Si Interstitials Research Articles

Theoretical study of hydrogen impact on concentration of intrinsic point defects during Czochralski Si crystal growth

Control of intrinsic point defects (vacancy V and interstitial Si I) at the atomic level is required for Si substrates to satisfy the performance demands of the latest semiconductor devices. Sugimura et al. (2014) recently reported that doping hydrogen (H) atoms during Czochralski Si crystal growth affects the point defect behavior in two ways: (i) Si crystal becomes more V rich and (ii) the formation of dislocation clusters is suppressed. The finding of (ii) suggests that H-doping is a promising technique for the mass production of Si substrates used for power devices, among other applications. However, the effect of H-doping on point defect behavior during Si crystal growth is not yet fully understood. The purpose of the present study is to clarify the finding of (i). We performed first principles calculation of the formation energy and formation (vibration) entropy of V and I in the area influenced by the H atom in supercells composed of 64 and 216 Si atoms and then obtained the concentration of point defects incorporated at the melt/solid interface on the basis of the results. Our main findings are as follows. (1) There are three structures of hydrogen-vacancy complex (H-V) where the V formation energy remarkably decreases and four structures of hydrogen-interstitial Si complex (H-I) where the I formation energy remarkably decreases. (2) The H impact on V concentration is larger than that on I concentration and becomes apparent when H concentration is higher than 1015/cm3. (3) The experimental finding of H impact on the concentration of intrinsic point defects is explained quantitatively.

Low-energy cross-sectional cathodoluminescence analysis of the depth distribution of point defects in Si-ion-implanted β-Ga2O3

Low-energy cross-sectional cathodoluminescence (CL) with a beam energy of 1 keV was applied to Si-ion-implanted β-Ga2O3 (−201) wafers to investigate implantation damage and recovery. The semi-quantitative CL-intensity depth profiles were obtained by considering nonradiative recombination at the surface. We found that the CL intensity did not fully recover, even after annealing at 1273 K. Such insufficient recovery was prominent in the Si-diffusion region, suggesting that Si-dopant activation and Si diffusion are strongly correlated through interaction with point defects generated by implantation, such as Si interstitials and Ga vacancies.

Origin of carrier lifetime degradation in floating-zone silicon during a high-temperature process for insulated gate bipolar transistor

We report on the relationship between carrier lifetime degradation of floating-zone silicon (FZ Si) and the guard ring formation process for silicon integrated gate bipolar transistor (Si-IGBT). A clear carrier lifetime degradation was observed through the guard ring oxidation and annealing processes for Si-IGBT and showed interstitial oxygen (Oi) concentration dependence, which was obtained by Fourier transform infrared absorption spectroscopy. Based on the carrier lifetime measurements through the step etching of the FZ Si substrate, it has been suggested that the carrier lifetime degradation is not only caused by the Oi itself near the FZ Si surface region but also the other defects induced by the Oi injection. Diffused interstitial Si atoms kicked-out by the Oi into the FZ Si substrate, which has a longer diffusion length than Oi, can be considered to be the origin of the carrier lifetime degradation.

Ultra-slow dynamic annealing of neutron-induced defects in n-type silicon: role of charge carriers

Neutron bombardments with equivalent fluence (1$\times$10$^{10}$ cm$^{-2}$) and different fluxes ($2.5\times$10$^5$ cm$^{-2}$s$^{-1}$ to $1\times$10$^7$ cm$^{-2}$s$^{-1}$) have been performed on three kinds of bipolar devices with n-type silicon as active regions. The measured increase of base currents and input bias currents are found to decrease with increasing neutron flux, implying that the strength of the dynamic annealing of divacancy defects in n-type silicon follows a positive flux dependence. Such a flux dependence is the same as that observed in ions implantation using protons, but the evident flux sensitivity in our experiment is 4 orders of magnitude lower than that of proton bombardment, despite the similarity in the masses and energies of the two particles. The huge discrepancy of flux range is attributed to the presence of vast charge carriers in proton bombardments, which strongly accelerate the dynamic annealing of defects by enhancing the diffusion velocity of Si interstitials and dissociation rate of defect clusters. Our work would contribute to the understanding of the defect annealing processes in silicon.

