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Owing to the advanced fabrication technology of silicon, silicon waveguides are particularly attractive for implementing all-optical signal processing devices and switches. Therefore, in this paper, a silicon-on-silica waveguide that consists of four slots arranged in the shape of letter E is proposed to be employed as the building block for simulating fundamental all-optical logic gates (AOLGs), including XOR, AND, OR, NOT, NOR, NAND, and XNOR, at 1.55 μm telecommunications wavelength. The operation concept of these logic gates relies on the constructive and destructive interference that results from the phase difference induced by optical beams that are incident on the E-shaped waveguide. The performance of the target logic gates is assessed against the contrast ratio (CR) metric. Moreover, the dependence of the spectral transmission on the device's key operating parameters is investigated and assessed. Compared to other reported designs, the results obtained by conducting simulations using the finite-difference-time-domain in lumerical commercial software show that the proposed waveguide can operate at a higher speed of 80 Gb/s and attain higher CRs of 36, 39, 35.5, 28.8, 30, 38, and 36.7 dB for logic XOR, AND, OR, NOT, NOR, NAND, and XNOR, respectively. This suggests that by using the proposed scheme, AOLGs could be realized more feasibly with greater performance and faster operation toward satisfying the present and future needs of light wave circuits and systems. [ABSTRACT FROM AUTHOR]

Structure-engineered silicon exhibits a wealth of unique optical properties below its bandgap, which holds promise for mid-infrared and terahertz applications such as photodetection, thermophotovoltaics, radiative cooling, and spectroscopy. In this paper, we investigate enhancement mechanisms of sub-bandgap absorption of black silicon fabricated into periodic pyramids. Our measurements indicate that the pyramid structure leads to an enhanced broadband absorption in the wavelength region from 1.5 to 13.07 μm with an efficiency of over 80%. The broadband absorption enhancement is shown to originate from the Rayleigh–Wood anomaly, localized magnetic plasmonic resonance, and graded-index effect, which together facilitate the interaction between light and free-carriers in silicon. These results are helpful for understanding the interaction between light and black silicon. [ABSTRACT FROM AUTHOR]

Precise control of dopant placement is crucial for the reproducible, and reliable, nanoscale semiconductor device fabrication. In this paper, we demonstrate an atomic force microscopy (AFM) probe assisted localized doping of aluminum into an n-type silicon (100) wafer to generate nanoscale counter-doped junctions within two nanometers of the silicon-air interface. The local doping results in changes in electrostatic potential, which are reported as contact potential difference, with nanoscale spatial resolution. In contrast to the literature where nano-mechanical defects in, or contaminants on, silicon substrates can result in measurable changes in the chemical potential of the near-surface, additional thermal treatment was needed to electrically activate the aluminum dopants in our current work. Unfortunately, the thermal activation step also caused the dopants to diffuse and geometric distortions in the doped area, i.e., broadening and blurring of the electrically distinct areas. The results from optimization efforts show that the "active" dopant concentration depended primarily on the thermal anneal temperature; additional AFM-tip dwell time during the aluminum implantation step had no meaningful impact on the electrical activity of the doped sites. [ABSTRACT FROM AUTHOR]

AlN-on-Si can be considered as a model system for heteroepitaxial growth of highly mismatched materials. Indeed, AlN and Si drastically differ in terms of chemistry, crystalline structure, and lattice parameters. In this paper, we present a transmission electron microscopy and grazing incidence X-ray diffraction study of the microstructure of AlN layers epitaxially grown on Si (111) by molecular beam epitaxy. The large interfacial energy due to the dissimilarities between AlN and Si results in a 3D Volmer-Weber growth mode with the nucleation of independent and relaxed AlN islands. Despite a well-defined epitaxial relationship, these islands exhibit in-plane misorientations up to 6°–7°. We propose a model which quantitatively explains these misorientations by taking into account the relaxation of the islands through the introduction of 60° a-type misfit dislocations. Threading dislocations (TDs) are formed to compensate these misorientations when islands coalesce. TD density depends on two parameters: the islands' misorientation and density. We show that the former is related to the mismatch between AlN and Si, while the latter depends on the growth parameters. A large decrease in TD density occurs during the 3D growth stage by overlap and overgrowth of highly misoriented islands. On the other hand, the TD density does not change significantly when the growth becomes 2D. The proposed model, explaining the misorientations of 3D-grown islands, may be extended to other (0001)-oriented III-nitrides and more generally to any heteroepitaxial system exhibiting a 3D Volmer-Weber growth mode with islands relaxed thanks to the introduction of mixed-type misfit dislocations. [ABSTRACT FROM AUTHOR]

