by suppressing the thermal conductivity contributions from the middle-frequency phonons. The importance of four-phonon scatterings is assessed by comparing the results with the calculations without including four-phonon scatterings. We find that four-phonon scatterings cannot be ignored in hexagonal Si and Ge as the thermal conductivity would be overestimated by around 10% (40%) at 300 K (900) K. In addition, the phonon mean free path distribution of hexagonal Si, Ge, and their alloys is also discussed. [ABSTRACT FROM AUTHOR]

Regularities of composition changes of silicon/germanium alloy thin films formed on a single-crystalline silicon substrate by electrochemical deposition of germanium into a porous silicon matrix with subsequent rapid thermal annealing (RTA) at temperatures of 750–950°C are studied. An analysis of the samples by Raman spectroscopy showed that an increase of the RTA temperature leads to a decrease in the germanium concentration in the formed film. A decrease of the RTA duration at a given temperature makes it possible to obtain films with a higher germanium concentration and to control the composition of thin silicon/germanium alloy films formed by changing the RTA temperature and duration. The obtained results on controlling the composition of silicon/germanium alloy films can be used to create functional electronic devices, thermoelectric power converters, and optoelectronic devices. [ABSTRACT FROM AUTHOR]

The HfxZryO2 with high Zr content is demonstrated to form the anti-ferroelectric tetragonal phase (AFE t-phase). The peak dielectric constant (47) of Hf0.2Zr0.8O2 is achieved. By taking advantage of the high dielectric constant, the Hf0.2Zr0.8O2 is used in the gate stack on the high mobility Ge0.98Si0.02 channel to significantly enhance the drive current. Stacked two Ge0.98Si0.02 gate-all-around nanowires can have high ION per perimeter of $740~\mu \text{A}/\mu $ m at $\mathrm{V}_{\mathrm{OV}}= \mathrm{V}_{\mathrm{DS}}= 0.5\text{V}$. The thermal budget is as low as 450 °C. [ABSTRACT FROM AUTHOR]

Free energy functionals of the Ginzburg--Landau type lie at the heart of a broad class of continuum dynamical models, such as the Cahn--Hilliard and Swift--Hohenberg equations. Despite the wide use of such models, the assumptions embodied in the free energy functionals frequently either are poorly justified or lead to physically opaque parameters. Here, we introduce a mathematically rigorous pathway for constructing free energy functionals that generalizes beyond the constraints of Ginzburg--Landau gradient expansions.We show that the formalism unifies existing free energetic descriptions under a single umbrella by establishing the criteria under which the generalized free energy reduces to gradient-based representations. Consequently, we derive a precise physical interpretation of the gradient energy parameter in the Cahn--Hilliard model as the product of an interaction length scale and the free energy curvature. The practical impact of our approach is demonstrated using both a model free energy function and the silicon--germanium alloy system. [ABSTRACT FROM AUTHOR]

We use equilibrium molecular dynamics simulations to determine the relative role of compositional and structural disorder in a phononic thermal conductivity reduction by studying three 50-50 SiGe alloy structures: ordered alloys, disordered alloys, and amorphous alloys, as well as pure amorphous Si and Ge structures for reference. While both types of disorders significantly reduce thermal conductivity, structural disorder is much more effective to this aim. The examination of phonon lifetimes in disordered alloys shows high values in a low frequency regime governed by Umklapp scattering that are reduced rapidly with increasing frequency following Rayleigh scattering behavior. The local properties analysis reveals that the structural disorder leads to elastic heterogeneities that are significantly larger than density heterogeneities, which is likely the key reason for amorphous semiconductor alloys having lower thermal conductivity than disordered alloys. Temperature dependence of thermal conductivity indicates the importance of propagating phonons and associated Umklapp scattering in SiGe alloy structures. Interestingly, longitudinal modes in amorphous and disordered alloys exhibit similar lifetimes, while transverse modes lifetimes show significant differences and are more temperature dependent. [ABSTRACT FROM AUTHOR]

