Point Defects In Silicon Research Articles

The effect of charge and spin state on the Infrared spectra and hyperfine coupling constants of point defects in Silicon

The effect of the charge of a point defect on the infrared spectrum and the hyperfine coupling constants is discussed with reference to the VO defect in silicon. Five charge states have been considered, from +2e to −2e. Calculations are performed by using a local Gaussian type basis set and the B3LYP hybrid functional. The dominant peak in the IR spectrum increases linearly from 708 cm−1 (+2 charge), to 904 cm−1 (−2 charge). The intensity decreases from 4073 to 1727 km/mol, as a consequence of the reduced polarity of the Si-O bond. Also the hyperfine constants differ by large percentages along the series. Although limited to a single defect, the present study shows that both the IR and EPR techniques are able to discriminate the charge state of the defect, also in the cases in which more than one charge state is present in the same sample.

A single silicon colour centre resolved

Isolated point defects in silicon that emit light at telecom wavelengths could help accelerate the development of quantum information technologies using commercial platforms.

A comprehensive theoretical picture of E centers in silicon: From optical properties to vacancy-mediated dopant diffusion

Among the common vacancy-related point defects in silicon, the E center is one of the most prominent due to its degrading effect in silicon-based technology. Even though it has been the subject of extensive experimental and theoretical studies, a comprehensive theoretical model capable of reproducing the experimental evidence for all three dopants (P, As, and Sb) is still missing. Guided by a Jahn-Teller model, we are able to reproduce the absorption bands and the transition probability between equivalent geometries of the defect at low temperatures by including many-body-perturbation corrections based on the GW approximation on top of the density functional theory. At higher temperatures, vacancies become mobile centers, enabling the reorientation of the whole defect and contributing to the dopant diffusion. The underlying mechanisms of the vacancy-mediated dopant diffusion are revisited, characterizing the activation energies of such technologically relevant processes and obtaining quantitative results in good agreement with experiment.

Oxygen Precipitation in Highly Doped Silicon Substrates

This paper reviews oxygen precipitation in heavily arsenic-doped silicon. A wide arsenic concentration range is explored, from 3 × 1018 cm−3 to 4 × 1019 cm−3. A precipitation retardation effect is observed in the arsenic doped samples when the dopant concentration is higher than 1.7 × 1019 cm−3 compared with lightly doped samples having the same initial oxygen content and grown under similar conditions. The oxygen precipitate density in the heavily arsenic-doped samples is uniform along the wafer radius, with no rings or cores, contrary to what is commonly observed in lightly doped samples grown with similar V/G values. This finding is discussed by considering the role played by vacancies in the formation of oxygen precipitates and the impact of the arsenic concentration on the equilibrium concentration of point defects in silicon, deduced from the experimentally observed voids revealed as light-scattering surface defects in polished wafers.

(Invited) Oxygen Precipitation in Highly Doped Silicon Substrates

This paper reviews oxygen precipitation in heavily arsenic-doped silicon. A wide arsenic concentration range is explored, from 3 × 1018 cm-3 to 4 × 1019 cm-3. A precipitation retardation effect is observed in the arsenic doped samples when the dopant concentration is higher than 1.7x1019 cm-3 compared with lightly doped samples having the same initial oxygen content and grown under similar conditions. The oxygen precipitate density in the heavily arsenic-doped samples is uniform along the wafer radius, with no rings or cores, contrary to what is commonly observed in lightly doped samples grown with similar V/G values. This finding is discussed by considering the role played by vacancies in the formation of oxygen precipitates and the impact of the arsenic concentration on the equilibrium concentration of point defects in silicon, deduced from the experimentally observed voids revealed as light-scattering surface defects in polished wafers.

