Interstitial Si Atoms Research Articles

Importance of zero cross-point (Cp = 0) control between the vacancy and interstitial Si atom concentration curves to obtain a perfect Si ingot using Si melt growth

The cross-point (Cp), which appears in the vacancy (CV) and interstitial Si atom (CI) concentration curves, is a simple controlling factor for ingot growth and provides a final goal to obtain a defect-free Si ingot using general Si melt growth. The importance of Cp is demonstrated using the noncontact crucible method (NOC), which has a relatively small temperature gradient due to an ingot grown inside the melt. The control of temperature gradient G at a constant growth rate v is simple for the actual ingot growth; thus, the present simulated results are expressed by G at a constant v. The concentration at the Cp point becomes smaller as G becomes smaller and finally becomes zero (Cp = 0), in which CV and CI are practically zero (CV=CI=0). The estimated G and temperature T at Cp = 0 for v = 0.000144 cm s−1 are 6.3, 12.5, and 18.5 K cm−1 and 1216 K (943 °C), 1354 K (1081 °C), and 1371 K (1098 °C), corresponding to each combination. At 1216 K, G should be precisely controlled within 6.3 ± 3 % K cm−1 in the region substantially close to Cp = 0 to maintain the remaining concentration of point defects substantially lower than 1.0 × 1013 cm−3. G should be changed during growth from larger G to smaller G, such as 6.3 K cm−1, to efficiently grow the ingot within the limited time. The changing point, x of G, is an important key parameter for the timing variation, where x denotes the normalized distance from the growing interface. The initial G is large; thus, the changing point of G approaches the growing interface. The growth condition necessary to obtain a defect-free Si ingot can be demonstrated using the Cp = 0 point, which is fully compatible with the perfect critical point where CV and CI are practically zero. The present results are mainly considered using the CV and CI concentration curves. However, these results largely help understand the approximate trend of G and v for the growth of defect-free ingot and the relation between Cp and the commonly used critical point between CV and CI.

Energetics of silicon in the bulk and near surfaces of tungsten: a first-principles study

Siliconization of the tokamak walls is a candidate method to improve plasma confinement in fusion tokamaks containing tungsten plasma facing components (W PFCs). To understand the interactions of silicon (Si) with W, the Si behavior in bulk W, and near three low-index W surfaces ((100), (110) and (111)) has been investigated using first-principles density functional theory. In bulk W, Si interstitial atoms have a low solution ability and high mobility, and Si atoms can be strongly trapped by W vacancies. The interaction between two Si adatoms is responsible for the stability of adatom superstructures on W surfaces, consistent with previous experimental observation (Tsong and Casanova 1981 Phys. Rev. Lett. 47 113). Although the coverage dependence of Si adsorption and diffusion energetics on surfaces is related to surface orientation, the W(110) surface has lower Si adsorption affinity and higher Si diffusivity than either the W(111) or W(100) surfaces. The most stable Si adatom superstructure on W surfaces is: square c(2 × 2) pattern on W(100) covered with 0.5 ML Si; rectangular c(4 × 2) pattern on W(110) with 0.25 ML Si; and rhombus p(1 × 1) pattern on W(111) with 1 ML Si. The coverage dependence of Si mobility on/toward W surfaces is generally related to the stability of the Si superstructures as a function of coverage on each surface. Interestingly, Si adatoms prefer to transport below the surface and into W subsurface by an exchange mechanism with W atoms, indicating the likelihood of epitaxial growth of W silicide layers on W surfaces during the operation of W PFCs.

