Si Samples Research Articles

Structural and Functional Properties of Si and Related Semiconducting Materials Processed by High-Pressure Torsion

We report on the HPT processing of Si and related semiconducting materials, and discuss the phase transformation and the electrical, thermal, and optical properties. In-situ synchrotron x-ray diffraction revealed that the metastable bc8-structure Si-III and r8-structure Si-XII in the HPT-processed Si samples gradually disappeared and hexagonal-diamond Si-IV appeared during annealing up to 473 K. The formation of Si-III/XII in the samples processed at a nominal pressure of 6 GPa indicated the strain-induced phase transformation from Si-I to a high-pressure tetragonal Si-II phase during HPT processing, and a following phase transformation from Si-II to Si-III/XII upon decompression. The resistivity decreased with increasing the number of anvil rotations due to the formation of semimetallic Si-III. The thermal conductivity of Si was reduced to ~3 W m–1 K–1 after HPT processing. A weak and broad photoluminescence peak associated with Si-I nanograins appeared in the visible light region after annealing. Metastable bc8-Si0.5Ge0.5 with a semimetallic property was formed by HPT processing of a traveling-liquidus-zone-grown Si0.5Ge0.5 crystal. These results indicate that the application of HPT processing to Si and related semiconductors pave the way to novel devices utilizing nanograins and metastable phases.

In-plane thermal diffusivity determination using beam-offset frequency-domain thermoreflectance with a one-dimensional optical heat source

We present an innovative contactless method suitable to study in-plane thermal transport based on beam-offset frequency-domain thermoreflectance using a one-dimensional heat source with uniform power distribution. Using a one-dimensional heat source provides a number of advantages as compared to point-like heat sources, as typically used in time- and frequency-domain thermoreflectance experiments, just to name a few: (i) it leads to a slower spatial decay of the temperature field in the direction perpendicular to the line-shaped heat source, allowing to probe the temperature field at larger distances from the heater, hence, enhancing the sensitivity to in-plane thermal transport; (ii) the frequency range of interest is typically <100 kHz. This rather low frequency range is convenient regarding the cost of the required excitation laser system but, most importantly, it allows the study of materials without the presence of a metallic transducer with almost no influence of the finite optical penetration depth of the pump and probe beams on the thermal phase lag, which arises from the large thermal penetration depth imposed by the used frequency range. We also show that for the case of a harmonic thermal excitation source, the phase lag between the thermal excitation and thermal response of the sample exhibits a linear dependence with their spatial offset, where the slope is proportional to the inverse of the thermal diffusivity of the material. We demonstrate the applicability of this method to the cases of: (i) suspended thin films of Si and PDPP4T, (ii) Bi bulk samples, and (iii) Si, glass, and highly-oriented pyrollitic graphite (HOPG) bulk samples with a thin metallic transducer. Finally, we also show that it is possible to study in-plane heat transport on substrates with rather low thermal diffusivity, e.g., glass, even using a metallic transducer. We achieve this by an original approach based on patterning the transducer using focused ion beam, with the key purpose of limiting in-plane heat transport through the thin metallic transducer.

First-principles-aided evaluation of the Nernst coefficient beyond the constant relaxation time approximation

The solution of the Boltzmann Transport Equation (BTE) under open voltage conditions and in the presence of simultaneously applied magnetic field and temperature gradient results in the so-called Nernst response of the electrons. The calculation of the Nernst coefficient using first-principles calculations as an extension of the BoltzWann code and under Jones–Zener expansion valid for weak magnetic fields has been the subject of our previous work which provided a general framework for the calculation of the Nernst effect but was not able to capture the experimental results due to the constant relaxation time approximation used. In Contrast to the Seebeck coefficient which is not sensitive to the details of the relaxation times, the Nernst coefficient is proportional to the carrier mobility and hence is greatly affected by the relaxation times. In this work, we focus on the inclusion of the energy-dependent electron–phonon and the electron–impurity relaxation times in our formalism. Using the developed formalism, we successfully reproduced the experimental data of several samples. In this paper, we report our results on Ge, Si, and InSb samples. However, the code is not limited to the reported samples and supports a wide range of materials.