(Invited) Oxygen Precipitation in Highly Doped Silicon Substrates

Heavily doped silicon substrates are widely used for the fabrication of discrete devices for power applications. The basic wafer template is generally composed of an epitaxial layer over a heavily doped silicon substrate whose dopant type and resistivity vary depending on the final device characteristics but, in either case of P- and N-type substrates, the demand is more and more oriented towards very low resistivity ranges, such as 0.5-5 mΩ·cm, in order to minimize the substrate contribution to the transistor drain-source resistance. Furthermore, the continuous effort to reduce manufacturing costs is moving discrete device fabrication from 100-150 mm in wafer diameter to 200 mm and even to 300 mm. Often a vertical device structure is chosen, where the electric current flows through the entire wafer thickness, therefore the properties of the wafer bulk affect the device performance and the bulk defectivity level have to be understood and controlled carefully. This paper focuses on the microdefect formation in heavily donor-doped silicon, and, in particular, on the behaviour of oxygen precipitation in heavily arsenic-doped silicon. A challenge when dealing with experimental investigations on the behaviour of oxygen in heavily donor-doped silicon is the difficulty of decoupling the oxygen level and the dopant concentration level during crystal growth. Differently from the case of lightly doped or even of heavily boron-doped crystals, during the growth of silicon crystals heavily doped with volatile donors, such as arsenic, antimony or red phosphorus, a strong interaction is unavoidably observed between oxygen and dopant evaporation, leading to a certain degree of correlation between the resulting oxygen level and the dopant concentration level. To overcome this problem, a set of lightly doped silicon samples with similar initial oxygen concentration and growth conditions are included in this study, to discriminate the impact of the oxygen concentration and the impact of the dopant concentration. A wide arsenic concentration range is explored, from 3 × 1018 cm-3 to 4 × 1019 cm-3. The oxygen precipitation is characterized after a thermal cycle of 4 h at 800°C for nuclei stabilization + 16 h at 1000°C for nuclei growth. Oxide precipitates (BMD) are counted under microscope on the cleaved sample surface after preferential etching. A precipitation retardation effect is observed in the arsenic doped samples when the dopant concentration is higher than 1.7x1019 cm-3 compared with lightly doped samples having the same initial oxygen content and grown under similar conditions. The BMD density in the arsenic-doped samples is uniform along the radius, with no rings or cores, contrary to what is commonly observed in lightly doped samples grown with similar V/G values. This finding is discussed by considering the role played by vacancies in the formation of oxygen precipitates and the impact of the arsenic concentration on the equilibrium concentration of point defects in silicon, deduced from the experimentally observed voids revealed as light-scattering surface defects in polished wafers. For arsenic-doped wafers, the voids count first increases but then – at [As] > 1.7x1019 cm-3 - sharply drops. This dependence of counts on concentration can be explained by assuming that the substitutional dopant Ms can trap vacancies by forming vacancy-impurity complexes VMs (trapped vacancies) while a small fraction of interstitial dopant Mi acts as trapped self-interstitials. The net amount of incorporated vacancy species includes the initial concentration difference [VMs] – [Mi]. The VMs species – assumed of the same positive charge state as Ms - provide a dominant contribution at lower [Ms] whereas the negatively charged Mi species dominate at higher [Ms]. Accordingly, the net vacancy concentration increases at first, but then decreases and tends toward zero [1], reducing the number of vacancies available for void formation as well as for assisting BMD nucleation. [1] V. V. Voronkov, R. Falster, M. Porrini, and J. Duchini, Phys. Status Solidi A 209, 1898 (2012)

Diffusion and Point Defects in Elemental Semiconductors

Elemental semiconductors play an important role in high-technology equipment used in industry and everyday life. The first transistors were made in the 1950ies of germanium. Later silicon took over because its electronic band-gap is larger. Nowadays, germanium is the base material mainly for γ-radiation detectors. Silicon is the most important semiconductor for the fabrication of solid-state electronic devices (memory chips, processors chips, ...) in computers, cellphones, smartphones. Silicon is also important for photovoltaic devices of energy production.Diffusion is a key process in the fabrication of semiconductor devices. This chapter deals with diffusion and point defects in silicon and germanium. It aims at making the reader familiar with the present understanding rather than painstakingly presenting all diffusion data available a good deal of which may be found in a data collection by Stolwijk and Bracht [1], in the author’s textbook [2], and in recent review papers by Bracht [3, 4]. We mainly review self-diffusion, diffusion of doping elements, oxygen diffusion, and diffusion modes of hybrid foreign elements in elemental semiconductors.Self-diffusion in elemental semiconductors is a very slow process compared to metals. One of the reasons is that the equilibrium concentrations of vacancies and self-interstitials are low. In contrast to metals, point defects in semiconductors exist in neutral and in charged states. The concentrations of charged point defects are therefore affected by doping [2 - 4].

Optical properties of an ensemble of G-centers in silicon

We addressed the carrier dynamics in so-called G-centers in silicon (consisting of substitutional-interstitial carbon pairs interacting with interstitial silicons) obtained via ion implantation into a silicon-on-insulator wafer. For this point defect in silicon emitting in the telecommunication wavelength range, we unravel the recombination dynamics by time-resolved photoluminescence spectroscopy. More specifically, we performed detailed photoluminescence experiments as a function of excitation energy, incident power, irradiation fluence and temperature in order to study the impact of radiative and non-radiative recombination channels on the spectrum, yield and lifetime of G-centers. The sharp line emitting at 969 meV ($\sim$1280 nm) and the broad asymmetric sideband developing at lower energy share the same recombination dynamics as shown by time-resolved experiments performed selectively on each spectral component. This feature accounts for the common origin of the two emission bands which are unambiguously attributed to the zero-phonon line and to the corresponding phonon sideband. In the framework of the Huang-Rhys theory with non-perturbative calculations, we reach an estimation of 1.6$\pm$0.1 $\angstrom$ for the spatial extension of the electronic wave function in the G-center. The radiative recombination time measured at low temperature lies in the 6 ns-range. The estimation of both radiative and non-radiative recombination rates as a function of temperature further demonstrate a constant radiative lifetime. Finally, although G-centers are shallow levels in silicon, we find a value of the Debye-Waller factor comparable to deep levels in wide-bandgap materials. Our results point out the potential of G-centers as a solid-state light source to be integrated into opto-electronic devices within a common silicon platform.