Crystalline Ge and Si1-xGex alloys (x = 0.83, 0.77) of (100) orientation were implanted with 140 keV Ge- ions at fluences between 5 x 1015 to 3 x 1017 ions/cm², and at temperatures between 23 ²C and 200 ²C. The energy deposition of the ions leads to the formation of porous structures consisting of columnar pores separated by narrow sidewalls. Their sizes were characterized with transmission electron microscopy, scanning electron microscopy, and small angle x-ray scattering. We show that the pore radius does not depend significantly on the ion fluence above 5 x 1015 ions/cm², i.e., when the pores have already developed, yet the pore depth increases from 31 to 516 nm with increasing fluence. The sidewall thickness increases slightly with increasing Si content, while both the pore radius and the sidewall thickness increase at elevated implantation temperatures. [ABSTRACT FROM AUTHOR]

We test a presumed ability behind the phenomenological percolation scheme used for the basic description of the multi-mode Raman spectra of mixed crystals at one dimension along the linear chain approximation, to determine, via the Raman intensities, the nature of the atom substitution, as to whether this is random or due to local clustering/anticlustering. For doing so, we focus on the model percolation-type GeySi1-y system characterized by six oscillators {1×(Ge-Ge),3×(Ge-Si),2×(Si-Si)} and place the study around the critical compositions y ~ (0.16, 0.71, and 0.84) corresponding to nearly matching of intensities between the like Raman modes from a given multiplet (Ge-Si triplet or Si-Si doublet). The interplay between the GeySi1-y Raman intensities predicted by the percolation scheme depending on a suitable order parameter k of local clustering/anticlustering is found to be consistent with ab initio calculations of the GeySi1-y Raman spectra done with the Ab Initio Modeling PROgram code using large (64-, 216-, and 512-atoms) disordered cubic supercells matching the required (y,k) values. The actual "percolation vs. ab initio" comparative insight at moderate/dilute-(Ge,Si) limits, with an emphasis on the k-induced intra-bond transfer of oscillator strength, extends a pioneering one earlier achieved at an intermediate composition (y ~ 0.50) by using small (32-atom) supercells [O. Pagès et al., J. Appl. Phys. 114, 033513 (2013)], mainly concerned with the inter-bond transfer of oscillator strength, providing altogether a complete picture. [ABSTRACT FROM AUTHOR]

This study examines the electrical and dielectric characteristics of magnetic GeMn nanocrystals integrated into a metal-insulator-semiconductor (MOS) configuration for optoelectronic applications. The nanocrystals were produced by solid-state dewetting of an amorphous GeMn layer deposited by MBE on SiO 2 /Si. The nanocrystals exhibit a well-defined hemispheric shape, high homogeneity, and with a Curie temperature higher than that of the ambient temperature. Characterizations by transmission electron microscopy (TEM) coupled with energy-dispersive X-ray spectroscopy (EDS) revealed the crystallinity of the nanocrystals and optimal incorporation of manganese in the nanocrystals, eliminating the usual diffusion or segregation anomalies observed during growth of GeMn alloy on silicon or germanium. Electrical and dielectric tests conducted via current-voltage and impedance spectroscopies on these structures confirmed the integrity of the oxide layer surrounding the GeMn nanocrystals from defects associated with the manganese. In addition, these measurements validated the proper functioning of the MOS structure as a MOS-type Schottky diode. The in-depth analysis of dielectric parameters, such as permittivity (ε), tangent δ , and electric modulus (M) as a function of frequency and bias voltage, revealed no anomalies, thus reinforcing the high quality of the MOS structure enclosing the GeMn nanocrystals. These results mark a significant advance in the growth and integration of magnetic semiconductor nanostructures for optoelectronic applications, paving the way for promising technological developments. • Manganese-doped germanium nanocrystals (GeMn NCs), produced by MBE via a solid-state dewetting process, are successfully integrated into MOS capacitors for optoelectronic applications. • The electrical study focused on the transport mechanisms present in MOS capacitors integrating GeMn NCs, highlighting the Schottky diode metal-insulator-semiconductor. • Impedance spectroscopy was used to conduct the study on the interface state density and the impact of GeMn nanocrystals on the dielectric properties of the MOS structure containing GeMn nanocrystals. The findings unequivocally indicate the absence of any anomalies associated with manganese doping, affirming the exceptional quality of the GeMn nanocrystals. [ABSTRACT FROM AUTHOR]

