Si1 xGex Research Articles

Effect of Ge4+-substituted on the structure characteristics and microwave/terahertz dielectric properties of ultra-low εr, high Q·f cordierite ceramics

In this study, Ge4+-substituted cordierite, Mg2Al4(Si1–xGex)5O18 ceramics, were successfully prepared by the traditional solid-state method to broaden its application potential. Notably, the excellent dielectric properties with εr = 4.90, Q·f = 128,200 GHz, and τf = −21.01 ppm °C–1 were achieved. The increase in εr value is mainly due to the heightened content of Ge4+ with high polarizability. The Q·f value improved by 2.21 times compared to the cordierite matrix, which can be primarily attributed to enhanced lattice energy, bond covalency, and hexagonal ring symmetry. The alteration in τf value arises from the variation of bond energy, bond strength, and distortion in the [MgO6] octahedra. These conclusions provide valuable insights for the design of silicate ceramics with higher Q·f values. In addition, the dielectric properties in the microwave and terahertz bands were compared. The higher Q·f and lower εr values in the terahertz band mainly result from the withdrawal of partial polarization mechanisms and differences in measurement methods. Mg2Al4(Si0.92Ge0.08)5O18 ceramics, demonstrating an ultra-low εr value of 4.54 and an ultra-high Q·f value of 286,533 GHz in the terahertz band, emerge as formidable contenders for future terahertz communications materials. Finally, a microstrip patch antenna was fabricated, achieving a bandwidth of 150 MHz at 4.78 GHz, which confirms the application in the n79 band for wireless communication.

Doping of thermoelectric nanostructured solid solution Si1–xGex (x ~ 0,3) with donor and acceptor impurities during the synthesis process by spark plasma sintering

Doping of thermoelectric nanostructured solid solution Si1–xGex (x ~ 0,3) with donor and acceptor impurities during the synthesis process by spark plasma sintering

Near infrared photoluminescence of Si1–xGex quantum dots fabricated by double hot Ge+/Si+ implantation into SiO2 layer

In this study, we developed very simple and ULSI (ultra large scale integration) compatible fabrication processes for group-IV (Si1–xGex and Si) semiconductor quantum dots (QDs) to apply hybrid ULSIs with photonic and electron devices, using double Ge+/Si+ hot-ion implantation into a SiO2 layer with larger bandgap EG and the post-furnace annealing. We successfully demonstrated the near-infrared (IR) photoluminescence (PL) from Si1–xGex-QDs. Transmission electron microscopy observations of single-crystallized Si1–xGex-QDs revealed that the diameter and the QD density were 3.6 ± 0.9 nm and (2.6 ± 0.4) × 1012 cm−2, respectively. In addition, Ge atoms were detected in the Si1–xGex-QDs by the energy dispersive x-ray spectroscopy analysis, and the Ge fraction of Si1–xGex-QDs was varied from 0.06 to 0.26 by changing the Ge ion dose. The increase in the PL intensity by forming gas annealing was attributed to the dangling-bond reduction by the H-atom termination method. The PL spectrum of Si1–xGex-QDs was fitted by PL components of two QD structures containing Si1–xGex and Si materials. The PL intensity and PL-peak photon energy of Si1–xGex-QDs strongly depended on the Ge fraction. The Si1–xGex-QDs achieved the maximum PL intensity at x ≈ 0.13. High PL-peak photon energy (∼1.31 eV) of Si1–xGex-QDs is attributed to the quantum confinement effect of carriers in QDs. Consequently, group-IV semiconductor QDs including Si1–xGex, Si, SiC, and C, through the simple hot-ion implantation into the SiO2 layer, exhibited a wide range of PL emissions from the near-IR to ultraviolet regions.

Composition Dependent Electrical Transport in Si1-x Gex Nanosheets with Monolithic Single-Elementary Al Contacts.