In the analysis of highly doped silicon, energy band gap narrowing (BGN) and degeneracy effects may be accounted for separately, as a net BGN in conjunction with Fermi-Dirac statistics, or lumped together in an apparent BGN used with Boltzmann statistics. This paper presents an experimental study of silicon highly doped with boron, with the aim of evaluating the applicability of previously reported BGN models. Different boron diffusions covering a broad range of dopant densities were prepared, and their characteristic recombination current parameters J0 were measured using a contactless photoconductance technique. The BGN was subsequently extracted by matching theoretical simulations of carrier transport and recombination in each of the boron diffused regions and the measured J0 values. An evaluation of two different minority carrier mobility models indicates that their impact on the extraction of the BGN is relatively small. After considering possible uncertainties, it can be concluded that the BGN is slightly larger in p+ silicon than in n+ silicon, in qualitative agreement with theoretical predictions by Schenk. Nevertheless, in quantitative terms that theoretical model is found to slightly underestimate the BGN in p+ silicon. With the two different parameterizations derived in this paper for the BGN in p+ silicon, both statistical approaches, Boltzmann and Fermi-Dirac, provide a good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

This paper reconsiders the mathematical formulation for the conventional nonparabolic band model and discusses how the nonparabolicity of the conduction band impacts the effective masses of electrons that are confined within the barriers. Since the conventional simplified model for band nonparabolicity does not include the external potential effect as a perturbation, it is examined whether this perturbation can be implemented into the conventional model for usefulness. When the perturbation energy is smaller than the unperturbed energy, the insertion of the perturbation energy term into the conventional expression for the nonparabolic band model is reasonably valid. It is demonstrated that this approximation is actually accurate given a sub-10-nm-thick Si layer surrounded by an SiO2 layer. A major part of this discussion is focused on the low-dimensionality electron system confined with insulator barriers so this study contributes to the analysis of future electron devices. To support this consideration, this paper proposes an analytical expression for the conduction-band effective mass of electrons including the term of band nonparabolicity. [ABSTRACT FROM AUTHOR]

Correct identification of local configurations of dopants and point defects in random alloys poses a challenge to both computational modeling and experimental characterization methods. In this paper, we propose and implement a computationally efficient approach to address this problem. Combining special quasirandom structures, virtual crystal approximation, and real-space lattice static Green's functions, we are able to calculate, at moderate computational cost, the local phonon density of states (LPDOSs) of impurities in a random alloy crystal for system sizes, surpassing the capabilities of a conventional, cubic-scaling, density functional theory. We validate this method by showing that our LPDOS predictions of substitutional silicon in GaAs and InAs are in excellent agreement with the experimental data. For the case study, we investigate a variety of local configurations of Si and Se substitutional dopants and cation vacancies in quasirandom In 0.5 Ga 0.5 As alloys. In all cases, the impurity LPDOS in a random alloy exhibits qualitatively different signatures from those in the pure binary compounds GaAs and InAs. Specifically, they are characterized by a wide continuous band (rather than narrow discrete peaks) of vibrational modes at frequencies typically higher than the bulk modes, a sign of coupling between localized vibrations of the impurity and those of its random neighboring host atoms. The accuracy and computational cost of this approach open a way to the simulation of impurities in random structures on a large scale and the prediction of vibrational signatures of alloys with defects. [ABSTRACT FROM AUTHOR]

A response to a commentary on the paper "A Model for Internal Photoemission at High-k Oxide/Silicon Energy Barriers" published within the issue is presented. He describes the results presented by the study authors on photoelectric emission from silicon surfaces. He also examines the assertion that the modified Powell equation used would lead to a different fraction of electrons which may potentially surmount the interface barrier.