Effects of hydrogen on trap neutralization in BaSi2 with interstitial silicon atoms

Semiconducting barium disilicide (BaSi2) is one of emerging materials for solar cell applications. Therefore, defect neutralization is very important for improving its solar cell performance. Herein, the effect of atomic hydrogen (H) on the photoresponsivity of 500-nm-thick undoped n-BaSi2 films grown under Si-rich conditions by molecular beam epitaxy was examined, wherein interstitial Si atoms were likely to exist instead of common Si vacancies. The photoresponsivity reached a maximum of ∼1.3 A W−1 at room temperature (about twice as large as that for as-grown films) in BaSi2 films exposed to an atomic H for 10 s. This H treatment time is much smaller than that for BaSi2 films grown under stoichiometric conditions, indicating that interstitial Si atoms provide a smaller trap concentration with respect to the case of Si vacancy domination and incorporation of H atom can neutralize traps. The inverse logarithmic slope (E0) of the Urbach tail was investigated to discuss the dependence of the photoresponsivity of BaSi2 films on H treatment time. There was a clear negative correlation between E0 and photocurrent density obtained from the photoresponsivity. The detailed picture on how interstitial Si atoms affect the electronic structure of BaSi2 by defect state formation and how H atom incorporation modifies the structure is revealed by ab initio calculations that allowed interpreting and understanding of all experimentally observed trends.

Two-dimensional BMD, BSF, ring-OISF and COP distributions in a dislocation-free ingot grown by the NOC method

The noncontact crucible (NOC) method has a large and deep low-temperature region in Si melt to grow a uniform large Si single ingot. The theoretical simulation pointed out that the lowest vacancy or interstitial Si atom area appears in the region with the smaller ratio between temperature gradients at melt surface and growing interface. The growth condition to obtain this region is suitable for the NOC method. The quality of a NOC ingot was first evaluated by determining the distribution of bulk micro defect (BMD), bulk stacking fault (BSF), oxidation induced stacking fault (OISF) and crystal originated particle (COP) in the cross section of the dislocation-free ingot. A ring-OISF or BSF can be clearly observed on the cross section cut from the middle and tail parts of the ingot. BMD can be observed inside and outside the ring-OISF. By estimated comparison to the none-doping case, CV (=CI) at cross point clearly has a trend to increase for the high B-doing case (5 × 1019 cm−3), where CV and CI are concentration of vacancy and interstitial Si atom, respectively. Nevertheless, in comparison with the distribution of COP in Cz and NOC ingots, COP cannot be detected inside the ring-OISF in the NOC wafer under the same etching process as many COP can be observed in the Cz wafer. This may be a unique feature for NOC growth.

Two-dimensional distribution of vacancy concentration at cross points for the ingot length and the temperature gradients to largely reduce point defects and the growth of a dislocation-free NOC ingot for evaluation of its quality

The noncontact crucible (NOC) method has a large and deep low-temperature region in Si melt to grow a uniform large Si single ingot. The cross point with the same concentration of vacancy (CV) and interstitial Si atom (CI) is very important to reduce the point defects in NOC ingot. The relation between the temperature gradient, G, the position and concentration of cross point was estimated using equations derived from Voronkov’ explanation. For NOC growth, two stages for temperature gradient are required as G1 at the growing interface and G2 at the melt surface. The linear T profile is useful for the two-stage growth. Concentration curve of vacancy and interstitial Si atom was calculated on the two stages as a function of the distance from the growing interface. A cross point appears above the melt surface even for the two-stage calculation with a long ingot inside the melt. By the two dimensional-distribution of CV at cross point for G2/G1 and d1, CV has a tendency to become higher as G2/G1 becomes larger. On the whole, the higher CV area appears in the larger G2/G1 and shorter d1 region, and the lower CV area appears in the smaller G2/G1 and longer d1 region. The latter condition is suitable for the NOC growth. Such trend of CV at cross points should be utilized to reduce the remained point defects in ingot. Lower CV and CI at the cross point can reduce the remained point defects in a NOC ingot using smaller G2/G1, smaller G1 and longer d1 near the critical point. To confirm the quality of NOC ingot grown using the present method, a dislocation-free Si single ingot was grown utilizing silica crucibles by the NOC growth method. The maximum diameter and total length of the grown ingot are 17.5 and 15.5 cm, respectively. A Si ingot was experimentally grown by the NOC method. The bottom of the NOC ingot had a convex shape in the growth direction which is very advantageous to NOC growth.It was confirmed by habit lines and etch-pit density of dislocation whether the ingot was dislocation-free or not. A dislocation-free Si single ingot was realized by the NOC method for the first time.