Si1-x Gex is a key material in modern complementary metal-oxide-semiconductor and bipolar devices. However, despite considerable efforts in metal-silicide and -germanide compound material systems, reliability concerns have so far hindered the implementation of metal-Si1-x Gex junctions that are vital for diverse emerging "More than Moore" and quantum computing paradigms. In this respect, the systematic structural and electronic properties of Al-Si1-x Gex heterostructures, obtained from a thermally induced exchange between ultra-thin Si1-x Gex nanosheets and Al layers are reported. Remarkably, no intermetallic phases are found after the exchange process. Instead, abrupt, flat, and void-free junctions of high structural quality can be obtained. Interestingly, ultra-thin interfacial Si layers are formed between the metal and Si1-x Gex segments, explaining the morphologic stability. Integrated into omega-gated Schottky barrier transistors with the channel length being defined by the selective transformation of Si1-x Gex into single-elementary Al leads, a detailed analysis of the transport is conducted. In this respect, a report on a highly versatile platform with Si1-x Gex composition-dependent properties ranging from highly transparent contacts to distinct Schottky barriers is provided. Most notably, the presented abrupt, robust, and reliable metal-Si1-x Gex junctions can open up new device implementations for different types of emerging nanoelectronic, optoelectronic, and quantumdevices.

Si1–xGex anode synthesis on plastic films for flexible rechargeable batteries

SiGe is a promising anode material for replacing graphite in next generation thin-film batteries owing to its high theoretical charge/discharge capacity. Metal-induced layer exchange (LE) is a unique technique used for the low-temperature synthesis of SiGe layers on arbitrary substrates. Here, we demonstrate the synthesis of Si1−xGex (x = 0–1) layers on plastic films using Al-induced LE. The resulting SiGe layers exhibited high electrical conductivity (up to 1200 S cm−1), reflecting the self-organized doping effect of LE. Moreover, the Si1−xGex layer synthesized by the same process was adopted as the anode for the lithium-ion battery. All Si1−xGex anodes showed clear charge/discharge operation and high coulombic efficiency (≥ 97%) after 100 cycles. While the discharge capacities almost reflected the theoretical values at each x at 0.1 C, the capacity degradation with increasing current rate strongly depended on x. Si-rich samples exhibited high initial capacity and low capacity retention, while Ge-rich samples showed contrasting characteristics. In particular, the Si1−xGex layers with x ≥ 0.8 showed excellent current rate performance owing to their high electrical conductivity and low volume expansion, maintaining a high capacity (> 500 mAh g–1) even at a high current rate (10 C). Thus, we revealed the relationship between SiGe composition and anode characteristics for the SiGe layers formed by LE at low temperatures. These results will pave the way for the next generation of flexible batteries based on SiGe anodes.

A physics-based drain current model for Si1-xGex source/drain NT JLFET for enhanced hot carrier reliability with temperature measurement

In this paper, we report, the hot carrier reliability issue in the Si1-xGex source/drain nanotube (NT) junctionless field-effect transistor (JLFET) with temperature variations. The surface potential, electric field and drain current have been formulated by developing a physics-based analytical model. SiGe in the source/drain regions creates valence band discontinuity of ΔEg = 0.23 eV which significantly increases the tunneling width at the channel/drain interface and therefore, results in a diminished L-BTBT action. The results demonstrate that at T = 500 K, drain current with the influence of interface trap charges in the Si1-xGex S/D architecture shows better immunity than the conventional NTJLFET. The Si1-xGex S/D enhances the reliability of analog/RF parameters such as transconductance (gm), intrinsic gain (gm/gd), cut-off frequency (fT), and gain-transconductance-frequency-product (GTFP), against the hot carriers. We have also explored the reliability with germanium (Ge) content, x and observed that for Ge content above x = 0.3, the reliability degrades in terms of higher electron temperature, reduced gm, and lower fT. The analytical results are verified and are in good agreement with results of Sentaurus TCAD simulations. The Si1–xGex S/D architecture combined with NT core gate can help relieve the HCI trap charge reliability for JLFETs leading to significantly improved analog/RF parameters.

Electrical properties of cation-substituted Ag7(Si1–xGex)S5I single crystals

High-quality single crystals of Ag7(Si1–xGex)S5I (x = 0.2, 0.4, 0.6, 0.8) solid solutions are grown from the solution–melt by vertical zone crystallization method. The measurements of electrical conductivity of Ag7(Si1–xGex)S5I solid solutions were performed using the impedance spectroscopy method within the frequency range from 10 Hz up to 2·106 Hz and temperature interval 293–383 K. Ionic and electronic components of electrical conductivity, as well as their ratios, were determined using the Nyquist plots.