A novel TreeFET architecture as a combination of stacked nanosheets and additional fin interbridges between nanosheets can enhance ION per footprint. The straight sidewalls of interbridges requires {110} sidewalls, which can be fabricated using n+ Ge/Ge0.95Si0.05/Ge epitaxial layers with co-optimization of wet etching. The TreeFET with {110} interbridges has ION per footprint of $870~\mu \text{A}/\mu \text{m}$ at VOV=VDS=0.5V (2.1X of the referenced 3 stacked nanosheets). To minimize the impurity scattering in the interbridges, the 400 °C annealing is used to drive phosphorus in interbridges into the nanosheets, while the low source/drain resistance is still maintained. The increasing ION down to 77 K indicates that the phonon scattering dominates, and the impurity scattering is minimized in the interbridge channels. [ABSTRACT FROM AUTHOR]

We report the design and fabrication of a high-speed GeSn normal-incidence p-i-n photodetector. To realize high-speed detection in all telecommunication bands, we optimize the Sn content in the absorption layer, the absorption-layer thickness, and the device size. The responsivity of the 18-μm-diameter device at 1550 nm reaches 0.32 A/W with an extended cutoff wavelength of 1700 nm and a 3-dB bandwidth as high as 28 GHz under −3 V bias, clear open eye diagrams are also obtained under zero bias at 1630 nm. All the results indicate that the device has a significant potential for applications in Si-based optical telecommunication in all telecommunication bands.

The eight stacked Ge0.75Si0.25 nanosheets, the seven stacked Ge0.95Si0.05 nanowires, and the six stacked Ge0.95Si0.05 nanowires without parasitic channels are demonstrated. These highly stacked channels are made from 18 epilayers consisting of a Ge buffer, nine heavily P-doped Ge sacrificial layers, and eight GeSi channel layers with the low growth temperature (350 °C and 375 °C) to ensure the entire epilayers metastable without dislocations in the channels. The isotropic wet etching by H2O2 and NH4OH + H2O2 is used for the channel release and the removal of the parasitic channels, respectively. The delicate interplay between epilayer design and wet etching is implemented to fabricate the highly stacked GeSi channels. High inter-channel uniformity of the eight stacked Ge0.75Si0.25 nanosheets is obtained due to the superior etching selectivity. High ${I}_{\mathrm{\scriptscriptstyle ON}}$ per stack and per footprint of the seven stacked Ge0.95Si0.05 nanowires and the six stacked Ge0.95Si0.05 nanowires without parasitic channels are achieved due to the high mobility ${L}_{4}$ valleys and nanowire conduction. The reduced subthreshold slope (SS) and improved ${I}_{\mathrm{\scriptscriptstyle ON}} / {I}_{\mathrm{\scriptscriptstyle OFF}}$ are obtained by parasitic channel removal. The record ${I}_{\mathrm{\scriptscriptstyle ON}}$ of $120~\boldsymbol \mu \text{A}$ per stack ($4600~\boldsymbol \mu \text{A} / \boldsymbol \mu \text{m}$ per channel footprint) at ${V}_{\mathrm{\scriptscriptstyle OV}} = {V}_{\mathrm{\scriptscriptstyle DS}} = 0.5$ V is reached among reported Ge/GeSi 3-D nFETs. [ABSTRACT FROM AUTHOR]