In Situ Transmission Electron Microscopy Study of Shrinkage Kinetics of CH4N-Molecular-Ion-Implantation-Induced Extended Defects

The thermal stability of end-of-range (EOR) defects formed in a CH4N-molecular-ion-implanted epitaxial silicon (Si) wafer was studied by transmission electron microscopy (TEM) observation. By plan-view TEM observation, we found that the density and size of the CH4N-ion-implantation-induced EOR defects negligibly changed upon heat treatment at temperatures below 1000 °C, whereas the EOR defect density was drastically reduced by heating at 1100 °C. This result suggests that almost all CH4N-ion-implantation-induced EOR defects were sufficiently thermally stable to maintain their size at temperatures below 1000 °C, and that above 1100 °C, most of the EOR defects lost their stability, shrank and finally dissolved. Additionally, by in situ cross-sectional TEM observation during heat treatment, we found a large difference in the shrinkage rates of the EOR defects between at the beginning of heat treatment and the last minute of just before defect disappearance. We found that the EOR defects began to gradually shrank at the beginning of heat treatment (1st stage), and then the shrinkage rate rapidly increased (2nd stage), finally resulting in the dissolution of the defects. The activation energies for the shrinkage of EOR defects in the 1st and 2nd stages (E D-1 and E D-2) were found to be 7.55 ± 1.03 and 4.57 ± 0.32 eV, respectively. The shrinkage behavior in the 1st stage is likely to be due to the thermally activated desorption of C and N species that segregated along the edge of an EOR defect. On the other hand, from the E D-2 value, the shrinkage behavior in the 2nd stage is deduced to be due to the desorption of interstitial Si atoms. These findings suggest that this two-stage shrinkage behavior is peculiar to the EOR defects formed in the CH4N-ion-implanted epitaxial Si wafer, and that the interaction between the EOR defect and the impurities segregated at the edge of the defect affects the thermal robustness of the molecular-ion-implantation-induced EOR defects.

Formation behavior of oxygen precipitates in silicon wafers subjected to ultra-high-temperature rapid thermal process

In this study, we investigated the formation behavior of oxygen precipitates in Si wafers after a rapid thermal process (RTP) at 1350 °C in an oxygen atmosphere through experiments and simulations. The oxygen precipitate density varied based on the temperature (750–950 °C) and duration (0.5–16 h) of the first step of the two-step heat treatment after RTP. The highest oxygen precipitate density was achieved when the first-step temperature was set to 850 °C, and the second-step temperature was fixed at 1000 °C. The simulation consisted of the calculation of the depth profiles of the residual vacancy concentrations after RTP and oxygen precipitation during the two-step heat treatment after RTP. An empirical formula, in which the nucleation rate of the oxygen precipitates was assumed to be proportional to the fourth power of the residual vacancy concentration, was used in the temperature range of 600–1000 °C. In addition, we assumed that interstitial Si atoms, which were generated by the growth of the oxygen precipitates, consumed the residual vacancies through pair annihilation, thus stopping oxygen precipitation owing to the depletion of the residual vacancies. The simulation effectively reproduced the variations in the oxygen precipitate densities under different conditions in the first step of the heat treatment. Considering the results of the simulation, we concluded that the resulting oxygen precipitate density was determined by the nucleation rate, growth size, and timing of the terminal point of the nucleation.

Molecular dynamics study of effects of point defects on thermal conductivity in cubic silicon carbide