Investigation of magnetic behavior of non-stoichiometric Co1.75Mn0.5Fe0.75Si and Co1.5MnFe0.5Si compositions associated with their Co2FeSi and Co2MnSi parent alloys

Full Heusler Co2MnSi and Co2FeSi alloys have demonstrated half-metallic behavior with their ferromagnetic ground state having magnetic moments of ∼ 5.0 μB/f.u. and ∼ 6.0 μB/f.u. respectively with Curie temperature around 1100 K. In this article, we have investigated the magnetic properties of non-stoichiometric Co1.75Mn0.5Fe0.75Si and Co1.5MnFe0.5Si quaternary Heusler alloys. X-Ray diffraction measurement for both samples has revealed the signature of quaternary LiMgPdSn prototype parent phase structure (Space group-F-43 m, 216) manifested with the super-reflection peaks (111 and 200) and high intense peak (220). Interestingly, inter-martensitic phase has been observed in the Co1.5MnFe0.5Si sample even at room temperature as indicated by the 7M modulated peaks in the XRD pattern. Transmission electron microscopy (TEM) along with selected area electron diffraction pattern of both the alloys has also exhibited the FH parent phase. Magnetic measurements have been performed to reveal the magnetization variation with the applied magnetic field (M−H) which exhibited the saturation of magnetization of both the samples around ± 1.5 Tesla magnetic field. Zero field cooled (ZFC) and field cooled (FC) data have been taken via cooling down these samples from 300 K to 5 K temperature in the zero and 0.5 Tesla field respectively which revealed few meta-magnetic transitions such as martensitic and inter martensitic transition in the magnetization versus temperature curve.

Three-dimensional investigation of fragment distribution in Al – 7wt.% Si solidified in microgravity

Three-dimensional (3D) reconstruction of the microstructure of Al – 7 wt.% Si samples solidified in microgravity conditions on board of the International Space Station was obtained from serial-sectioning images. The main objective was to quantify the number of dendrite fragments issued from the solidification process in absence of buoyancy force and with motionless dendrite fragments on contrary to ground-based experiments. The results show that the number of fragments strongly depends on the dendrite network configuration. More fragments are observed in the sample containing several dendrites with different orientations compared to a sample with well-aligned dendrites. Moreover, it has been found that the highest number of fragments is mainly located in the region corresponding to an incipient grain boundary where dendrites with different orientations compete. Indeed, in this region solute accumulates and the microstructure is finer which is more prone to fragmentation of dendritic arms growing in this region. Thus, a mechanism that leads to the formation of dendrite fragmentation is identified: dendrite misorientation during solidification.

INFLUENCE OF IMPURITY NI AND CU ATOMS ON THE ELECTROPHYSICAL PROPERTIES OF SI

The paper presents the results of studies of the electrophysical properties of Si, doped Ni and Cu samples. It is revealed that a decrease in the mobility of charge carriers in the temperature range of 120÷320 K is of particular importance in increasing the resistivity of samples.

Investigation of the Temperature Dependence of Volt-Ampere Characteristics of a Thin-Film Si3N4 Memristor

The compatibility of memristor materials with advanced complementary metal-oxide-semiconductor (CMOS) technology is a key factor for microelectronics element base manufacturing. Therefore, we continued studying previously fabricated CMOS-compatible Ni/Si3N4/SiO2/p+-Si samples. We approximated volt-ampere characteristics (VAC) at different temperatures using the general form of the spatial charge-limiting current (SCLC) equation assuming exponential and Gaussian trap distribution within the band gap of Si3N4. Our approximation demonstrated better experimental data matching compared to previous work, where the approximation was based on the uniform trap distribution law. Further, we performed another additional sample measurement set of the samples to evaluate the parameters of the low-resistance state (LRS) variations at different temperatures. Analysis of these measurements allowed us to estimate the temperatures at which the samples will retain LRS for 10 years.

Morphological and Optical Study of Black P- Silicon Textured in KOH Bath

This paper reports the temperature and the concentration dependence of anisotropic etching for (100) p-Silicon in an aqueous KOH solution etching rate of wet etching has been experimentally determined with varying concentrations and the temperature of the KOH solution. The texturing process was managed at different etching durations ( 20 min, 40 min, and 60 min). XRD test showed that the lowest value of grain size was 5.0 nm (obtained with the highest porosity percentage of 50% with 4.5% KOH concentration for 60 min). FESEM test showed that the pore diameter increased with increasing etching time. The lowest reflectance value was (2.8 % at 550 nm wavelengths for samples treated with 4.5% KOH concentration for 60 min etching time. The refractive index value was 1.8 for the same black Si sample, also Hall test is introduced.