The absorption coefficient and refractive index of Ge1-xSnx alloys (x from 0% to 10%) were characterized for the wavelength range from 1500 to 2500 nm via spectroscopic ellipsometry at room temperature. By applying physical models to fit the obtained data, two empirical formulae with extracted constants and coefficients were developed: (1) Absorption coefficient. The absorption regarding Urbach tail, indirect and direct bandgap transitions were comprehensively taken into account; (2) refractive index. The Sellmeier coefficients associated with dispersion relationship were extracted. In these formulae, the Sn composition and strain percentage were the input parameters, by inputting which the spectral absorption coefficient and spectral refractive index can be obtained. Since the absorption coefficient is key information to determine the performance of the photodetectors including operation wavelength range, responsivity, and specific detectivity, and the refractive index is very useful for the design of the anti-reflection coating for photodetectors and the layer structure for waveguides, the developed formulae could simplify the optoelectronic device design process due to their parameter-based expressions. [ABSTRACT FROM AUTHOR]

Pseudomorphic GeSn layers with Sn atomic percentages between 4.5% and 11.3% were grown by chemical vapor deposition using digermane and SnCl4 precursors on Ge virtual substrates grown on Si. The layers were characterized by x-ray diffraction rocking curves and reciprocal space maps. Photoconductive devices were fabricated, and the dark current was found to increase with Sn concentration. The responsivity of the photoconductors was measured at a wavelength of 1.55 µm using calibrated laser illumination at room temperature and a maximum value of 2.7mA/W was measured for a 4.5% Sn device. Moreover, the responsivity for higher Sn concentration was found to increase with decreasing temperature. Spectral photoconductivity was measured using Fourier transform infrared spectroscopy. The photoconductive absorption edge continually increased in wavelength with increasing tin percentage, out to approximately 2.4 µm for an 11.3% Sn device. The direct band gap was extracted using Tauc plots and was fit to a bandgap model accounting for layer strain and Sn concentration. This direct bandgap was attributed to absorption from the heavy-hole band to the conduction band. Higher energy absorption was also observed, which was thought to be likely from absorption in the light-hole band. The band gaps for these alloys were plotted as a function of temperature. These experiments show the promise of GeSn alloys for CMOS compatible short wave infrared detectors. [ABSTRACT FROM AUTHOR]

Hydrogenated amorphous silicon germanium alloy (a‐Si1−xGex:H) films are prepared by plasma enhanced chemical vapor deposition (PECVD) and characterized by in situ real time spectroscopic ellipsometry (RTSE). From complex dielectric function spectra extracted, the broadening width energy (Γ) of the primary absorption feature centered near 3.7 eV is quantified using the Cody–Lorentz oscillator model. Mean free path length of photoelectronic excitations is calculated from Γ based on reasonable estimates for speed of electron–hole photoexcitations. A model is applied with excited state lifetime assumed to be limited by scattering from network disorder and provides a relative measure of short‐range order. The simple model applied is an extension of that widely used to characterize broadening of optical transitions in polycrystalline semiconductors. Decreases in mean free path of up to ∼30% occur with germanium. Relative increases in mean free path with increased hydrogen during PECVD a‐Si:H, a‐Si0.73Ge0.27:H, and a‐Si0.60Ge0.40:H occur from ∼5% to ∼8% and with hydrogen plasma treatment of a‐Si:H by ∼6%. Mean free path changes are tracked with thickness to provide short range order evolution and the effect of the underlying material. Mean free path of photoexcitations in electronic quality a‐Si1−xGex:H is estimated at ∼3.5 Å, on the same order as interatomic spacing. [ABSTRACT FROM AUTHOR]

A coupled diffusion and segregation model was derived, where the contributions from diffusion and segregation to dopant flux are explicitly shown. The model is generic to coupled diffusion and segregation in inhomogeneous alloys, and provides a new approach in segregation coefficient extraction, which is especially helpful for heterostructures with lattice mismatch strains. Experiments of coupled P diffusion and segregation were performed with graded SiGe layers for Ge molar fractions up to 0.18, which are relevant to pnp SiGe heterojunction bipolar transistors. The model was shown to describe both diffusion and segregation behavior well. The diffusion-segregation model for P in SiGe alloys was calibrated and Eseg = 0:5 eV is suggested for the temperature range from 800 °C to 950 °C. [ABSTRACT FROM AUTHOR]