Silicon carbide (SiC) has been widely used in nuclear technology due to its excellent properties. In the irradiation environment, the energetic incident particles can cause the atoms in the material to deviate from the position of the crystal lattice, thereby producing the vacancies, interstitial atoms, anti-site atoms and other point defects. These defects will change the thermal properties of the material and degrade the service performance of the material. Therefore, in this work the equilibrium molecular dynamics method (Green-Kubo method) is used to study the effect of point defects on the heat transfer properties of cubic SiC (<i>β</i>-SiC or 3<i>C</i>-SiC) with the help of the Tersoff-type potential. The point defects considered include Si interstitial atoms (Si<sub>I</sub>), Si vacancies (Si<sub>V</sub>), Si anti-site atoms (Si<sub>C</sub>), C interstitial atoms (C<sub>I</sub>), C vacancies (C<sub>V</sub>) and C anti-site atoms (C<sub>Si</sub>). It is found that the thermal conductivity (<i>λ</i>) decreases with the increase of the point defect concentration (<i>c</i>). The excessive thermal resistance (Δ<i>R</i> = <i>R</i><sub>defect </sub>– <i>R</i><sub>perfect</sub>, <i>R</i> = 1/<i>λ</i>, <i>R</i><sub>defect</sub> is the thermal resistance of the defective material, and <i>R</i><sub>perfect</sub> is the thermal resistivity of the material without defects) has a linear relation with the concentration of point defects in the considered range (0.2%–1.6%), and its slope is the thermal resistivity coefficient. It can be found that the thermal resistivity coefficient of vacancy and interstitial atoms are higher than that of anti-site atoms; the thermal resistivity coefficient of point defects at high temperature is higher than at low temperature; the thermal resistivity coefficient of Si vacancies and Si interstitial atoms are higher than that of C vacancies and C interstitial atoms. These results are helpful in predicting the thermal conductivity of silicon carbide under irradiation and controlling the thermal conductivity of silicon carbide.

Channel size-dependent TED effect in MOSFETs with infrared rapid thermal anneal

Boron transient enhanced diffusion (TED) causes reverse short channel effect, and threshold voltage (Vt) increases abnormally, which seriously affects the device performance and yield. The Vt increment is different with different channel size. To investigate channel impurity distribution and the influence of channel size on TED, Vt adjustment ion-implantation, LDD ion-implantation and carbon co-implantation experiments were performed on 40 nm CMOS process, measuring Vt with different channel size and process, and using TCAD tools for process simulation. Experiments results show that Vt rises first with channel length decreasing and then drops sharply after reaching the maximum at 0.55 μm. The Vt -L curve slope decreases when channel width decreases. Vt decreases with channel width and it is decreasing faster and faster when channel length is constant. The interstitial Si atoms are injected by LDD ion-implantation and diffuse into channel, while boron pile up at the LDD-channel boundary. However, boron leak into the shallow trench isolation (STI) area at the corner formed by LDD and channel. Both pile-up and leakage control boron concentration distribution in channel. The Vt shift induced by boron TED is channel size-dependent, and high energy carbon co-implantation and infrared rapid thermal anneal can suppress TED effect effectively.

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.

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.

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.

Control of grown-in defects and oxygen precipitates in silicon wafers with DZ-IG structure by ultrahigh-temperature rapid thermal oxidation

A new control technique for achieving compatibility between crystal quality and gettering ability for heavy metal impurities was demonstrated for a nitrogen-doped Czochralski silicon wafer with a diameter of 300 mm via ultra-high temperature rapid thermal oxidation (UHT-RTO) processing. We have found that the DZ-IG structure with surface denuded zone and the wafer bulk with dense oxygen precipitates were formed by the control of vacancies in UHT-RTO process at temperature exceeding 1300 °C. It was also confirmed that most of the void defects were annihilated from the sub-surface of the wafer due to the interstitial Si atoms that were generated at the SiO2/Si interface. These results indicated that vacancies corresponded to dominant species, despite numerous interstitial silicon injections. We have explained these prominent features by the degree of super-saturation for the interstitial silicon due to oxidation and the precise thermal properties of the vacancy and interstitial silicon.

Identification of donor deactivation centers in heavily As-doped Si using time-of-flight medium-energy ion scattering spectroscopy

Electrically-inactive arsenic (As) complexes in silicon are investigated using time-of-flight medium-energy ion scattering spectroscopy. In heavily As-doped Si, the As atoms that are segregated in the Si interface region just below the SiO2 are found to be in interstitial forms (Asi), while the As atoms in the bulk Si region are found to be in the substitutional form (AsSi). Despite the substitutional form of As, most of the As are found to be electrically inactive in the bulk region, and we identify the As to be in the form of a 〈111〉-oriented AsSi-Si-vacancy (AsSi-VSi) complex. The Asi atoms in the interface Si region are found to exist together with Si-interstitial atoms (Sii), suggesting that the Asi atoms in the interface Si region accompany the Sii atoms.

