Defects In Si Research Articles

Reactions of Hydrogen-Passivated Silicon Vacancies in α-Quartz with Electron Holes and Hydrogen.

We used density functional theory with a hybrid functional to investigate the structure and properties of [4H]Si (hydrogarnet) defects in α-quartz as well as the reactions of these defects with electron holes and extra hydrogen atoms and ions. The results demonstrate the depassivation mechanisms of hydrogen-passivated silicon vacancies in α-quartz, providing a detailed understanding of their stability, electronic properties, and behaviour in different charge states. While fully hydrogen passivated silicon vacancies are electrically inert, the partial removal of hydrogen atoms activates these defects as hole traps, altering the defect states and influencing the electronic properties of the material. Our calculations of the hydrogen migration mechanisms predict the low energy barriers for H+, H0, and H-, with the lowest barrier of 0.28 eV for neutral hydrogen migration between parallel c-channels and a similar barrier for H+ migration along the c-channels. The reactions of electron holes and hydrogen species with [4H]Si defects lead to the breaking of O-H bonds and the formation of non-bridging oxygen hole centres (NBOHCs) within the Si vacancies. The calculated optical absorption energies of these centres are close to those attributed to individual NBOHCs in glass samples. These findings can be useful for understanding the role of [4H]Si defects in bulk and nanocrystalline quartz as well as in SiO2-based electronic devices.

Coherence of NV defects in isotopically enriched 6H-28SiC at ambient conditions

The unique spin-optical properties of NV defects in SiC, coupled with silicon carbide's advanced technology compared to diamond, make them a promising candidate for quantum technology applications. In this study, using photoinduced pulse ESR at 94 GHz (3.4 T), we reveal the room temperature spin coherence of NV defects in 6H-28SiC, purified to reduce 29Si concentration to ≈1%, four times below its natural level. We demonstrate room temperature (300 K) Hahn-echo coherence time T2 = 23.6 μs, spin–lattice relaxation time T1 = 0.1 ms, and coherent control over optically polarized NV spin states through Rabi nutation experiments. We reveal long inhomogeneous dephasing time T2* = 1.5 μs, which is about five times greater than that measured for NV defects in SiC with natural isotopic content. Our observations highlight again the potential of NV defects in 6H-28SiC, which exhibit near-infrared optical excitation and emission properties compatible with O-band fiber optics, as promising candidates for applications in quantum sensing, communication, and computation.

Negligible Influence of C-related Defect on the Barrier Properties of Ti3C2T2/SiC Contacts: A First-Principles Study

The nature of the metal/semiconductor (M/S) contact (Ohmic or Schottky) in electronic devices can greatly affect the electronic properties of the component. The effective regulation of Schottky barrier height (SBH) has great importance for the successful operation of any electronic device. This paper demonstrates that the Ti3C2T2/SiC interface can effectively suppress the Fermi level pinning (FLP) effect through van der Waals stacking. By investigating the effects of the most probable C-related defect, namely carbon substitutional doping at silicon sites (CSi defects), on the contact performance of Ti3C2T2/SiC. It is found that CSi defects do not affect the contact type of Ti3C2T2/SiC and have little impact on the tunneling barrier. In addition, the SBH of Ti3C2T2/SiC could be modulated by a vertical electric field, without altering the tunneling barrier. The modulation is also not influenced by the CSi defects. Furthermore, based on the calculated Schottky and tunneling barriers, Ti3C2(OH)2 is the most compatible electrode with 2D SiC among the Ti3C2T2, even in the presence of CSi defects in SiC.

Enhanced thermoelectric performance of silicon powder arrays by remotely doping

We report improved thermoelectric (TE) properties of mesostructured silicon powder arrays simply prepared by die-pressing without sintering. In contrast to bromoethane's modest effect, the symmetric dibromoethane molecule coupling could significantly increase the conductivity of Si powder array TE device, from 12.7 S cm−1 of a silicon powder array to 62.3 S cm−1, which is possibly caused by the high electronic transmission probability of symmetric organic molecule–Si crystal coupling, and additionally enhanced by Si bandgap narrowing and defect states of an organic–inorganic interface identified by UV–vis absorption spectra and photoluminescence spectroscopy. Boosted by the very low thermal conductivity (0.58 W m−1 K−1), the dimensionless figure of merit, the ZT value of an Si powder array remotely doped by dibromoethane, ∼0.173, was obtained at 385 K, which is about 17 times higher than that of the bulk Si. An Si–organic hybrid TE device shows potentials to approach the threshold of practical applications with moderate ZT performance and low cost.