Langmuir-Type Expressions for In-Situ Co-Doping of C with B or P in Si1–xGex Epitaxial Growth by Chemical Vapor Deposition

In-situ co-doping process of C with B or P in Si1−xGex (100) epitaxial growth by chemical vapor deposition (CVD) is investigated using SiH4–GeH4–SiH3CH3–B2H6 or PH3–H2 mixture. The in-situ doping of only C is explained quantitatively by the Langmuir-type adsorption and reaction at Si-Si, Si-Ge or Ge-Ge pair sites on the (100) surface. For in-situ co-doping of C with B, it is concluded that SiH4, GeH4, SiH3CH3 and B2H6 molecules are adsorbed and react at the pair sites and react at the B-occupied sites where B2H6 molecules have been adsorbed at the pair sites and additionally B2H6 molecules react at the C-occupied sites where SiH3CH3 molecules have been adsorbed at the pair sites. For in-situ co-doping of C with P, it is concluded that SiH4, GeH4, SiH3CH3 and PH3 molecules are adsorbed and react at the pair sites and only GeH4 molecules decompose at the P-occupied sites where PH3 molecules have been adsorbed self-limitedly on the (100) surface without the reactions at the C-occupied sites. From these results, Langmuir-type quantitative expressions of the experimental results are confirmed for in-situ co-doping of C with B or P in Si1–xGex (100) epitaxial growth by CVD.

Toward accurate electronic, optical, and vibrational properties of hexagonal Si, Ge, and Si1−xGex alloys from first-principle simulations

A new hexagonal phase of Si1−xGex alloys have been successfully synthesized through efforts in recent reports. Utilizing the combined first-principle calculations and special quasi-random model, we precisely investigated the structural, electronic, optical, and vibrational properties of hexagonal Si and Ge and disordered hexagonal Si1−xGex random alloys. We found a large negative deviation between the calculated lattice constants within the revised Perdew–Burke–Ernzerhof for solids functional and the linear fitting results. The electronic structures obtained by using the Tran–Blaha modified Becke–Johnson exchange potential confirm that hexagonal Si1−xGex (x > 0.625) alloys present direct bandgaps. Through solving the Bethe–Salpeter equation, the linear optical spectra of hexagonal Si and Ge are demonstrated. We reveal that the peaks of complex dielectric functions are redshifted with the addition of Ge atoms. Also, the real and imaginary parts exhibit strong anisotropy, which makes hexagonal Si1−xGex alloys potentially useful as nonlinear crystals. The transition is allowed in the infrared region for the hexagonal Si1−xGex (x > 0.625) alloys, and the linear optical spectra can be continuously tuned over a wide range of frequency with Ge addition in the infrared region. Furthermore, density-functional perturbation theory calculations were carried out to predict the off-resonance Raman activity. The results suggest that the vibrational modes of the Si–Si bond exhibit a strong dependency on the compositions, which provides a useful way to identify the most probable atomic configurations of hexagonal Si1–xGex alloys in future experiments.

New Strategies for Engineering Tensile Strained Si Layers for Novel n-Type MOSFET

We report a novel approach for engineering tensely strained Si layers on a relaxed silicon germanium on insulator (SGOI) film using a combination of condensation, annealing, and epitaxy in conditions specifically chosen from elastic simulations. The study shows the remarkable role of the SiO2 buried oxide layer (BOX) on the elastic behavior of the system. We show that tensely strained Si can be engineered by using alternatively rigidity (at low temperature) and viscoelasticity (at high temperature) of the SiO2 substrate. In these conditions, we get a Si strained layer perfectly flat and free of defects on top of relaxed Si1-xGex. We found very specific annealing conditions to relax SGOI while keeping a homogeneous Ge concentration and an excellent thickness uniformity resulting from the viscoelasticity of SiO2 at this temperature, which would allow layer-by-layer matter redistribution. Remarkably, the Si layer epitaxially grown on relaxed SGOI remains fully strained with -0.85% tensile strain. The absence of strain sharing (between Si1-xGex and Si) is explained by the rigidity of the Si1-xGex/BOX interface at low temperature. Elastic simulations of the real system show that, because of the very specific elastic characteristics of SiO2, there are unique experimental conditions that both relax Si1-xGex and keep Si strained. Various epitaxial processes could be revisited in light of these new results. The generic and simple process implemented here meets all the requirements of the microelectronics industry and should be rapidly integrated in the fabrication lines of large multifinger 2.5 V n-type MOSFET on SOI used for RF-switch applications and for many other applications.