Reduced oxygen precipitation in heavily arsenic‐doped Cz‐silicon crystals

AbstractOxygen precipitation in heavily arsenic doped Czochralski silicon is investigated for a wide dopant concentration range (from 3 × 1018 cm–3 to 4 × 1019 cm–3) and it is compared with that observed in lightly doped silicon having similar initial oxygen concentration. A lower density of oxide precipitates after an anneal of 4 h at 800 °C followed by 16 h at 1000 °C is measured in the case of arsenic doped samples, in comparison to lightly doped ones, when the dopant concentration exceeds 1.6 × 1019 cm–3. In addition, no radial bands (rings) of precipitation are observed in arsenic‐doped samples, contrary to lightly doped samples grown at the same V/G (ratio between pull rate V and axial thermal gradient G). These findings are explained by considering the role played by vacancies in the formation of oxygen precipitates and the impact of the arsenic concentration on the total concentration of point defects in silicon. Data obtained by computer simulation of microdefect formation in silicon are also presented in support of this explanation. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effects of Spin-Dependent Recombination and EPR Spectroscopy of the Excited Triplet States of Point Defects in Silicon

Highly sensitive methods of the detection of the electron paramagnetic resonance (EPR) spectra based on the spin-dependent microwave photoconductivity were applied for investigation of the point defects in silicon. The specific features and properties of the excited triplet (spin S = 1) states of defects responsible for spin-dependent recombination of photo excited carriers are considered. The main attention is given to study such defects as oxygen + vacancy complexes and carbon related centers dominantly produced by irradiation.

Influence of the ab-initio calculation parameters on prediction of energy of point defects in silicon

Point defects play a key role in many microelectronics technologies. Knowledge of the properties of point defects and characteristics of their behavior during ion-beam synthesis of microstructures for use in silicon devices allows one to optimize the conditions of their production, improve their quality and the electronic properties. In this situation, of valuable help in studying the properties of point defects is numerical modeling, especially with the use of quantum mechanical methods based on density functional theory approach. The paper describes a systematic study of the effect of various quantum–mechanical simulation approximations on the calculated energy parameters of defects as applied to simple point defects in silicon. We demonstrate that the choice of the form of the exchange–correlation functional has the strongest effect on the predicted defect formation energy, whereas the variation of the other considered approximations is of secondary importance for simulation predictions.

Influence of the ab initio Calculation Parameters on Prediction of Energy of Point Defects in Silicon

Point defects play a key role in many of the microelectronics device technologies. Knowledge of the properties of point defects and characteristics of their behavior during radiative synthesis of microstructures for use in silicon devices allows one to optimize the conditions of their production, improve their quality and improve the electronic properties. To a large extent this was due to the complexity of measuring the parameters of point defects. In this situation, of valuable help in studying the properties of point defects is numerical modeling, especially with the use of quantum mechanical methods based on density functional theory approach. The paper describes a systematic study of the effect of various quantum − mechanical simulation approximations influence the calculated energy parameters of defects as applied to simple point defects in silicon. We have demonstrated that the choice of the form of the exchange − correlation functional has the strongest effect on the predicted defect formation energy, whereas the variation of the other considered approximations is of secondary importance for simulation predictions.

Diffusion of point defects in crystalline silicon using the kinetic activation-relaxation technique method

We study point-defect diffusion in crystalline silicon using the kinetic activation-relaxation technique (k-ART), an off-lattice kinetic Monte Carlo method with on-the-fly catalog building capabilities based on the activation-relaxation technique (ART nouveau), coupled to the standard Stillinger-Weber potential. We focus more particularly on the evolution of crystalline cells with one to four vacancies and one to four interstitials in order to provide a detailed picture of both the atomistic diffusion mechanisms and overall kinetics. We show formation energies, activation barriers for the ground state of all eight systems, and migration barriers for those systems that diffuse. Additionally, we characterize diffusion paths and special configurations such as dumbbell complex, di-interstitial (IV-pair+2I) superdiffuser, tetrahedral vacancy complex, and more. This study points to an unsuspected dynamical richness even for this apparently simple system that can only be uncovered by exhaustive and systematic approaches such as the kinetic activation-relaxation technique.