Artificial-neural-network descriptor enhancing accuracy of machine-learning interatomic potential and its application to lattice defects in Si

Artificial-neural-network descriptor enhancing accuracy of machine-learning interatomic potential and its application to lattice defects in Si

Elimination of Si-C Defect on Wafer Surface in High-Temperature SPM Process Through Nitrogen Purge in 300-mm Single-Wafer Chamber

Elimination of Si-C Defect on Wafer Surface in High-Temperature SPM Process Through Nitrogen Purge in 300-mm Single-Wafer Chamber

Temperature Effects of Nuclear and Electronic Stopping Power on Si and C Radiation Damage in 3C-SiC.

Silicon carbide has been considered a material for use in the construction of advanced high-temperature nuclear reactors. However, one of the most important design issues for future reactors is the development of structural defects in SiC under a strong irradiation field at high temperatures. To understand how high temperatures affect radiation damage, SiC single crystals were irradiated at room temperature and after being heated to 800 °C with carbon and silicon ions of energies ranging between 0.5 and 21 MeV. The number of displaced atoms and the disorder parameters have been estimated by using the channeling Rutherford backscattering spectrometry. The experimentally determined depth profiles of induced defects at room temperature agree very well with theoretical calculations assuming its proportionality to the electronic and nuclear-stopping power values. On the other hand, a significant reduction in the number of crystal defects was observed for irradiations performed at high temperatures or for samples annealed after irradiation. Additionally, indications of saturation of the crystal defect concentration were observed for higher fluences and the irradiation of previously defected samples.

Enhancing Charging Efficiency with Lithium Silicate in Silicon Composite Anode Materials Through Lithiothermic Reduction Reaction Synthesis

AbstractThis study synthesizes silicon (Si) powders with lithium silicates including lithium orthosilicate (Li4SiO4), lithium metasilicate (Li2SiO3), and lithium disilicate (Li2Si2O5), creating a composite structure of crystalline Si within a LixSiyOz matrix through the lithiothermic reduction reaction (LTRR) process. The reduction of Li‐ion consumption of the anode is investigated by 1) initial solid electrolyte interphase (SEI) layer formation, 2) SEI layer formation in response to Si expansion‐induced damage, 3) trapping of Li ions at Si defects, and 4) side reactions during initial charge and discharge cycles. Si/LixSiyOz electrode exhibits a specific capacity of 1522.2 mAh g−1 and an initial coulombic efficiency of 83.5%. The effect of the calendering process is observed, and a pressurization condition of 5000 kgf cm−2 or less is set, and the ICE is improved to 93.4%–96%. Si/LixSiyOz electrodes outperform pure crystalline Si electrodes in specific capacity (7.3%), ICE (42%), and retention characteristics (17%). The integration of the LixSiyOz matrix into Si anodes enhances Li‐ion transport and partially suppresses Si expansion. Additionally, the Si/LixSiyOz electrode exhibits superior rate capability in the 0.2–1.6 A g−1 range.

Investigating the impact of physical vapour deposition of palladium on electron-irradiated silicon substrates

This study reports on the effect of resistive physical vapour deposition of Pd Schottky contacts on the defects observed in an irradiated n-type Si substrate. Deep-level transient spectroscopy (DLTS) was used in order to investigate the possible defects in Schottky diodes on the n-type Si. In this study the defects present where the diode was deposited first and then irradiated (“post irradiated”) were compared to those present where the substrate was irradiated first, and the Pd deposited after irradiation (“pre-irradiated”). In the post-irradiated material, the familiar radiation-induced defects were observed. However, in the pre-irradiated material, fourteen new defects were observed, with DLTS signatures differing from those of the defects in the post-irradiated diodes. The newly identified defects seemed to be specifically caused by the deposition of Pd contacts after irradiation of the substrate, as these defects were not observed when other metals such as Au, Ni, Al and Ag were deposited after irradiation. In this paper, we will refer to the observed effect that Pd deposition replaced the familiar radiation-induced defects in Si with the new set of defects as the “Pd effect”. Careful experiments ruled out annealing due to inadvertent heating of the sample during deposition as a possible cause. Care was taken to avoid all sources of contamination: The effect was observed for different sources of Pd and crucibles. This effect was inhibited by the presence of a thin intermediate layer of Pd or Au deposited before irradiation. We therefore conclude that the effect is only observed when Pd is deposited directly onto the irradiated Si surface. Out of the fourteen newly observed defects, four defects, with activation energy of 182, 220, 360 and 607 meV, had DLTS signatures corresponding to those of defects previously observed in Pd-containing Si. For the rest of the defects, no defects with similar DLTS signatures were found in literature. We therefore believe that the defects observed are produced by defect enhanced diffusion of Pd. Overall, the study enhances our understanding of defect behaviour in silicon-based devices, particularly under irradiation and metal deposition conditions, and reveals the unique properties and effects of Pd.