Phonon dispersion of bulk Ge-rich SiGe: inelastic X-ray scattering studies

Group IV semiconductors, such as SiGe with a higher Ge fraction, are attracting attention as next-generation materials for high-mobility channel or thermal conductivity devices. Thus, we investigated the phonon dispersions of a Si1–xGex (x = 0.72) alloy crystal by the inelastic X-ray scattering (IXS) method. In this method, measurement with an X-ray beam with a small spot size of 75 μm and resolution of millielectronvolts is possible due to the synchrotron technique. The longitudinal and transverse phonon spectra of optical and acoustic modes were measured from the Γ to the X point in the phonon energy band (0–70 meV) with millielectronvolt energy resolution. SiGe showed dispersion characteristics similar to those of Si and Ge crystals. It was confirmed that the IXS method is useful for obtaining properties of phonon dispersion.

Получение и морфологические исследования эпитакcиальных слоев твердого раствора Si1–xGex

The article shows the selection of the optimal process regime for the growth of epitaxial layers of Si1–xGex solid solutions from tin and gallium solution – melt on a Si<111> substrate, with the lowest dislocation densities that we experimentally achieved. An exponential relationship was found between the values of the dislocation density and the film thickness.With a smooth variable composition of the structure, respectively, by smoothly changing the lattiece parameters of the graded-gap solid solution, structurally perfect epitaxial layers Si1–xGex (0 < x < 1) were obtained

Pressure and Temperature Dependence of Energy Gap in SiC and Si1-xGex

The effect of pressure on energy gap for IV-IV compound SiC and Si1-xGex alloy have been investigated and evaluated by using Birch-Murnaghan equation of state (EOS) and Bardeen equation of state. Ambiguity in the effect of pressure and temperature on Eg of different SiC polytypes (3C, 4H, 6H) have been investigated and attributed. Variation of Eg in Si1-x Gex evaluated and an interpretation, for it, has been suggested.

Temperature-induced valence transition in EuNi2(Si1–xGex)2 investigated by high-energy resolution fluorescence detection X-ray absorption spectroscopy

Electronic structures of the temperature-induced valence transition system EuNi2(Si1–xGex)2 with x = 0.70, 0.79, 0.82 have been investigated by means of high-energy resolution fluorescence detection X-ray absorption spectroscopy (HERFD-XAS). The HERFD-XAS spectra clearly change their intensities of Eu2+ and Eu3+ components which directly reflect the temperature-induced valence transition. For x = 0.70, gradual spectral change exhibits a continuous valence transition, while drastic changes for x = 0.79 and 0.82 indicate first-order valence transitions. High-energy resolution measurements made it possible to observe additional fine structures which are recognized more clearly below the transition temperature. Existence of these fine structures suggests that many-body effect plays an important role in the temperature-induced valence transition of this system. The variation of Eu mean valence estimated from the HERFD-XAS spectra for each x correlates with that of magnetic susceptibility.

Study of SiGe Crystal Growth Interface Processed in Microgravity

A Si1–xGex (x ∼ 0.5) crystal measuring 10 mm in diameter was grown by the traveling liquidus zone method using the Gradient Heating Furnace aboard the International Space Station. We quantitatively...

Effect of Boron Doping on High-Resolution X-Ray Diffraction Metrology

The effect of boron (B) doping on high-resolution X-ray diffraction (HXRD) metrology has been investigated. Twelve samples of Si1–xGex films were epitaxially grown on Si (100) substrates with different thicknesses, germanium (Ge) concentrations and with/without B dopants. Secondary ion mass spectroscopy (SIMS) and HXRD were employed for measurements of B doping, Ge concentration, strain, and thickness of the layers. The SIMS results show the absence of B in two samples while the rest of the samples have B doping in the range of 8.40 × 1018–8.7 × 1020 atoms/cm3 with Ge concentration of 13.3–55.2 at.%. The HXRD measurements indicate the layers thickness of 7.07–108.13 nm along with Ge concentration of 12.82–49.09 at.%. The difference in the Ge concentration measured by SIMS and HXRD was found to deend on B doping. For the undoped samples, the difference is ~0.5 at.% and increases with B doping but with no linear proportionality. The difference in the Ge concentration was 7.11 at.% for the highly B-doped (8.7 × 1020 atoms/cm3) sample. The B doping influences the Si1–xGex structure, causing a change in the lattice parameter and producing tensile strains shifting Si1–xGex peaks towards Si (100) substrate peaks in the HXRD diffraction patterns. As a result, Vegard’s law is no longer effective and makes a high impact on the HXRD measurement. The comparison between symmetric (004) and asymmetric (+113, +224) reciprocal space mappings (RSM) showed a slight difference in Ge concentration between the undoped and lower B-doped samples. However, there is a change of 0.21 at.% observed for the highly doped Si1–xGex samples. RSM’s (+113) demonstrate the small SiGe peak broadening as B doping increases, which indicates a minor crystal distortion.

