Dislocations In Si Research Articles

Enabling plastic co-deformation of disparate phases in a laser rapid solidified Sr-modified Al–Si eutectic through partial-dislocation-mediated-plasticity in Si

Nano-scale eutectics, such as rapid solidified Al–Si, exhibit enhanced yield strength and strain hardening but plasticity is limited by cracking of the hard phase (Si). Mechanisms that may suppress cracking and enable plastic co-deformation of soft and hard phases are key to maximizing plasticity in these high-strength microstructures. Using a combination of laser rapid solidification and chemical (Sr) modification, we have synthesized fully eutectic Al–Si microstructures with heavily twinned Si nano-fibers that exhibit high hardness up to 2.9 GPa, and high compressive flow strength (∼840 MPa) with stable plastic flow to ∼26% plastic strain. After deformation, the hard Si(Sr) fibers did not exhibit cracks, but a high density of stacking faults were observed in the Si(Sr) fibers suggesting partial dislocation mediated plasticity. Mechanisms for suppression of cracking and activation of partial dislocations in Si deformed at room temperature are discussed in terms of nanoscale fiber geometry with reduced aspect ratio and lowering of the Peierls barrier in chemically-modified, nano-twinned Si fibers.

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.

Transport of Charge Carriers along Dislocations in Si and Ge

Experimental observations and quantum mechanical device simulations point to different electronic properties of dislocations in silicon and germanium. The experimental data suggest a supermetallic behavior of the dislocations in Si and thus the high strain in the dislocation core is thought to cause the confinement of the charge carriers, which leads to the formation of a 1D electron gas along a dislocation (quantum wire). The resulting significant increase in the electron concentration corresponds to a marked increase in the drain current of metal–oxide–semiconductor field‐effect transistor (MOSFET). The specific resistance of an individual dislocation in Ge is about nine orders of magnitude higher than for a dislocation in Si. The experimental measurements of the strain in dislocation cores in Ge are still missing. Based on the band structure data, the generation of a strain equivalent to that of the dislocation cores in Si appears to be very challenging because of the transition from an indirect into a direct semiconductor with about tenfold lower strain levels. The lower strain in the dislocation core in germanium may not support the carrier confinement as proposed for the dislocation core of silicon, and consequently 1D electron gases are not expected to form along the dislocations in Ge.

Correction to: Generation and Auto-Revealing of Dislocations in Si During Macropore Etching

On page 5116, last paragraph in the XRD Data section, there is an error. The corrected sentence is as follows:

Study of sputtered Cu2ZnSnS4 thin films on Si

Integrating commercialized Si solar cells with eco-friendly and earth-abundant Cu2ZnSnS4 (CZTS) film is a promising method to increase power conversion efficiency and hence reduce the levelized cost of electricity. However, synthesis of CZTS thin film on Si as well as the study of the interaction between the two materials, which are crucial for good performance of CZTS/Si two-terminal devices, are areas that have been less investigated. Here, we grow polycrystalline CZTS thin films on Si (1 0 0) substrate by sputtering and study the properties of the CZTS thin film and interface between the CZTS and Si. The CZTS shows uniform microstructure and optimal optical properties. A CZTS solar cell which is fabricated on Si shows a photovoltaic response although subjected to high serious resistance, and Cu diffusion was found from CZTS into Si, which caused needle-like dislocations in Si. Therefore, an effective conductive barrier layer between CZTS and Si is desirable to inhibit Cu from diffusing into Si for tandem solar cell purposes. The study offers valuable input for understanding the properties of CZTS thin film sputtered from single target sputtering and the impact on the interfaces and underlying Si, suggesting concerns that manufacturers need to be aware of for its application in tandem solar cells based on Si.