We report the thermal conductivity of amorphous SixGe1-x compound calculated versus composition and temperature. The result sets the minimum value of thermal conductivity which is achievable by nanostructuring. We employed molecular dynamics with Tersoff's potential for the calculations. It was found that, contrary to the crystalline SixGe1-x, the thermal conductivity of amorphous phase is a weak function of the material composition. For the most popular composition Si0.8Ge0.2, the thermal conductivity of the amorphous phase is less than 1W m-1 K-1 with small reduction as the temperature increases from 300K to 1400 K. The thermal conductivity of amorphous SixGe1-x for any value of x is approximately an order of magnitude smaller than the minimum thermal conductivity of crystalline SixGe1-x alloy, which occurs near x=0.5. It is known that alloying with germanium is more efficient than nanostructuring to reduce the thermal conductivity of silicon; however, it was found that the amorphization process is even more effective than alloying for that purpose. It was also shown that the reduction of the thermal conductivity of silicon due to alloying with germanium is more efficient in crystalline phase than in amorphous phase. [ABSTRACT FROM AUTHOR]

We have computed phonon scattering rates and density of states in silicon germanium alloys using Green's function calculations and density functional theory. This method contrasts with the virtual crystal approximation (VCA) used in conjunction with Fermi's golden rule, which cannot capture resonance states occurring through the interaction of substitutional impurities with the host lattice. These resonances are demonstrated by density of states and scattering rate calculations in the dilute limit and show broadening as the concentration increases. Although these deviations become significant from the VCA at high frequencies, the relaxation times obtained for these phonon modes are small in both the full scattering theory and the VCA, resulting in their negligible contribution to thermal transport. [ABSTRACT FROM AUTHOR]

The thermodynamic stability of germanium tin alloys is investigated across the composition range by applying density functional theory together with the cluster expansion formalism (CE). It is known that GeSn alloys are immiscible and that non-equilibrium growth techniques are required to produce metastable films and nanostructures. Insight into the driving forces behind component segregation is gained by investigating the equilibrium thermodynamics of GeSn systems. The alloy free energy of mixing is computed by combining enthalpies from the CE with entropy terms for configurational and vibrational degrees of freedom. Volume deformations due to the large mismatch in ionic radii are readily found to be the key driving force for immiscibility at all temperatures of relevance. This leads to a study of epitaxial stabilisation by employing latticed matched substrates to favour growth of alloys with fractional compositions of x = 0, approximately x = 0.5 and x = 1. The reduction in the free energy of mixing due to epitaxial strain in thin films is quantified for each substrate leading to indicators for growth of kinetically stable films. [ABSTRACT FROM AUTHOR]

Among the main characteristics of silver and its alloys, tarnish resistance as well as surface brightness is essential. Alloying these materials with germanium has been shown to have considerable potential in providing tarnish protection. However, studies regarding the electrodeposited silver-germanium (Ag–Ge) alloy coatings are limited. The main objective of this study is to investigate the electrodeposition process of Ag-Ge alloy coatings with different Ge contents. In this regard, co-electrodeposition of Ag and Ge as an alloy coating was performed on pure copper substrates from a cyanide-based electrolyte. The effect of Ge incorporation on alloy composition, surface morphology, topography, texture, crystalline structure and cathodic efficiency of the obtained electrodeposits was investigated. Also corrosion properties of coatings were perused by polarization curves. Evaluation of the coatings was performed using different characterization techniques including XPS, SEM, FESEM, EDS, XRD, AFM, ICP, GIXRD, XRF, FTIR and electrochemical analysis. Results indicated that the optimum content of Ge in the coating was found to be 6 wt% regarding dense and uniform microstructure along with the best corrosion resistance. In addition, the X-ray diffraction patterns exhibited a shift in lattice parameter of Ag that was attributed to the Ag-Ge biphasic alloy formation. Moreover, the surface studies revealed a morphological transformation from nodular to cauliflower-like by increasing the Ge content of coating. The obtained polarization curves represent a remarkable decrease in Ag-6Ge alloy corrosion current density, about 20 times compared to Ag-0.5Ge and about 6 to pure silver. Discrepancies in characteristics between the Ag-Ge and pure Ag coatings were addressed and discussed. [ABSTRACT FROM AUTHOR]