Theoretical distributions of point-defect concentration in a Si ingot grown inside a melt using the noncontact crucible method considering the accumulation effect of diffusion flux

The noncontact crucible (NOC) method has a large and deep low-temperature region in the upper central part of a Si melt to grow a uniform large Si single ingot without contact with the crucible wall. The temperature distribution in the NOC ingot is quite different to that in an ingot grown by the Czochralski (CZ) method because the NOC ingot is grown inside the Si melt. However, the distributions of point defects such as vacancy and interstitial Si atom are not known for the NOC ingot. To clarify the distributions of point defects, a simulation model is proposed to calculate the distribution of point defects in the NOC ingot. The effect of accumulation of diffusion fluxes on the concentrations of both vacancy and interstitial Si atom is considered for NOC growth because these diffusion fluxes are expected to continuously affect such concentrations in the ingot grown with the moving interface under the relatively low temperature gradient inside the melt. This point is one of the large merits of NOC growth. The concentrations of vacancy and interstitial Si atom were also calculated after the dynamic equilibrium pair-annihilation process between the diffused point defects during growth. They were calculated as a function of distance from the growing interface. By selecting the growth conditions, the concentrations of vacancy and interstitial Si atom were found to be very close to each other all over the ingot. The cross point where the concentrations of vacancy and interstitial Si atom were the same was found to strongly depend on G, the temperature gradient in the crystal.

Effects of point defects on oxidation of 3C–SiC

The influence of implantation-induced point defects (PDs) on SiC oxidation is investigated via molecular dynamics simulations. PDs generally increase the oxidation rate of crystalline grains. Particularly, accelerations caused by Si antisites and vacancies are comparable, and followed by Si interstitials, which are higher than those by C antisites and C interstitials. However, in the grain boundary (GB) region, defect contribution to oxidation is more complex, with C antisites decelerating oxidation. The underlying reason is the formation of a C-rich region along the oxygen diffusion pathway that blocks the access of O to Si and thus reduces the oxidation rate, as compared to the oxidation along a GB without defects.

Dislocation sink annihilating threading dislocations in strain-relaxed Si1−xGex layer

We proposed a dislocation sink technology for achieving Si1−xGex multi-bridge-channel field-effect-transistor beyond 5 nm transistor design-rule that essentially needs an almost crystalline-defect-free Si1−xGex channel. A generation of a dislocation sink via H+ implantations in a strain-relaxed Si0.7Ge0.3 layer grown on a Si substrate and a following annealing almost annihilate completely misfit and threading dislocations located near the interface between a relaxed Si0.7Ge0.3 layer and a Si substrate. A real-time (continuous heating from room temperature to 600 °C) in situ high-resolution-transmission-electron-microscopy and inverse-fast-Fourier-transform image observation at 1.25 MV acceleration voltage obviously demonstrated the annihilation process between dislocation sinks and remaining misfit and threading dislocations during a thermal annealing, called the [SiI or GeI + VSi or VGe → Si1−xGex] annihilation process, where SiI, GeI, VSi, and VGe are interstitial Si, interstitial Ge, Si vacancy, and Ge vacancy, respectively. In particular, the annihilation process efficiency greatly depended on the dose of H+ implantation and annealing temperature; i.e. a maximum annihilation process efficiency achieved at 5 × 1015 atoms cm−2 and 800 °C.