PECULIARITIES OF A DEFECT GENERATION DURING A HEAT TREATMENT OF LARGE DIAMETER DISLOCATION−FREE SILICON WAFERS WITH SPECIFIED DISTRIBUTION OF OXYGEN−CONTAINING GETTERING CENTRES

For this purpose the opportunities of perfect layer formation during RTA have been analyzed in dislocation−free silicon wafers. The RTA application is based on an opportunity of effective influence on a distribution of oxygen precipitate density on wafer thickness by means of control of vacancies and interstitial atoms distributions. However the decision of this important task is connected with an oc-currence of large local wafer stresses concentrated near fastening supports and a significant bend of large diameter Si wafers. Therefore in this project the mathematical modeling of three−dimension strain state and defect formation in large diameter Si wafer were investigated: the various ways of wafer fastening were analyzed and the opportunities of stresses reduction in Si wafers were determined. For the description of RTA defect formation the mathematical model taking into account of diffusion−recombination processes of vacancies and interstitial Si atoms, and also formation of vacancy clusters have been applied. On the basis of this model the time thermal RTA parameters were determinated: heating mode, hold time at the maximal temperature and cooling rate of wafer. They provide a formation of required perfect layer near wafer surface contained the corresponding vacancy concentration and cluster density on wafer thickness. The calculated results have been verified by authors of this project on test samples investigated by Light Microscopy (LM) and Transmission Electron Microscopy (TEM). Detailed LM and TEM researches of microdefect distributions and morphology have been carried out for the experimental Si wafers subjected to various RTA modes and multistage heat treatment in Belarusian plant «Integral».

Impact of Rapid Thermal Oxidation at Ultrahigh-Temperatures on Oxygen Precipitation Behavior in Czochralski-Silicon Crystals II

Oxygen precipitates (OPs) in a Czochralski silicon (Cz-Si) wafer can degrade the performance of semiconductor devices if they are in the active region of the Si wafer, i.e., the surface layer. On the other hand, they can improve device fabrication yield through their ability to enhance impurity gettering and through mechanical strengthening, both of which are important characteristics for semiconductor device fabrication. 1,2 Thus, the OPs must be controlled in an appropriate manner depending on the structure of the intended semiconductor devices and the production process employed. More precise and uniform control of OPs in Si wafers will be a significant factor for future advanced semiconductor devices. To understand this very important issue, we previously investigated the re-formation effect of OP nuclei using ultrahigh-temperature rapid thermal oxidation (RTO), at over 1300 ◦ C, and achieved wide and precise controllability of new OP nuclei. 3 This technique also demonstrated a remarkable ability to eliminate heterogeneity effects such as OP nuclei or related defects in the grown crystal. Ultrahigh-temperature annealing using rapid thermal processing (RTP) has significant advantages in terms of excellent temperature uniformity in the radial direction of the Si wafer as compared to the Cz-Si crystal growth process. As mentioned above, ultrahigh-temperature RTO showed a remarkable ability to control the effects of the OP nuclei. The behavior of OP nuclei in Cz-Si crystals is strongly related to point defects such as vacancies and Si interstitials. 4 Vacancies promote the formation of OP nuclei because these nuclei are formed as a complex between oxygen atoms and vacancies. It is generally known that annealing in an oxygen atmosphere is not a practical way to increase vacancy concentration because Si interstitials are dominant in the Si wafer due to the injection of Si interstitials from the oxidized surface. However, as we previously reported, 3 the behavior of OP nuclei can be controlled by changing the dominant point defects from Si interstitials to vacancies depending on the difference of each thermal equilibrium concentration at ultrahigh temperatures, even though the oxidation atmosphere is used for RTP. Furthermore, in the case of ultrahigh-temperature RTO, it is expected that Si interstitials also exist at high concentration due to the Si surface oxidation even though the dominant point defects are vacancies. Interstitial Si point defects are expected to annihilate vacancy-related defects such as void defects when enough interstitial Si atoms exist. 5 The void defects also influence the semiconductor device performance; therefore, in addition to OP control, annihilating void defects is a very important goal. It is well known that RTP in a nitrogen or argon atmosphere does not effectively annihilate void defects under the surface of the Si wafer. 6‐8 Ultrahigh-temperature RTO would gain a further advantage over RTP in a nitrogen or argon atmosphere if annihilation of void defects is confirmed. In this study, the annihilation behaviors of void defects in the case of the ultrahigh-temperature RTO were evaluated in detail.