We report the design and fabrication of a high-speed GeSn normal-incidence p-i-n photodetector. To realize high-speed detection in all telecommunication bands, we optimize the Sn content in the absorption layer, the absorption-layer thickness, and the device size. The responsivity of the 18-μm-diameter device at 1550 nm reaches 0.32 A/W with an extended cutoff wavelength of 1700 nm and a 3-dB bandwidth as high as 28 GHz under −3 V bias, clear open eye diagrams are also obtained under zero bias at 1630 nm. All the results indicate that the device has a significant potential for applications in Si-based optical telecommunication in all telecommunication bands. [ABSTRACT FROM AUTHOR]

We systematically study the heteroepitaxy of SiGe alloys on Ge virtual substrates in order to understand strain relaxation processes and maximize the tensile strain in the SiGe layer. The degree of relaxation is measured by high-resolution x-ray diffraction, and surface morphology is characterized by atomic force microscopy. The results are analyzed in terms of a numerical model, which considers dislocation nucleation, multiplication, thermally activated glide, and straindependent blocking. Relaxation is found to be sensitive to growth rate and substrate temperature as well as epilayer misfit and thickness, and growth parameters are found which allow a SiGe film with over 4 GPa of tensile stress to be obtained. [ABSTRACT FROM AUTHOR]

Spectroscopic ellipsometry was used to investigate the optical response of pseudomorphic Ge1–xSnx (0≤x≤0.17) alloys grown directly on Ge (100) by molecular beam epitaxy. A detailed compositional study of amplitudes, broadenings, energies, and phase angles associated with critical points E1, E1+Δ1, E0', and E2 of GeSn alloys was carried out using a derivative analysis. The results can be understood in terms of the electronic bandstructure of Ge or relaxed GeSn alloys with the following differences. First, broadening parameters in pseudomorphic alloys are found to have lower values compared to relaxed alloys indicating lower dislocation density in our pseudomorphic alloys relative to relaxed alloys. Second, the amplitudes of E1 and E1+Δ1 are enhanced and reduced, respectively, with respect to relaxed GeSn alloys, and the trends are captured using the k.p method as a biaxial stress induced effect. Third, phase angles are lower than Ge for all the critical points suggesting reduction of excitonic effects in GeSn with respect to Ge. [ABSTRACT FROM AUTHOR]

Integrated silicon nanophotonics has rapidly established itself as intriguing research field, whose outlets impact numerous facets of daily life. Indeed, nanophotonics has propelled many advances in optoelectronics, information and communication technologies, sensing and energy, to name a few. Silicon nanophotonics aims to deliver compact and high-performance components based on semiconductor chips leveraging mature fabrication routines already developed within the modern microelectronics. However, the silicon indirect bandgap, the centrosymmetric nature of its lattice and its wide transparency window across optical telecommunication wavebands hamper the realization of essential functionalities, including efficient light generation/amplification, fast electro-optical modulation, and reliable photodetection. Germanium, a well-established complement material in silicon chip industry, has a quasi-direct energy band structure in this wavelength domain. Germanium and its alloys are thus the most suitable candidates for active functions, i.e. bringing them to close to the silicon family of nanophotonic devices. Along with recent advances in silicon–germanium-based lasers and modulators, short-wave-infrared receivers are also key photonic chip elements to tackle cost, speed and energy consumption challenges of exponentially growing data traffics within next-generation systems and networks. Herein, we provide a detailed overview on the latest development in nanophotonic receivers based on silicon and germanium, including material processing, integration and diversity of device designs and arrangements. Our Review also emphasizes surging applications in optoelectronics and communications and concludes with challenges and perspectives potentially encountered in the foreseeable future. [ABSTRACT FROM AUTHOR]