Effects of Si concentration on electronic structure and optical gap of Si-doped β-Ga2O3

The electronic structures and the optical gaps of Si-doped β-Ga2O3 with different Si concentration are studied by the generalized gradient approximation combined Hubbard U (GGA + U) method based on the density functional theory. The doping formation energy reveals that Si-doped β-Ga2O3 is mainly realized in the form of substitutional Si rather than interstitial Si, and tends to obtain effective doping under O-poor condition. As substitutional Si concentration increases, the optical gap of Si-doped β-Ga2O3 increases while the bandgap narrows, which are mainly attributed to the Burstein-Moss effect and the many-body renormalization effect. The bandgap widening ΔEBM and the bandgap narrowing ΔEBGN of Si-doped β-Ga2O3 as a function of Si carrier concentration can be described by Pisarkiewicz’s model and Schmid’s empirical expression, respectively.

Електронні характеристики квантових точок СdS, що містять дефекти

Using the density functional theory and the generalized gradient approximation, we calculated the atomic structure, the density of electronic states, and the optical absorption spectra of CdS quantum dots containing intrinsic defects — a cadmium vacancy VCd and an interstitial sulfur atom SI, and substitutional impurities — zinc and copper in place of the atom cadmium — ZnCd and CuCd, respectively. The calculations were performed for the Cd33S33 cluster corresponding to the so-called “magic” size of the quantum dot. This size has a minimum of dangling bonds at the surface and allows the using of such a cluster without the passivation. The structural relaxation during the formation of such defects and the distribution of the wave function of the state corresponding to the top of the valence band are analyzed in details. It has been shown that the cadmium vacancy forms local states in the band gap of CdS nanocrystals, and can serve as centers of radiative recombination. Other defects form energy levels in the depths of the valence band or near its top, but whose energy positions do not correspond to the band maxima in the experimental photoluminescence spectra of CdS quantum dots, both undoped and doped with zinc. The calculated optical absorption spectra demonstrate a strong peak in the region of fundamental absorption of CdS for a cluster containing a substitutional impurity of CuCd, in contrast to other systems where no such peaks are observed. In addition, the replacement of the cadmium atom with copper leads to a decrease in the number of chemical bonds to three and, accordingly, to the largest relaxation among the systems studied. This feature is caused by the crystal structure inhomogeneity of copper sulfide CuxS, which, depending on stoichiometry, can be either a semiconductor or a metal.

First-principles study of pressure and SiO-incorporation effect on dynamical properties of silicon oxide

The pressure and SiO-incorporation effect on the temperature dependence of dynamical properties for silicon oxide (SiO2)1−x(SiO)x is theoretically studied by first-principles molecular dynamics. It is found that the incorporation of SiO enhances the selfdiffusions even under high pressure. The SiO effect on Si selfdiffusion is however reduced by the pressure at temperature lower than 4000 K, and the amount of reduction is larger for lower temperature, while the effect on O selfdiffusion is hardly reduced, being independent of the temperature. Such a difference is thought to come from the difference in selfdiffusion mechanisms between Si and O. It is indicated that the incorporated SiO acts as combined SiO interstitials rather than separate Si interstitials or O vacancies. This also suggests that the oxide viscous flow mechanism is a promising candidate for the origin of the Si missing in oxidizing Si nanopillars.

Influence of helium on the nucleation and growth of bubbles in silicon: a multiscale modelling study

The formation and growth of helium-filled cavities in silicon have been investigated using both molecular dynamics simulations and rate equation cluster dynamics calculations. This multiscale approach allowed us to identify atomic scale mechanisms involved in nucleation and early growth steps, and to follow their dynamics over experimental timescales. We especially focus our analyses on the influence of helium. Our results first suggest that both Ostwald ripening and migration-coalescence mechanisms are jointly activated during bubble growth. We also discover that an original mechanism, based on the splitting of bubbles, could have a significant contribution. Overall, helium atoms are found to delay growth, proportionally to their concentration. This can be clearly observed at the nanosecond timescale. However, for longer timescales, cluster dynamics calculations also reveal periods of accelerated growth for specific helium concentrations. Finally, it is determined that the main effect of Si interstitials is to impede bubble growth, due to an early recombination with vacancies.