Generation and Auto-Revealing of Dislocations in Si During Macropore Etching

The influence of the variations in the photoelectrochemical etching regimes of macropores in n-Si (within the limits of V. Lehmann optimums) on the quality of structures was studied. At some regimes, generation of screw (cylindrical or spiral) dislocations during the etching process under normal conditions was observed. First, dislocations are formed, and then macropores are etched, mainly on near-surface traces of dislocations. We call this process “auto-revealing”. The values of residual lattice distortions due to deformation of the silicon plate during the etching process were determined by x-ray diffraction on a structure obtained in the acceptable boundary regime.

Effect of a Low-Temperature Si Underlayer on the Photoluminescence of Misfit Dislocations in Si(001)Si1 − xGe x Heterostructures with Ge-Rich Alloy Layers

The effect a low-temperature Si underlayer has on the photoluminescence of misfit dislocations in Si(001)Si1 – xGe x heterostructures with high Ge contents in a SiGe alloy layer is investigated. It is found that the introduction of this layer prevents the formation of dislocations in the alloy layer.

Concerning vacancy defects generated by moving dislocations in Si

In this paper we present experimental results of investigations of vacancy complexes Vxtrail (“trail defects”), generated by moving dislocations in silicon. For detection of Vxtrail defects we used their reactions with atoms of transition metals. LBIC and DLTS methods were used for investigations of electrically active defects. We show that the probability of generation of Vxtrail defects by a moving dislocation decreases with increasing temperature of plastic deformation with activation energy of about 2.3 eV.

Maximum usable thickness revisited: Imaging dislocations in Si by modern high-voltage scanning transmission electron microscopy

We have quantitatively evaluated the usable thickness of specimens in scanning transmission electron microscopy (STEM) at 1 MV using a wedge-shaped Si(110) single crystal including artificially introduced high-density dislocations. The width of dislocation images was employed as a criterion for the quantitative evaluation of usable thickness. Superior usable thickness in STEM than in TEM was found; the obtained results were 14.7 µm for STEM and 5.8 µm for TEM. In particular, in STEM, dislocations can be observed as thin lines with 10–15 nm width in the thickness range up to 10 µm. The latest high-voltage STEM is useful for imaging crystal defects in thick semiconductors.

Ab initio phonon scattering by dislocations

Heat management in thermoelectric and power devices as well as in random access memories poses a grand challenge and can make the difference between a working and an abandoned device design. Despite the prevalence of dislocations in all these technologies, the modeling of their thermal resistance is based on 50-year-old analytical approximations, whose simplicity was driven by practical limitations rather than physical insight. We introduce an efficient ab initio approach based on Green's functions computed by two-dimensional reciprocal space integration. By combining elasticity theory and density functional theory, we calculate the scattering strength of a ${90}^{\ensuremath{\circ}}$ misfit edge dislocation in Si. Because of the breakdown of the Born approximation, earlier literature models fail, even qualitatively. We find that a dislocation density larger than ${10}^{9}\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$ is necessary to substantially influence thermal conductivity at room temperature and above. We quantify how much of the reduction of thermal conductivity measured in nanograined samples can be explained by realistic dislocation concentrations.

Reaction pathway analysis for shuffle-set 60° perfect dislocation in Si

In this work, the EDIP potential is employed for representing silicon and the shuffle-set 60° perfect dislocation motion is investigated by reaction pathway analysis. There are three possible shuffle-set 60° perfect dislocation core structures named as S1, S2 and S3. The activation energy barriers of the kink migration and nucleation in S1and S2 types are calculated by CI-NEB method. The simulation results show that the critical resolved shear strain of the shuffle-set dislocation in S1 type is around 5%, and the S1 type is the dominate one in the shear strain region of 0 to 5%. During the shear strain from 5to 11.81%, the dislocation moves as the S1 core kink nucleation and migration, meanwhile the S1 dislocation core is in process of transforming into S2. More interestingly, both S1 and S2 dislocation core structures is observed along the dislocation line in this shear strain regime, which could response to the missing observation of long segment dislocation line in the experiment.