Laser‐Assisted Growth of Fe3O4 Nanoparticle Films on Silicon Substrate in Open Air

This work presents a growth of Fe3O4 nanoparticle films on silicon substrate. The iron oxide is deposited applying a pulsed laser deposition technique. The process is performed in open air in the absence and presence of external magnetic field. In fact, the morphologies of the obtained Fe3O4–Si samples are similar. The Fe3O4 nanoparticles are spherical with average diameters of 30 nm and are densely agglomerated on the Si substrate. The Fe3O4–Si material prepared in the absence of magnetic field has revealed more intense signals during X‐ray diffraction and Raman measurements. The magnetic investigations indicate that the Fe3O4 nanoparticles are significantly coupled with the Si substrate and do not exhibit superparamagnetic behavior. Moreover, the Verwey transition is 98 K for both investigated Fe3O4–Si samples.

Photoinduced Microwave Permittivity of Semiconductors: Exciton Mechanism

Significant differences observed in the behavior of photoinduced permittivity ε of semiconductors in the gigahertz (GHz) and terahertz (THz) ranges are explained within the framework of the exciton mechanism by the different position of these ranges relative to the frequencies of exciton interlevel transitions. The measurements in the GHz range of the photoinduced changes of quantities Imε(P_λ) and Reε(P_λ) of CdS, CdSe and Si samples in a waveguide resonator (f = 4.7 GHz) and transmittance T of Si samples in free space (f = 8–36 GHz ) under fiber-optic irradiation (P_λ = 0–370 mW and λ = 0.97 μm) that exhibit non-Drude response prove the theoretical conclusions: an increase in Reε^(GHz)(P_λ) with increasing P_λ and an increase in transmittance T with decreasing frequency f at fixed power P_λ.

Superconductivity in the cobalt-doped V3Si A15 intermetallic compound

The A15 structure of superconductors is a prototypical type-II superconductor that has generated considerable interest since the early history of superconducting materials. This paper discusses the superconducting properties of previously unreported V3−x Co x Si (0 ⩽ x ⩽ 0.30) alloys. It is found that the lattice parameter decreases with increasing cobalt-doped content and leads to an decreased residual resistivity ratio value of the V3−x Co x Si system. Meanwhile, the superconducting transition temperature (Tc ) also decreases with increasing cobalt-doped content. Furthermore, the fitted data show that the increase of cobalt-doped content also reduces the lower/upper critical fields of the V3−x Co x Si system. Type-II superconductivity is demonstrated in all V3−x Co x Si samples. With higher Co-doped content, V3−x Co x Si (0.15 ⩽ x ⩽ 0.30) alloys may have superconducting and structural phase transitions in low-temperature regions. As the electron/atom ratio increases, the Tc variation trend of V3Si is as pronounced as in crystalline alloys and monotonically follows the trend observed for amorphous superconductors.

External Gettering of Metallic Impurities by Black Silicon Layer

Black silicon (b‐Si) has many attractive properties and is currently being adopted in various fields of semiconductor technology. It is shown here that b‐Si during thermal activation may serve as an external gettering layer to remove metallic impurities and associated defects from bulk Si. The gettering efficiency by b‐Si is estimated according to the results of studying the resistivity, defect density, interstitial iron concentration, and effective minority carrier lifetime on gettered test and ungettered reference Si samples. It is shown that in the thermal oxidation process, the b‐Si layer serves as an effective drain for excess iron atoms and other fast‐diffusing impurities, thereby significantly reducing the density of oxidation‐induced stacking faults in Si. In addition, the resistivity of the substrates decreases, and the bulk carrier lifetime increases significantly. Finally, gettering by b‐Si is introduced into the solar cells fabrication process and its effect on solar cell current–voltage characteristics is investigated. It has been shown that all electronic parameters of the solar cells are improved. The conversion efficiency of ungettered solar cells is 16.8%, and for gettered solar cells, depending on the oxidation temperature, it increases by 1.36–1.96%.