Hydrogen Diffusion in the Lower Mantle Revealed by Machine Learning Potentials

AbstractHydrogen may be incorporated into nominally anhydrous minerals including bridgmanite and post‐perovskite as defects, making the Earth's deep mantle a potentially significant water reservoir. The diffusion of hydrogen and its contribution to the electrical conductivity in the lower mantle are rarely explored and remain largely unconstrained. Here we calculate hydrogen diffusivity in hydrous bridgmanite and post‐perovskite, using molecular dynamics simulations driven by machine learning potentials of ab initio quality. Our findings reveal that hydrogen diffusivity significantly increases with increasing temperature and decreasing pressure, and is considerably sensitive to hydrogen incorporation mechanism. Among the four defect mechanisms examined, (Mg + 2H)Si and (Al + H)Si show similar patterns and yield the highest hydrogen diffusivity. Hydrogen diffusion is generally faster in post‐perovskite than in bridgmanite, and these two phases exhibit distinct diffusion anisotropies. Overall, hydrogen diffusion is slow on geological time scales and may result in heterogeneous water distribution in the lower mantle. Additionally, the proton conductivity of bridgmanite for (Mg + 2H)Si and (Al + H)Si defects aligns with the same order of magnitude of lower mantle conductivity, suggesting that the water distribution in the lower mantle may be inferred by examining the heterogeneity of electrical conductivity.

Advances in fast 4H–SiC crystal growth and defect reduction by high-temperature gas-source method

This paper reviews recent progress in the development of high-speed 4H–SiC bulk crystal growth technology using the high-temperature gas-source method (high-temperature chemical vapor deposition). Vertical-type reactors capable of growing SiC bulk crystals of 50–75 and 100–150 mm in diameter have been developed, as have reactor configurations and growth conditions to achieve a high growth rate and material quality. Using the reactors, high growth rates up to or exceeding 3 mm/h have been achieved by employing an H2–SiH4–C3H8 gas system with high partial pressures of source gases and high growth temperature of 2500–2550 °C. It is also confirmed that the dislocation densities decline significantly in the direction of growth under proper growth conditions. Key factors for enhancing growth rate and improving crystal quality in the growth process are discussed.

Intrinsic defects in non-irradiated silicon carbide crystals

A comprehensive study of the intrinsic defects in sublimation-grown SiC crystals, depending on the growth conditions and thermal annealing is carried out. Complexes of the intrinsic defects including carbon vacancy (VC) and impurities atoms are found in the Si-rich SiC crystals grown by physical vapor transport at low temperatures below 2200 °C. Similar defects are also observed in the SiC crystals irradiated with high-energy particles. Intrinsic defects in grown SiC crystals are characterized by high thermal stability, which is associated with the presence of active metastable clusters. Experimental evidence for the presence of the active clusters in the wide temperature range (up to 2600 °C) is presented. It is shown that intrinsic defects can be also introduced in the SiC crystal by high-temperature diffusion from the p-type epitaxial layer. Paramagnetic defects in SiC are considered a material platform for sensing, quantum photonics, and information processing at ambient conditions.

Formation of E-band luminescence-active centers in bismuth-doped silica fiber via atomic layer deposition.