This paper reports the magnetic properties of 2 μm thick electroplated isotropic L10 CoPt films on silicon at temperatures ranging from 300 K to 790 K, as well as the room-temperature properties of the films after various thermal cycles. Electroplated equiatomic CoPt layers require a post-deposition annealing typically at ∼973 K to induce L10 ordering so that they exhibit hard magnetic properties at room temperature. However, the influence of temperature on these post-deposition annealed films is an important consideration for their utility in end applications. Here, a reversible temperature coefficient of remanence of -0.11% K-1 is measured along with a maximum operating temperature of 400 K (recovery to 95% of the initial remanence). The maximal energy density of the films is reduced by 50% at a temperature of 550 K. However, the original room-temperature magnetic properties are shown to be fully recoverable by remagnetization after various thermal cycles-800 K for 15 min in Ar, 373 K for 168 h in air, and 358 K for 168 h in air at 85% relative humidity. These investigations indicate that the electroplated L10 CoPt layers, like bulk, exhibit good thermal robustness, satisfying a key requirement for their use in end applications, such as magnetic microsystems. [ABSTRACT FROM AUTHOR]

This paper provides a detailed description explaining how to calculate the relation between the silicon Raman frequency and local stress or strain in the silicon, applied to stress measurements in microelectronics. This relation is well known for measurements from the (100) surface of silicon. However, it is often used in the wrong way, neglecting non-zero stress tensor elements. Especially, in current 3D microelectronics technology, where the stress caused by through Si vias or microbumps is of large importance, the vertical stress component, which highly affects the measured Raman frequency shift, is often erroneously neglected. In addition, the equations for the (100) surface are also often used incorrectly for cross-sectional measurements from a (110) surface. In this paper, different ways to calculate the relation between Raman frequency and triaxial stress, and the related Raman peak intensities, are discussed in detail. [ABSTRACT FROM AUTHOR]

Silicon solar cells containing boron and oxygen are one of the most rapidly growing forms of electricity generation. However, they suffer from significant degradation during the initial stages of use. This problem has been studied for 40 years resulting in over 250 research publications. Despite this, there is no consensus regarding the microscopic nature of the defect reactions responsible. In this paper, we present compelling evidence of the mechanism of degradation. We observe, using deep level transient spectroscopy and photoluminescence, under the action of light or injected carriers, the conversion of a deep boron-di-oxygen-related donor state into a shallow acceptor which correlates with the change in the lifetime of minority carriers in the silicon. Using ab initio modeling, we propose structures of the BsO2 defect which match the experimental findings. We put forward the hypothesis that the dominant recombination process associated with the degradation is trap-assisted Auger recombination. This assignment is supported by the observation of above bandgap luminescence due to hot carriers resulting from the Auger process. [ABSTRACT FROM AUTHOR]

III-V optoelectronics grown epitaxially on Si substrates have large networks of dislocations due to a lattice constant mismatch between the device layers and the substrate. Recombination-enhanced dislocation glide (REDG) allows these dislocations to move and increase in length during device operation, which degrades performance. In this paper, we study REDG dynamics of threading dislocations in situ in (In)AlGaAs double heterostructures grown on Si substrates using scanning electron microscopy cathodoluminescence. The driving force for REDG arises due to the coefficient of thermal expansion differences between Si and the III-V layers leading to large residual strains in the films. Tracking of threading dislocations as moving dark spot defects reveals glide characteristics that vary based on the nature of the dislocation. Remarkably, the alloying of a few atom percent of indium using metamorphic structures arrests threading dislocation glide by more than two orders of magnitude. Finally, we present REDG-based filtering as a pathway to reducing the threading dislocation density in select areas, removing a large fraction of the mobile dislocations. Together, these techniques will enable the understanding of dislocation–dislocation and carrier–dislocation interactions that have so far remained elusive during device operation, leading to reliable III-V integrated optoelectronics on silicon. [ABSTRACT FROM AUTHOR]