Effect of Doping in Controlling the Structure, Reactivity, and Electronic Properties of Pristine and Ca(II)-Intercalated Layered Silicene

Hybrid two-dimensional (2D) materials composed of carbon- and germanium-doped silicene monolayers, denoted as Si1–xCx, Si1–xGex, and Si1–2xCxGex (0 ≤ x ≤ 1), were investigated by first-principles calculations. Their structural features can be understood on the basis of Vegard’s law. The lattice parameters were found to correlate well with the arithmetic mean of the percentage doping of the individual constituents. The electronic band gap showed an interesting bell-shaped behavior for Si1–xCx with respect to doping, wherein Eg increased from 0 (for x = 0) to a maximum (for x = 0.5) and eventually decreased again to 0 (for x = 1). Clearly controlled carbon doping of the silicene monolayer was found to open up the band gaps and also provides a means of harvesting solar energy for semiconductor and photovoltaic applications. In addition to pristine monolayer silicene, we also investigated the effects of Ca(II)-intercalated multilayer silicene/germanene as available in the van der Waals mineral phases of CaSi2 and CaGe2. The stabilities and reaction energies for hydrogenation, fluorination, and mixed hydrogenation–fluorination for these Ca(II)-intercalated structures were compared with those of pristine and doped monolayer silicene. Optical absorption calculations demonstrated that doped monolayers and Ca(II)-intercalated multilayer silicene/germanene have strong photoabsorption in the visible light region. The presence of Ca(II) stabilizes the silicene/germanene layers, and the Ca(II) also affects the electronic structures of these 2D materials.

Site‐Specific Substitution Preferences in the Solid Solutions Li12Si7–xGex, Li12–yNaySi7, Na7LiSi8–zGez, and Li3NaSi6–vGev

The mixed silicide‐germanides Li12Si7–xGex, Na7LiSi8–zGez, and Li3NaSi6–vGev which could serve as potential precursors for Si1–xGex materials were synthesized and characterized by X‐ray diffraction methods. The full solid solution series Li12Si7–xGex (0 ≤ x ≤ 7) is easily accessible from the elements and features preferential occupation of the more negatively charged crystallographic tetrel positions by Ge, which is the more electronegative element. In case of Na7LiSi8–zGez a broad solid solution range of 1.3 ≤ x ≤ 8 is available but the ternary silicide Na7LiSi8 could not be obtained by the tested methods of synthesis. The solubility of Ge in Li3NaSi6–vGev is highly limited to a maximum of v ≈ 0.5, and again the formally more negatively charged tetrel positions are preferred by Ge. Additionally, the two crystallographic Li positions in Li12Si7 with unusually large displacement parameters can be partially substituted by Na in Li12–yNaySi7 with 0 ≤ y ≤ 0.6. The statistical mixing of Li and Na in this solid solution contrasts the typical ordering of Li and Na in most ternary tetrelides.

Conditions of growth of high-quality relaxed Si1–x Ge x layers with a high Ge content by the vapor-phase decomposition of monogermane on a sublimating Si hot wire

The conditions of the epitaxial growth of high-quality relaxed Si1–x Ge x layers by the combined method of the sublimation molecular-beam epitaxy and vapor-phase decomposition of monogermane on a hot wire are considered. The combined growth procedure proposed provides a means for growing Si1–x Ge x layers with a thickness of up to 2 µm and larger. At reduced growth temperatures (T S = 325–350°C), the procedure allows the growth of Si1–x Ge x layers with a small surface roughness (rms ≈ 2 nm) and a low density of threading dislocations. The photoluminescence intensity of Si1–x Ge x :Er layers is significantly (more than five times) higher than the photoluminescence intensity of layers produced under standard growth conditions (T S ≈ 500°C) and possess an external quantum efficiency estimated at a level of ~0.4%.

The thermovoltaic effect in variband solid solution Si1–x Ge x (0 ≤ x ≤ 1)

The thermovoltaic effect in films of variband solid solution Si1–xGex (0 ≤ x ≤ 1) has been observed for the first time. The samples comprised n-Si–p-Si1–xGex (0 ≤ x ≤ 1) heterostructures grown by liquid phase epitaxy. An electromotive force within 0.05–0.3 mV and a current of 0.0025–0.0035 μA appeared on heating samples in a temperature range from 40 to 250°C.