Electronic and Optical Properties of Dislocations in Silicon

Dislocations exhibit a number of exceptional electronic properties resulting in a significant increase of the drain current of metal-oxide-semiconductor field-effect transistors (MOSFETs) if defined numbers of these defects are placed in the channel. Measurements on individual dislocations in Si refer to a supermetallic conductivity. A model of the electronic structure of dislocations is proposed based on experimental measurements and tight binding simulations. It is shown that the high strain level on the dislocation core—exceeding 10% or more—causes locally dramatic changes of the band structure and results in the formation of a quantum well along the dislocation line. This explains experimental findings (two-dimensional electron gas and single-electron transitions). The energy quantization within the quantum well is most important for supermetallic conductivity.

Temperature dependence of the stacking fault energy of glide set-dissociated dislocations in Si

Recently, it was found that the dissociation distance of glide set dislocations introduced in Si just below the melting temperature by laser shock peening (LSP) is unusually wide (Iwata et al. J. Jpn Inst. Met. Materi.,79(2015),308–314). In order to distinguish whether or not this is to be attributed to uncorrelated motions of leading and trailing Shockley partials or the intrinsic temperature dependence of the stacking fault energy (SFE), dislocations introduced by LSP were annealed at 1350 °C, which should be high enough for the uncorrelated partials to assume the equilibrium correlated configuration. It was found that this unusual widening of a dissociated dislocation introduced by LSP is attributed to uncorrelated motions of Shockley partials. Following this conclusion, the temperature dependence of the intrinsic SFE of Si was determined on correlated dissociated dislocations up to near the melting temperature. The intrinsic SFE of Si shows only negligibly small temperature dependence from 400 °C up to near the melting temperature.

Electronic properties of dislocations

Dislocations exhibit a number of exceptional electronic properties resulting in a significant increase in the drain current of MOSFETs if defined numbers of these defects are placed in the channel. Measurements on individual dislocations in Si refer to a supermetallic conductivity. A model of the electronic structure of dislocations is proposed based on experimental measurements and tight-binding simulations. It is shown that the high strain level on the dislocation core—exceeding 10 % or more—causes locally dramatic changes in the band structure and results in the formation of a quantum well along the dislocation line. This explains experimental findings (two-dimensional electron gas, single-electron transitions). The energy quantization within the quantum well is most important for supermetallic conductivity.

Interstitial iron impurities at cores of dissociated dislocations in silicon

Dislocations play an important role in semiconductor devices made of crystalline silicon (Si). They are known to be strongly performance-limiting defects in solar cell applications, since they act as preferred segregation sites for metallic impurities. In this work we investigate the segregation of iron (Fe) to the cores of the ${30}^{\ensuremath{\circ}}$ and ${90}^{\ensuremath{\circ}}$ partial dislocations in Si using atomistic calculations based on first-principles density functional theory. Our simulations show that interstitial Fe impurities segregate readily to all investigated cores and the driving force for the segregation increases with impurity concentration. Moreover, our analysis of the electronic structure reveals the existence of deep defect levels within the band gap that can be related to experimental observations by deep-level transient spectroscopy.

Interplay of Ni and Au Atoms with Dislocations and Vacancy Defects Generated by Moving Dislocations in Si

We show experimentally that dislocations in Si crystals can generate some unknown vacancy complexes Vxtrail in their slip planes during their motion at 600°C. Most of these “dislocation trail defects” are not electrically active but can be detected by their reaction with gold atoms during in-diffusion experiments. It was also shown that contrary to gold, the Vxtrail-complexes do not react with interstitial Ni atoms. It means that the binding energy Ebind of Vxtrail complexes is quite high (Ebind>2.5eV), higher than the binding energy of vacancy complexes generated during FZ-Si crystal growth. It was also shown that Ni in-diffusion results in a strong increase of electron-hole recombination at dislocations and in a strong increase of dislocation-related DLTS C-line.