Si isotopic structure of the infrared absorption of the fully hydrogenated vacancy in silicon

An infrared absorption spectrum consisting in three lines observed around 2223 cm(-1) at liquid helium temperature characterizes a defect common in silicon crystals containing hydrogen. Several investigations of this spectrum have converged towards its assignment to a fully hydrogenated lattice vacancy defect V(Si-H)4. However, the fact that the ratios of the intensities of the three lines have been reported to be proportional to the natural abundances of the three silicon isotopes suggests that only one Si atom is involved in the defect, apparently contradicting the above assignment. In this paper, the spectroscopic investigation of this defect is revisited and the Si-related isotopic structures of V(Si-H)4 and V(Si-D)4 defects are modeled. It is shown that the near proportionalities observed between the intensities of these lines and the abundances of the Si isotopes are fortuitous. Our analysis of the isotope dependence of the 2223 cm(-1) line finds the V(Si-H)4 model to be correct and that the model of a single interstitial Si atom complexed with H can be rejected. The investigation is extended to the analysis of tetra-hydrogenated vacancy trapped by a carbon atom.

Evolution of atoms with special coordination number in β-SiC with temperature

The characteristics and mechanisms of evolution of Si and C atoms with different coordination number were studied using molecular dynamics and molecular static. Relaxation energy of these systems and the displacement of these special atoms from their original positions have been investigated. The results showed that some of these special Si atoms moved away from their lattice sites and may become Si interstitial atoms at 300K. As temperature increased, more intrinsic defects were detected. In the case of the one-coordinated C atom, this atom did not move away from its lattice site until 600K, turning into a C interstitial atom. Then it became a CSi antisite after 1200K. In general, the relaxation energies and the displacement decrease with increasing coordination number. The differences between special Si and the equivalent special C systems strongly depend on the temperature.

Influence of radiation defects on diffusion of arsenic and antimony in implanted silicon

Diffusion of implanted Sb and As in silicon layers with various contents of radiation defects is investigated during furnace thermal annealing and rapid thermal annealing (RTA). The defect concentration was varied by the additional introduction of Si+ ions. As the defect concentration in the layer increases, the antimony diffusivity increases both during lamp annealing and during furnace thermal annealing, which is governed by diffusion over excess vacancies. The As diffusivity increases with an increase in the concentration of radiation defects in the layer during the lamp annealing and decreases during furnace thermal annealing. The increase in the As diffusivity during RTA is attributed to interstitial Si atoms. The observed decrease in the As diffusivity is caused by the impurity capture by excess vacancies as the traps. However, at defect concentrations much higher than the impurity concentration, the As diffusivity increases but remains substantially lower than the intrinsic value. It follows from the results that the rate of intrinsic As diffusion along the interstitial channel is higher than along the vacancy channel.

Nanoscale engineering of radiation tolerant silicon carbide

Radiation tolerance is determined by how effectively the microstructure can remove point defects produced by irradiation. Engineered nanocrystalline SiC with a high-density of stacking faults (SFs) has significantly enhanced recombination of interstitials and vacancies, leading to self-healing of irradiation-induced defects. While single crystal SiC readily undergoes an irradiation-induced crystalline to amorphous transformation at room temperature, the nano-engineered SiC with a high-density of SFs exhibits more than an order of magnitude increase in radiation resistance. Molecular dynamics simulations of collision cascades show that the nano-layered SFs lead to enhanced mobility of interstitial Si atoms. The remarkable radiation resistance in the nano-engineered SiC is attributed to the high-density of SFs within nano-sized grain structures that significantly enhance point defect annihilation.