In this study, a Si defect structure was added into the silica network in order to activate the bismuth and silica structure active center. TD-DFT theoretical simulations show that the Bi and Si ODC(I) models can excite the active center of the E-band at 1408 nm. Additionally, the Bi-doped silica fiber (BDSF) with improved fluorescence was fabricated using atomic layer deposition (ALD) combined with the modified chemical vapor deposition (MCVD) technique. Some tests were used to investigate the structural and optical properties of BDSF. The UV-VIS spectral peak of the BDSF preform is 424 cm-1, and the binding energy of XPS is 439.3 eV, indicating the presence of Bi° atom in BDSF. The Raman peak near 811 cm-1 corresponds to the Bi-O bond. The Si POL defect lacks a Bi-O structure, and the reason for the absence of simulated active center from the E-band is explained. A fluorescence spectrometer was used to analyze the emission peak of a BDSF at 1420 nm. The gain of the BDSF based optical amplifier was measured 28.8 dB at 1420 nm and confirmed the effective stimulation of the bismuth active center in the E-band.

Crater-free monolayer graphene above the 2D Si film on SiC(0001) formed via SiSn cointercalation and Sn deintercalation

When Si atoms are intercalated under the graphene-like zero layer (ZL) generated on the SiC(0001) substrate, the resulting quasi-free-standing monolayer graphene (QFMLG) has lots of crater-like defects due to a strong Si-C reaction. Here, a method for creating crater-free QFMLG above a two-dimensional Si film is investigated using scanning tunneling microscopy and photoemission spectroscopy. The method involves forming a SiSn interfacial film as a precursor via cointercalation performed by sequential Sn and Si deposition on the ZL at room temperature and annealing at 650–700 °C. The Sn atoms prevent reactive Si atoms from directly contacting the ZL, which would otherwise cause SiC defects. The sample is then annealed at 750 °C to selectively remove the Sn atoms from the SiSn interfacial film, leaving a well-ordered Si film. The SiSn film composed of a bottom Si layer and top Sn atoms has a short-range-ordered “2 × 2” or a long-range-ordered 2×7 superstructure depending on the annealing temperature and the Sn coverage. Both the superstructures are semiconducting and induce less n-doped QFMLG than the pure Si film.

Dislocations in Crystalline Silicon Solar Cells

Dislocation is a common extended defect in crystalline silicon solar cells, which affects the recombination characteristics of solar cells by forming deep‐level defect states in the silicon bandgap, thereby reducing the lifetime of minority carrier. Hence, reducing the impact of defects on device performance is an effective strategy to optimize the performance of photovoltaic devices. This article reviews the observation and engineering of dislocation in Si solar cell. The structure and deformation of Si can be directly observed by chemical etching combined with electron microscopy. Also, more information about dislocation is obtained indirectly by monitoring the electrical and optical properties of Si. The classification, density, distribution of dislocations, and their interactions with other defects in Si can affect the lifetime of minority carriers and thereby reduce the performance of Si solar cells. In order to achieve higher cell efficiency, crystals with less or even no dislocation should be obtained. In addition to the specification of controlling the relevant parameters during the growth of silicon ingots to obtain the minimum dislocation density, it is necessary to study the behavior of dislocation in Si wafers under the combined action of external stress, temperature, and other defects.

Adsorption of gas molecules on intrinsic and defective MoSi2N4 monolayer: Gas sensing and functionalization

The adsorption behaviors of CO, NH3, NO, and NO2 on intrinsic and defective MoSi2N4 monolayer, and the electronic properties, magnetic and gas sensing properties are researched by first-principles calculations. The low adsorption energies of gas molecules adsorbed on the intrinsic MoSi2N4 systems demonstrate that physisorption characteristics. The CO and NH3 adsorbed on MoSi2N4 systems exhibit non-magnetic semiconductor behavior, whereas the NO and NO2 adsorbed on MoSi2N4 systems emerge magnetic semiconductor behavior. The recovery time of the CO, NH3, NO, and NO2 adsorbed on MoSi2N4 systems is 1.70 × 10−11, 3.6 × 10−10, 2.60 × 10−11, and 3.21 × 10−10 s, respectively. Meanwhile, the sensitivities are 0.42 (CO), 0.41 (NH3), 0.51 (NO), and 0.27 (NO2) for the intrinsic MoSi2N4, respectively, demonstrating that MoSi2N4 can be an invertible sensor to detect CO, NH3, NO, and NO2 in the environment. Interestingly, the N defect MoSi2N4(VN/MoSi2N4) system displays magnetic semiconductor features, while the NO adsorbed VN/MoSi2N4 system has non-magnetic semiconductor feature. The Si defect MoSi2N4 (VSi/MoSi2N4) system appears magnetic semimetal characteristics, while the NH3 adsorbed VSi/MoSi2N4 system appears nonmagnetic semiconductor characteristics. Compared with the intrinsic MoSi2N4, the defect MoSi2N4 adsorption systems has stronger adsorption energy, suggesting that the stronger capture ability of the defect MoSi2N4 for CO, NH3, NO, and NO2.