The role of annealing ambient on diffusion of implanted Si in β-Ga2O3

The most common n-type dopant, Si, was implanted into bulk (-201) β-Ga2O3 at total doses from 2x1013-2x1015 cm-2 and annealed at 1100 °C for 10-120 secs in either O2 or N2 ambients. Secondary Ion Mass Spectrometry profiling showed a significant effect of the annealing ambient on the Si diffusivity. In the case of O2 annealing, there was extensive redistribution of the Si across the entire dose range, while in sharp contrast, the use of N2 annealing suppressed the Si diffusion. The results are consistent with a defect-assisted process. Excellent fits to the Si profiles were obtained with the FLOOPS simulator, assuming mobile vacancy/defect concentrations as the important factor for the difference in the O2 vs N2 annealing ambients. One possibility is that for N2 anneals, more Ga vacancies are created, enabling interstitial Si to migrate onto a substitutional Ga site where it has low diffusivity. The N2 ambient also suppresses loss of Si to the surface, with >90% of the initial dose retained after annealing at 1100 °C for 120 secs, compared to 66-77% with O2 anneals under the same conditions.

Study on interfacial interaction between Si and ZnO

The interfacial reaction and bonding mechanism of Si based undoped and Al-doped ZnO films were investigated experimentally and numerically. Si/ZnO heterojunctions were fabricated onto p-Si(100) wafers by RF magnetron sputtering, then the undoped and Al doped ZnO (AZO) films coated Si substrates were annealed in argon atmosphere (ZnO-Ar and AZO-Ar) and air atmosphere (ZnO-Air and AZO-Air) respectively. X-ray diffraction (XRD) and Fourier transform infrared spectra (FTIR) show the prepared Si-based films have wurtzite structure with (002) preferential growth, and demonstrate several Si oxides exist in both cases. X-ray photoelectron spectroscopy (XPS) finds that oxygen vacancies exist in ZnO-Ar, moreover, the stoichiometry between Zn and O in AZO-Ar film to be close to 1:1, and high oxygen content in ZnO-Air, which are also supported by Hall measurement. Furthermore, the Si 2p of XPS spectrum shows the width of interfacial interaction between Si and ZnO become weaker with the order of ZnO-Ar, AZO-Ar and ZnO-Air. To elucidate the joining and bonding mechanism between Si substrate and ZnO coating layer, molecular dynamics and first principle simulations were performed in this work, the simulation results show certain interstitial Si atoms coming from Si substrate interact with O atoms related to the Zn–O bonding at the Si/ZnO interface, and resulting in oxygen vacancies in ZnO film. The experiment and simulation show the interfacial interaction between Si and ZnO depends on oxygen content coming from ZnO coating layer, the limited oxygen coming from ZnO film could increase the width of Si/ZnO interfacial interaction and leave oxygen vacancies in ZnO film due to Si robbing O atoms related to Zn–O bonding.

Native point defects and carbon clusters in 4H-SiC: A hybrid functional study

We report first-principles calculations that clarify the formation energies and charge transition levels of native point defects and carbon clusters in the 4H polytype of silicon carbide (4H-SiC) under a carbon-rich condition. We applied a hybrid functional that reproduces the experimental bandgap of SiC well and offers reliable defect properties. For point defects, we investigated single vacancies, antisites, and interstitials of Si and C on relevant sites. For carbon clusters, we systematically introduced two additional C atoms into the perfect 4H-SiC lattice with and without removing Si atoms and performed structural optimization to identify stable defect configurations. We found that neutral Si antisites are energetically favorable among Si-point defects in a wide range of the Fermi level position around the intrinsic regime, whereas negatively-charged Si vacancies and a positively-charged Si interstitial on a site surrounded by six Si and four C atoms become favorable under n- and p-type conditions, respectively. For C-point defects, neutral C antisites are favorable under intrinsic and n-type conditions, whereas positively-charged C vacancies become favorable under p-type conditions. We also found that a di-carbon antisite is more favorable than a C-split interstitial, which is the most stable form of single C interstitials.