For the ⟨ 1 1 ¯ 0 ⟩ screw dislocation (nondissociated) in silicon, there are three types of core structures that are, respectively, referred to as the shuffle-set dislocation (A-core), glide-set dislocation (C-core), and mix-set dislocation (B-core). Each type of core further displays a planar or nonplanar (fourfold) configuration. In this paper, in the context of the generalized Peierls theory, the energy functional and equation of equilibrium of a screw dislocation with a nonorthogonal fourfold structure is derived and is used to investigate the structure and energy of the ⟨ 1 1 ¯ 0 ⟩ screw dislocation in silicon. We find that the energy of the shuffle-set dislocation with a fourfold core is considerably lower than that of the other types of cores. Thus, the shuffle-set dislocation with the fourfold core is the most stable. The glide-set dislocation with a planar core has the highest energy and is the most unstable. As the most stable structure, the shuffle-set screw dislocation with the fourfold core was responsible for wavy slip traces observed at low temperature. [ABSTRACT FROM AUTHOR]

The scientific issue of this paper is the formation of the initial surface roughening during black silicon (b-Si) preparation by maskless SF 6 /O 2 plasma texturing. In detail, the authors investigate a novel approach whether merely substrate temperature dependent surface mechanisms and plasma particle diffusion are sufficient to theoretically obtain anisotropic etching. For that, a quasi-2D model is developed including the relevant mechanisms such as (i) etching, (ii) the deposition of the masking layer SiO x F y , (iii) plasma particle transport, and (iv) heat diffusion. Further on, a linear stability analysis is applied, firstly, to reveal theoretical conditions for anisotropic etching and, secondly, to qualitatively evaluate the impact of the model parameters on the texturing range. The evaluation shows that plasma particle diffusion along the surface is the main factor for nano-roughening. Additionally, the experimentally expected strong dependency of the texturing on the substrate temperature is confirmed and other extracted dependencies can be correlated to experimental observations. With that, a novel model is introduced explaining the initial b-Si roughening without taking into account surface removal by directed ions. [ABSTRACT FROM AUTHOR]

A practical challenge in slicing of low-cost multi-crystalline silicon (mc-Si) wafers by the fixed abrasive diamond wire sawing process is increased wire consumption due to greater wear of the diamond compared to slicing of the more expensive mono-crystalline silicon (mono-Si) wafers. In this paper, we present the results of scribing of mc-Si and mono-Si materials with two conical tip diamond indenters of the same geometry to understand the possible reasons for increased diamond wear in cutting of multi-crystalline silicon. Specifically, the scribing forces and the diamond indenter wear produced in scribing of the two silicon materials are analyzed. The results show that the forces generated in scribing of mc-Si are higher than in scribing of mono-Si. The higher forces in scribing of mc-Si are consistent with the corresponding higher tip radius of curvature (due to wear) of the diamond indenter compared to the tip radius produced in scribing of mono-Si. Scanning electron microscopy and confocal microscopy of the diamond indenters show that wear is primarily due to physical micro-fracture and blunting of the diamond. Raman spectroscopy shows evidence of stress-induced phase transformation of the diamond and the formation of compressive residual stress in the diamond. Plausible physical reasons, including the role of material inhomogeneity in mc-Si, for the wear of diamond during scribing are given. [ABSTRACT FROM AUTHOR]

This paper presents a comparative analysis of the structure and photoluminescence (PL) of Si containing dislocations introduced by thermal shock or ion implantation. To study the structure of dislocation cores and their interaction with point defects, we used a high-resolution transmission mode during in situ electron irradiation in the JEM4000EX operating at 400 kV. An appropriate PL spectrum was obtained on dislocated Si after electron irradiation by an external pulse gun operating at 350 kV. This resulted only in an increase in the D2 line intensity that correlated with the formation of metastable interstitial defects on {001}, {111}, and {113} planes near various dislocation cores during in situ electron irradiation, regardless of their types. However, the D1 line relates to a core structure of a shuffle Lomer dislocation consisting of 5/7 atomic rings, which occurs when two shuffle 60° dislocations (so-called S1 type [Pizzagalli et al., Phys. Rev. Lett. 103, 065505 (2009)]) combine with each other in intersecting {111} planes in plastically deformed Si or when an extrinsic Frank partial dislocation transforms into a perfect one in an ion-implanted layer. [ABSTRACT FROM AUTHOR]