Multistrata Subsurface Laser-Modified Microstructure With Backgrind-Assisted Controlled Fracture for Defect-Free Ultrathin Die Fabrication

We report the development of multistrata subsurface IR ( $1.342~\mu \text{m}$ ) nanosecond pulsed laser die singulation [stealth dicing (SD)] on high backside reflectance (up to 82%) Si wafers. We study the microstructural properties and formation mechanisms of the subsurface Si dislocation belt layer with respect to laser scanning speed, pulse laser energies, and interstrata distances. We optimize and exploit the multistrata interactions between generated thermal shock waves and the preceding dislocation belt layers formed to initiate frontal crack fractures that separate out the individual dies from within the interior of the wafer. A new partial-SD before grinding (p-SDBG) integration scheme based upon the tandem use of three-strata SD for controlled crack fracture toward the frontside of the wafer followed by static loading from backgrinding to complete full kerf separation is demonstrated. The optimized three-strata SD process and p-SDBG integration scheme can be used to compensate for the high backside reflectance wafers to produce defect-free eight die stacks of 25- $\mu \text{m}$ -thick mechanically functional and 46- $\mu \text{m}$ -thick electrically functional 2-D NAND memory dies.

Control of SiO2/Si interface defects generation during thin dielectric film etching using CHxFy/Ar/O2 plasma

We investigated the quantitative control of SiO2/Si interface defects caused by CHxFy/Ar/O2 plasma etching. Both the number and the cause of interface defects generation strongly depended on the residual thicknesses of SiO2. When the residual thickness becomes small, in addition to the VUV/UV irradiation, ion injection caused a remarkable increase in the number of interface defects associated with Si dislocation. Complete recovery from damage was difficult by low-temperature thermal annealing, especially ion-induced damage. Ion-induced damage was suppressed by controlling the residual thickness of SiO2 to be larger than the ion penetration depth. VUV/UV-induces damage could be effectively suppressed by using a light shield layer such as SiN. Moreover, VUV/UV-induces damage under a fine space pattern is expected to be suppressed in comparison with a wide-open pattern. Thus, the process design of a film stack, pattern, etching condition, and thermal annealing condition are important for controlling SiO2/Si interface defect generation during plasma processing.

The Properties of Shuffle Screw Dislocations in Semiconductors Silicon and Germanium

The dislocation widths, Peierls barriers and Peierls stresses for shuffle screw dislocations in diamond structure crystals, Si and Ge, have been calculated by the improved P-N theory. The widths are about 0.6b, where b is the Burgers vector. The Peierls barrier for shuffle screw dislocation in Si and Ge, is about 3.61~4.61meV/Å and 5.31~13.32meV/Å, respectively. The Peierls stress is about 0.28~0.33GPa and 0.31~0.53GPa, respectively. The calculated Peierls barriers and stresses are likely the results of shuffle screw dislocation with metastable core which is centered on the bond between two atoms.

Multi-scale simulation of the stability and diffusion of lithium in the presence of a 90° partial dislocation in silicon

The stable positions, binding energies, and dynamic properties of Li impurity in the presence of a 90° partial dislocation in Si have been studied by using the multi-scale simulation method. The corresponding results are compared with the defect-free Si crystal in order to reflect how the dislocation defect affects the performances of Li-ion batteries (LIBs) at the atomic level. It is found that the inserted Li atom in the dislocation core and nearest regions is more stable, since the binding energies are 0.13 eV to 0.52 eV larger than the bulk Si. Moreover, it is easier for Li atom to diffuse into those defect areas and harder to diffuse out. Thus, Li dopant may tend to congregate in the dislocation core and nearest regions. On the other side, the 90° partial dislocation can glide in the {111} plane accompanied by the diffusion of Li impurity along the pentagon ring of core. In addition, the spacious heptagon ring of dislocation core can lower the migration barrier of Li atom from 0.63 eV to 0.34 eV, which will enhance the motion of the dopant. Therefore, the presence of 90° partial dislocations may provide a fast and favorable diffusion path for the congregated Li impurity, which finally facilitates the lithiation of LIBs.