Heat and charge transport in bulk semiconductors with interstitial defects

Interstitial defects are inevitably present in doped semiconductors that enable modern-day electronic, optoelectronic or thermoelectric technologies. Understanding of stability of interstitials and their bonding mechanisms in the silicon lattice was accomplished only recently with the advent of first-principles modeling techniques, supported by powerful experimental methods. However, much less attention has been paid to the effect of different naturally occurring interstitials on the thermal and electrical properties of silicon. In this work, we present a systematic study of the variability of heat and charge transport properties of bulk silicon, in the presence of randomly distributed interstitial defects (Si, Ge, C and Li). We find through atomistic lattice dynamics and molecular dynamics modeling studies that, interstitial defects scatter heat-carrying phonons to suppress thermal transport-1.56% of randomly distributed Ge and Li interstitials reduce the thermal conductivity of silicon by $\sim$ 30 and 34 times, respectively. Using first principles density functional theory and semi-classical Boltzmann transport theory, we compute electronic transport coefficients of bulk Si with 1.56% Ge, C, Si and Li interstitials, in hexagonal, tetrahedral, split-interstitial and bond-centered sites. We demonstrate that hexagonal-Si and hexagonal-Ge interstitials minimally impact charge transport. To complete the study, we predict the thermoelectric property of an experimentally realizable bulk Si sample that contains Ge interstitials in different symmetry sites. Our research establishes a direct relationship between the variability of structures dictated by fabrication processes and heat and charge transport properties of silicon. The relationship provides guidance to accurately estimate performance of Si-based materials for various technological applications.

Self-Organized Ge Nanospherical Gate/SiO2/Si0.15Ge0.85–Nanosheet n-FETs Featuring High ON-OFF Drain Current Ratio

We reported experimental fabrication and characterization of Si0.15Ge0.85 n-MOSFETs comprising a gate-stacking heterostructure of Ge-nanospherical gate/SiO2/Si0.15Ge0.85-nanosheet on SOI (100) substrate in a self-organization approach. This unique gate-stacking heterostructure is simultaneously produced in a single oxidation step as a consequence of an exquisitely controlled dynamic balance between the concentrations of oxygen, Si, and Ge interstitials at 900 °C. Process-controlled tunability of nanospherical gate of 60–100 nm in diameter, gate oxide thickness of 3 nm, and Si0.15Ge0.85 nanosheet with compressive strain of −2.5% was achieved. Superior gate modulation is evidenced by subthreshold slope of 150 mV/dec and ${I} _{\mathrm{ ON}}/{I} _{\mathrm{ OFF}}>5\times 10^{8}$ ( ${I} _{\mathrm{ OFF}} and ${I} _{\mathrm{ ON}}>500~\mu \text{A}/\mu \text{m}$ ) measured at $V_{G}= +1V$ , $V_{D} = +1$ V, and $T = 80$ K for our device with channel length of 75 nm.