Cyclic Voltammetry and Impedance Measurements of Graphene Oxide Thin Films Dip-Coated on n-Type and p-Type Silicon

Despite the increasing interest in graphene, a less studied aspect is the enhancement of silicon (Si) performances due to the interaction with graphene-based materials. In this study, cyclic voltammetry and electric impedance measurements are performed on graphene oxide (GO) dip-coated on n-type and p-type Si samples. The electrical properties of GO on n-type Si samples are dramatically enhanced: The conductivity and the photocurrent meaningfully increase in comparison to bare n-type Si. Such findings could be used in a wide variety of optoelectronic applications, improving GO future applicability in the Si semiconductor industry.

Определение растворимости кобальта в монокристаллическом кремнии методом нейтронно-активационного анализа

Abstract. The possibility of instrumental neutron activation analysis is revealed for determining the solubility of cobalt in single-crystal silicon. It was shown that in n-Si in the diffusion temperature range of 1000  1250 0С the total solubility of the 60Co impurity varies within the concentration range of 2.8 ∙ 1014  9 ∙ 1015 cm-3, and the electrically active concentration grows from 1013 to 3 ∙ 1014 cm-3. In order to reduce the error in determining the concentration of 60Co in doped Si samples, it is suggested to use the parent stable isotope rather than the daughter cobalt radionuclide.

Role of interfacial nickel silicides in shaping magnetic anisotropy in nickel films grown on Silicon substrates

Using different experimental techniques such as X-ray reflectivity, X-ray diffraction, X-ray photoelectron spectroscopy and magneto-optical Kerr effect (MOKE) microscopy, the structural and magnetic properties of Ni films grown on Si substrates are investigated. Various Ni-silicide phases are found to be formed at the Ni–Si interface as a function of depth following the sequence Ni-Ni2Si-NiSi-NiSi2 from the nickel to silicon side. This has been explained in terms of the effective heat of formation and inter-diffusion of the elements at the interface. In-plane magnetic anisotropy of the system is investigated by measuring in-plane magnetization using MOKE microscopy. The film exhibits an uniaxial in-plane magnetic anisotropy. An anomalous behavior, i.e., the collapse of the hard axis, has also been observed. This anomaly has been explained in terms of the creation of V-state domains during the magnetization reversal process at the hard axis. Interestingly, in-plane magnetic anisotropy could not be found in a Ni film grown with a Pt buffer layer on the Si substrate. Ni-silicide phases could not be detected in this system. This may suggests that the formation of silicides and diffusion at the interface causes the atypical magnetic anisotropy in Ni–Si sample.

Electronic transport properties of Ti-supersaturated Si processed by rapid thermal annealing or pulsed-laser melting

In the scope of supersaturated semiconductors for infrared detectors, we implanted Si samples with Ti at high doses and processed them by rapid thermal annealing (RTA) to recover the crystal quality. Also, for comparative purposes, some samples were processed by pulsed-laser melting. We measured the electronic transport properties at variable temperatures and analyzed the results. The results indicate that, for RTA samples, surface layers with a high Ti concentration have negligible conductivity due to defects. In contrast, the implantation tail region has measurable conductivity due to very high electron mobility. This region shows the activation of a very shallow donor and a deep donor level. While deep levels have been previously reported for Ti in Si, such a shallow level has never been measured, and we suggest that it originates from Ti-Si complexes. Finally, a decoupling effect between the implanted layer and the substrate seems to be present, and a bilayer model is applied to fit the measured properties. The fitted parameters follow the Meyer–Neldel rule. The role of the implantation tails in Si supersaturated with Ti is revealed in this work.