Low-cost shortwave infrared detectors have great potential for emerging civilian night-vision applications. This paper reports the characteristics of Ge0.89Sn0.11 photodiodes monolithically grown on a Si substrate that holds great promise for those applications. At room temperature, the 500 μm diameter active area device demonstrated a longwave cutoff of 2.65 μm and a responsivity of 0.32 A/W at 2 μm, which corresponds to an external quantum efficiency of 20% without any contribution from the Ge buffer layer. The measured peak specific detectivity at 300 K and 77 K is 1.7 × 109 Jones and 4.3 × 109 Jones, respectively. The specific detectivity at 77 K is only one-order-of-magnitude lower than that of the market dominating extended-InGaAs photodiode. The detailed device analysis indicated that the 700-nm thick fully relaxed high-quality GeSn absorbing layer and the modified depletion region lead to the above-mentioned device performance. [ABSTRACT FROM AUTHOR]

The thermal rectification has potential application in the thermal management of electronics and energy saving. This paper investigates the thermal rectification in silicon nanofilm with cone cavity by the non-equilibrium molecular dynamics simulation. The results show that the thermal resistance caused by the cone cavity is on the order of 10-9 m2 KW-1. The thermal resistance of cone cavity differs averagely by about 11% from 300 K to 1100 K when the heat flow direction is turned over. The phonon wave packet dynamic simulations indicate that transverse phonons are generated by the cavity scattering of longitudinal phonon. When the phonon transport direction is reversed, the average transmission coefficient is changed by about 14% in all the frequency range and is regarded as the main reason for the thermal rectification in silicon film with cone cavity. The thermal rectification depends on the aspect ratio of the cone cavity. [ABSTRACT FROM AUTHOR]

Flexible piezoelectric thin films on polymeric substrates provide advantages in sensing, actuating, and energy harvesting applications. However, direct deposition of many inorganic piezoelectric materials such as Pb(Zrx,Ti1-x)O3 (PZT) on polymers is challenging due to the high temperature required for crystallization. This paper describes a transfer process for PZT thin films. The PZT films are first grown on a high-temperature capable substrate such as platinum-coated silicon. After crystallization, a polymeric layer is added, and the polymer-PZT combination is removed from the high-temperature substrate by etching away a release layer, with the polymer layer then becoming the substrate. The released PZT on polyimide exhibits enhanced dielectric response due to reduction in substrate clamping after removal from the rigid substrate. For Pb(Zr0.52,Ti0.48)0.98Nb0.02O3 films, release from Si increased the remanent polarization from 17.5 μC/cm2 to 26 μC/cm2. In addition, poling led to increased ferroelastic/ferroelectric realignment in the released films. At 1 kHz, the average permittivity was measured to be around 1160 after release from Si with a loss tangent below 3%. Rayleigh measurements further confirmed the correlation between diminished substrate constraint and increased domain wall mobility in the released PZT films on polymers. [ABSTRACT FROM AUTHOR]

We study the influence of phonon boundary scattering on the transport of thermal energy in semiconductor nanowires from micro to nano length scales. We use a kinetic theory model based on the Boltzmann transport equation that accurately calculates the reduction of the phonon mean free paths by considering their directional dependence and the fundamental statistical definition of the mean free path. As a result, our model does not use phenomenological formulas to account for the reduction of the phonon mean free paths due to boundary scattering. The transport of thermal energy is also fully divided into that carried by different polarizations by separating phonon group velocities and relaxation times for transverse and longitudinal phonons. We study the correctness of using frequency independent versus frequency dependent models for describing the specularity of the nanowire boundary. We also examine the validity of the assumption that phonons in the semiconductor nanowire maintain their bulk phonon dispersion relations and that modifications to the dispersion relations due to phonon confinement effects can be neglected. The thermal conductivities of silicon nanowires are calculated for different length scales and temperatures and good agreement is obtained with experiments. The theoretical results in this paper can be used to understand and quantitatively predict heat transport in nanowires, which is critical for increasing the efficiency of thermoelectric and electronic devices. [ABSTRACT FROM AUTHOR]