Density functional theory calculations of self- and Xe diffusion in U3Si2

Uranium silicide, U3Si2, has been proposed as an advanced nuclear fuel to be used in light water reactors (LWRs). Development of this alternative to the predominant current fuel, UO2, is motivated by enhanced accident tolerance as a result of higher thermal conductivity as well as improved fuel cycle economics through increased uranium density. In order to accurately model the fuel performance of U3Si2, the diffusion rate of point defects, which is related to self-diffusion, and of fission gas atoms must be determined. DFT calculations are used to predict the U and Si point defect concentrations, the corresponding self-diffusivities, the preferred Xe trap site and the Xe diffusivity. Effects of irradiation are not considered. A low defect formation energy and a high entropy for Si interstitials give rise to Si-rich non-stoichiometry at elevated temperatures. Both U and Si self-diffusion and Xe diffusion are anisotropic as a consequence of the tetragonal crystal structure of U3Si2. Si diffusion occurs by interstitial mechanisms in both the a-b plane and along the c axis, while the U c axis diffusion rate is controlled by a vacancy mechanism. Interstitial diffusion of U is very fast in the a-b plane of the U3Si2 crystal structure. Xe atoms prefer to occupy U vacancy trap sites. The highest Xe diffusion rate occurs by a vacancy mechanism in both the a-b plane and along the c axis. The diffusion rate is similar in the a-b plane and along the c axis. U and Si self-diffusion and Xe diffusion are all faster in U3Si2 than intrinsic U and Xe diffusion in conventional UO2 nuclear fuel.

Molecular dynamics investigation of grain boundaries and surfaces in U3Si2

Uranium-silicide (U-Si) fuels are being pursued as a possible accident tolerant fuel (ATF). This uranium alloy benefits from higher thermal conductivity and higher fissile density compared to uranium dioxide (UO2). In order to perform engineering scale nuclear fuel performance simulations, the material properties of the fuel must be known. Currently, the experimental data available for U-Si fuels is rather limited. Thus, multi-scale modeling efforts are underway to address this gap in knowledge. Interfaces play a critical role in the microstructural evolution of nuclear fuel under irradiation, acting both as sinks for point defects and as preferential nucleation sites for fission gas bubbles. In this study, a semi-empirical modified Embedded-Atom Method (MEAM) potential is utilized to investigate grain boundaries and free surfaces in U3Si2. The interfacial energy as a function of temperature is investigated for ten symmetric tilt grain boundaries, eight unique free surfaces and voids of radius up to 35 Å. The point defect segregation energy for both U and Si interstitials and vacancies is also determined for two grain boundary orientations. Finally, the entropy change and free energy change for grain boundaries is calculated as a function of temperature. This is the first study into grain boundary properties of U-Si nuclear fuel.

Effect of carbon on boron diffusion and clustering in silicon: Temperature dependence study

Atom probe tomography and secondary ion mass spectrometry were used to investigate the effects of carbon (C) co-implantation and subsequent annealing at 600 to 1200 °C on the behavior of implanted boron (B) atoms in silicon. When B alone was implanted, annealing at 600 to 800 °C caused it to form clusters in the peak region (1020 cm−3) of the concentration profile, and diffusion only occurred in the low-concentration tail region (<1018 cm−3), which is thought to be the well-known transient enhanced diffusion. However, when co-implantation with C was performed, this diffusion was almost completely suppressed in the same annealing temperature range. In the absence of C implantation, annealing at 1000 °C caused B clusters to begin to dissolve and B to diffuse out of the peak concentration region. However, this diffusion was also suppressed by C implantation because C atoms trapped B atoms in the kink region found at the B concentration level of 2 × 1019 cm−3. At 1200 °C, B clusters were totally dissolved and a strong B diffusion occurred. In contrast to lower annealing temperatures, this diffusion was actually enhanced by C implantation. It is believed that Si interstitials play an important role in the interaction between B and C. This kind of comprehensive investigation yields important information for optimizing ion implantation and annealing processes.

Elastic Moduli and Elastic Constants of Alloy AuCuSi With FCC Structure Under Pressure

Abstract This paper studies on the dependence of the mean nearest neighbor distance, the Young modulus E, the bulk modulus K, the rigidity modulus G and the elastic constants C 11, C 12, C 44 on temperature, pressure, the concentration of substitution atoms and the concentration of interstitial atoms for alloy AuCuSi (substitution alloy AuCu with interstitial atom Si) with FCC structure by the way of the statistical moment method (SMM). The numerical results for alloy AuCuSi are compared with the numerical results for main metal Au, substitution alloy AuCu, interstitial alloy AuSi, other calculated results and experiments.