Sr–Si diagram at Si contents of 55–100 at% and crystal structure of SrSi2-x

Cubic SrSi2 has attracted attention as a thermoelectric material or Weyl semimetal candidate material. However, its physical properties have not been examined in detail. High-quality samples are required for this purpose. A previous study on the Sr–Si phase diagram reported that cubic SrSi2 is a low-temperature phase and tetragonal SrSi2 is a high-temperature phase based on little experimental evidence, highlighting the difficulty in synthesizing high-quality cubic SrSi2 samples. Therefore, a new investigation of the Sr–Si phase diagram is necessary. This study experimentally investigated the Sr–Si diagram at Si contents of 55–100 at% using arc-melted samples by performing inductively-coupled plasma optical emission spectroscopy, electron-probe microanalysis, powder X-ray diffraction analysis, and differential thermal analysis. Two intermetallic compounds (SrSi2-x and SrSi2) and two eutectic reactions existed in this Si content range. The eutectic points were approximately 57 at% and 1053.2 °C for Liquid⇔SrSi + SrSi2-x and approximately 75 at% and 1050.0 °C for Liquid ⇔SrSi2 + Si. SrSi2 had no high-temperature phase and melted congruently at 1121 °C. SrSi2-x existed at Si contents of 62.4–65.0 at%, and it is formed by the peritectic reaction Liquid + SrSi2⇔ SrSi2-x. SrSi2-x crystallized into a monoclinic variant of the √5 × √5 × 1 α-ThSi2-type superstructure with ordered Si defects at the body-center position of the cell (space group: I121, No. 5). SrSi2-x is the first example of the α-ThSi2-type superstructure.

Effects of vacancy and external electric field on the electronic properties of the MoSi2N4/graphene heterostructure

Recently, the newly synthesized septuple-atomic layer two-dimensional (2D) material MoSi2N4 (MSN) has attracted attention worldwide. Our work delves into the effect of vacancies and external electric fields on the electronic properties of the MSN/graphene (Gr) heterostructure using first-principles calculation. We find that four types of defective structures, N-in, N-out, Si and Mo vacancy defects of monolayer MSN and MSN/Gr heterostructure are stable in air. Moreover, vacancy defects can effectively modulate the charge transfer at the interface of the MSN/Gr heterostructure as well as the work function of the pristine monolayer MSN and MSN/Gr heterostructure. Finally, the application of an external electric field enables the dynamic switching between n-type and p-type Schottky contacts. Our work may offer the possibility of exceeding the capabilities of conventional Schottky diodes based on MSN/Gr heterostructures.

Preparation of thin-film SOI wafer by low-dose ion implantation

Silicon-on-insulator (SOI) devices have many advantages, such as high speed, low energy consumption, radiation-hard, and high integration. In this paper, the separation by implanted oxygen process under low-dose implantation conditions is studied by the two-step implantation method combined with the internal thermal oxidation process. The effects of different types of silicon wafers and different implantation doses on SOI surface defects, top Si thickness, buried oxide (BOX) layer thickness, BOX layer breakdown voltage, and top Si defect density were investigated. Ultra-thin SOI wafers are prepared by epitaxial silicon wafers and control the first implantation dose. The number of surface defects of SOI materials is less than 100 counts, the breakdown voltage of the BOX layer is about 7.8 MV/cm, and the top Si dislocation density is about 8 × 103 cm−2.

Raman studies in Al+ implanted semi insulating 6H-SiC

Depth-resolved Raman spectroscopy study of semi-insulating (SI) 6H-Silicon Carbide (SI:6H-SiC) implanted with Al+ of three ion fluencies at 400 keV and re-crystallization upon annealing at 800 °C are presented. Deformations related to SiC bond breakages and defect recovery were investigated from the Raman first-order acoustical and second-order optical phonon modes. Annealing effected the asymmetrical to symmetrical Raman peaks and the regaining of active Raman modes. Raman Z- scan studies exhibited an amorphous broad feature in the near-surface and partial recovery in the deep region of the high fluence annealed sample indicating the defects' agglomeration and recrystallization.