Comparison of SiNx‐Based Surface Passivation Between Germanium and Silicon

Germanium (Ge) has attracted much attention as a promising channel material in nanoscale metal–oxide–semiconductor devices and near‐infrared sensing because of its high carrier mobilities and narrow bandgap, respectively. However, efficient passivation of Ge surfaces has remained challenging. Herein, silicon nitride (SiNx)‐based passivation schemes on Ge surfaces are studied and the observations are compared to Si counterparts. These results show that instead of a high positive charge density (Qtot) that is found in SiNx‐passivated Si samples, similar Ge samples contain a high amount of negative Qtot (in the range of 1012 cm−2). The maximum surface recombination velocity of the samples is shown to reduce by a factor of three in both Si and Ge samples by a post‐deposition anneal at 400 °C. The SiNx‐coated samples are capped with an atomic‐layer‐deposited aluminum oxide (Al2O3) layer, which reduces the midgap interface defect density (Dit) after annealing to 7 × 1010 and 4 × 1011 cm−2 eV−1 in Si and Ge, respectively. Interestingly, while the Al2O3 capping seems to have no impact on Qtot of the Si samples, it turns the stack virtually neutral (∼−1.6 × 1011 cm−2) on Ge. The presented SiNx‐based passivation schemes are promising for optoelectronic devices, where a low Dit and/or a low charge are favored.

Structural, optical, and electrical properties of V2O5 thin films: Nitrogen implantation and the role of different substrates

This report investigates the effect of substrate and nitrogen (16 keV N+) ion implantation on the structural, morphological, compositional, and electrical properties of V2O5 thin films which are grown by thermal evaporation on various substrates, including glass, Si, and sapphire (termed V2O5:Gl, V2O5:Si, and V2O5:Sp, respectively). Structural analysis showed the formation of the mixed (α, and β-V2O5) phases on all substrates; however, the β-V2O5 phase is highly dominant in the V2O5:G and V2O5:Si samples. A deformation in the β-phase of V2O5 thin film under ion implantation-induced strain results in a change of crystallite size. Irradiation suppresses XRD peaks in relative intensities, indicating partial amorphization of the film with defect formation. Microstructural analysis confirmed the formation of uniform-sized nanorods for V2O5:Si, whereas isolated crystallites were formed for other types of substrates. Thermal conductivity may influence the size and shapes of V2O5 crystallite forms on different surfaces. Silicon absorbs heat more effectively than sapphire or glass, resulting in nanorod formation. A decrease in optical bandgap and electrical conduction has been observed due to increased oxygen vacancies, induced electron scattering, and trapping centres on N+ implantation. The present study thus offers the unique advantage of simultaneous reduction in optical band-gap and conductance of V2O5 thin films, which is important for optoelectronic applications.

Toward Probing Surface Magnetism with Highly Charged Ions

X-rays produced during collisions between Highly Charged Ions (HCI) and sample surfaces can potentially be used to investigate the surface’s magnetic properties, taking advantage of the (partial) conservation of the spin of the electrons captured by the ion during the collision. We conducted studies to characterize the X-ray detection system and to determine, with a sub-degree accuracy, the incident angle between the incoming ions and the sample surfaces. A series of proof-of-principle experiments are presented involving an Ar17+ ion beam interacting with a nonmagnetic Si sample. The obtained X-ray spectra show a significant dependency in terms of X-ray yield and energy on the ion incidence angle. These findings will be used to guide future ion–magnetic surface studies.

Influence of silicon particle morphology on laser-induced plasma properties

In this work, Si particles of varying sizes and a bulk Si wafer are exposed to high-energy nanosecond-pulsed laser excitation. The subsequent laser-induced plasma is characterized using a suite of diagnostic techniques, including spatiotemporal species imaging via high-speed videography and high-resolution gated spectroscopy. The intensity and location of various species in the plasma (e.g., Si I and Si II) are tracked as a function of time over two time regimes, 2–10 μs and 20–80 μs, and show differences in impurities and peak intensities between the various particle sizes and compared to the Si wafer. Electron densities under these conditions decrease from ≈1.8 to 0.8 × 1017 cm−3 from 2 to 8 μs, while plasma excitation temperatures determined from the Boltzmann method range from 9200 to 8000 K over the same time window. The powdered Si samples have characteristically larger and more intense plasmas than the wafer sample. The laser-induced air-shock from energetic materials (LASEM) method was employed on these materials, in concert with their acoustic response, to establish their relative microsecond energy releases. While the powders have similar laser-induced shock velocities, they appear to have differences in their acoustic response which roughly scales as a function of plasma carbon content. The proposed reasons for these shock and acoustic trends are discussed, which include particle size and morphology, surface impurities, and dispersion and flow within the plasma.