Features of the uniaxial elastic deformation of X-ray-irradiated p-Si crystals

Changes in the conductivity of p-Si single-crystals irradiated at room temperature during their mechanical compression and stress relief are studied. It is shown that irradiation is accompanied by the generation of point defects in silicon, which play the role of stoppers for dislocation motion. The effect of “radiation memory” in “electronic” silicon crystals is detected.

045 Si単結晶中の点欠陥形成に与えるドーパントの影響に関する第一原理解析

045 Si単結晶中の点欠陥形成に与えるドーパントの影響に関する第一原理解析

Modeling platinum diffusion in silicon

Simulations based on diffusion-limited reaction rates were able for the first time to reproduce platinum profiles in silicon for in-diffusion in a wide temperature range from 730 to 950 °C and out-diffusion associated with the ramping-down of the temperature at the end of an industrial diffusion process at 830 °C. A rigorous analysis of the out-diffusion and short-time in-diffusion profiles allowed narrowing down the parameter range for the intrinsic point defects in silicon.

Enhanced von Weizsäcker Wang-Govind-Carter kinetic energy density functional for semiconductors.

We propose a new form of orbital-free (OF) kinetic energy density functional (KEDF) for semiconductors that is based on the Wang-Govind-Carter (WGC99) nonlocal KEDF. We enhance within the latter the semi-local von Weizsäcker KEDF term, which is exact for a single orbital. The enhancement factor we introduce is related to the extent to which the electron density is localized. The accuracy of the new KEDF is benchmarked against Kohn-Sham density functional theory (KSDFT) by comparing predicted energy differences between phases, equilibrium volumes, and bulk moduli for various semiconductors, along with metal-insulator phase transition pressures. We also compare point defect and (100) surface energies in silicon for a broad test of its applicability. This new KEDF accurately reproduces the exact non-interacting kinetic energy of KSDFT with only one additional adjustable parameter beyond the three parameters in the WGC99 KEDF; it exhibits good transferability between semiconducting to metallic silicon phases and between various III-V semiconductors without parameter adjustment. Overall, this KEDF is more accurate than previously proposed OF KEDFs (e.g., the Huang-Carter (HC) KEDF) for semiconductors, while the computational efficiency remains at the level of the WGC99 KEDF (several hundred times faster than the HC KEDF). This accurate, fast, and transferable new KEDF holds considerable promise for large-scale OFDFT simulations of metallic through semiconducting materials.

Properties of Point Defects in Silicon: New Results after a Long-Time Debate

The contributions of vacancies and self-interstitials to silicon (Si) self-diffusion are a matter of debate since many years. These native defects are involved in dopant diffusion and the formation of defect clusters and thus influence many processes that take place during Si single crystal growth and the fabrication of silicon based electronic devices. Considering their relevance it is remarkable that present data about the properties of native point defects in Si are still limited and controversy. This work reports recent results on the properties of native point defects in silicon deduced from self-diffusion experiments below 850°C. The temperature dependence of silicon self-diffusion is accurately described by contributions due to vacancies and self-interstitials assuming temperature dependent vacancy properties. The concept of vacancies whose thermodynamic properties change with temperature solves the inconsistency between self-and dopant diffusion in Si but further experiments are required to verify this concept and to prove its relevance for other material systems.

Coordination-driven magnetic-to-nonmagnetic transition in manganese-doped silicon clusters

The interaction of a single manganese impurity with silicon is analyzed in a combined experimental and theoretical study of the electronic, magnetic, and structural properties of manganese-doped silicon clusters. The structural transition from exohedral to endohedral doping coincides with 3$d$ electron delocalization and a quenching of high-spin states. For all geometric structures investigated, we find a correlation of the magnetic moment with the manganese coordination number and nearest-neighbor distance. This observation can be generalized to manganese point defects in bulk silicon, whose magnetic moments fall within the observed magnetic-to-nonmagnetic transition, and therefore react very sensitively to changes in the local geometry. The results indicate that high-spin states in manganese-doped silicon could be stabilized by an appropriate lattice expansion.

Electronic Structure and van der Waals Interactions in the Stability and Mobility of Point Defects in Semiconductors

We study the role of electronic structure (band gaps) and long-range van der Waals (vdW) interactions on the stability and mobility of point defects in silicon and heavier semiconductors. Density functional theory calculations with hybrid functionals that contain part of the Hartree-Fock exchange energy are essential to achieve a reasonable description of defect electronic levels, leading to accurate defect formation energies. However, these functionals significantly overestimate the experimental migration barriers. The inclusion of screened vdW interactions further improves the description of defect formation energies, significantly changes the barrier geometries, and brings migration barrier heights into close agreement with experimental values. These results suggest that hybrid functionals with vdW interactions can be successfully used for predictions in a broad range of materials in which the correct description of both the electronic structure and the long-range electron correlation is essential.