Point Defects In Silicon Research Articles

Role of screening in the density functional applied to transition-metal defects in semiconductors

We study selected transition metal related point defects in silicon and silicon carbide semiconductors by a range separated hybrid density functional (HSE06). We find that HSE06 does not fulfill the generalized Koopmans' Theorem for every defect which is due to the self-interaction error in the functional in such cases. Restoring the so-called generalized Koopmans' Condition with a simple correction in the functional can eliminate this error, and brings the calculated charge transition levels remarkably close to the experimental data as well as to the calculated quasi-particle levels from many-body perturbation theory.

Impact of rapid thermal annealing temperature on non-metallised polycrystalline silicon thin-film diodes on glass

A rapid thermal annealing (RTA) process is performed to activate the dopants and anneal point defects in planar polycrystalline silicon (poly-Si) thin-film solar cell diodes on glass. The impact of the RTA peak temperature on the open-circuit voltage (Voc), the sheet resistance and the doping profiles of the non-metallised samples was investigated. An annealing temperature of about 1000°C was found to give the highest Voc and the lowest sheet resistance. The doping concentration was measured using the electrochemical capacitance voltage (ECV) method. The doping concentration was found to increase with increasing RTA temperature, before it decreased at high temperature. The junction depth was found to move away from the glass-side with increasing annealing temperature. The sheet resistances were calculated based on the ECV doping profiles and were found to have a trend similar to the experimental values obtained by the four-point probe method. The highest average Voc obtained in this work is 471mV and it corresponds to the lowest sheet resistance.

Impurity engineering of Czochralski silicon

Microelectronic devices with high integration level and functional complexity are always requiring larger diameter and more perfect Czochralski (CZ) silicon wafers. Therefore, the defects, playing the key role in the quality control of silicon materials, have to be well controlled during crystal growth and device fabrication. Co-doping nitrogen (N), germanium (Ge) or carbon (C) into CZ silicon to control defect dynamics and to change defect evolution, so-called “impurity engineering”, has been developed in recent years, and has been widely applied in the fabrication of higher quality CZ silicon used for microelectronics nowadays. This article is to present an overview of the current status of impurity engineering in CZ silicon, based on the co-doping technologies of N, Ge and C. The fundamental properties of these three co-dopants and their interaction with point defects in CZ silicon are firstly introduced. The bulk of the article is focused on the effects of co-dopants on the formation of oxygen precipitates related to internal gettering (IG) of devices for metal contaminants, and voids associated with the gate oxide integrity (GOI) of devices in CZ silicon. Finally, the improvement of CZ silicon mechanical strength by co-doping technology is described.

Ab initio modelling of boron related defects in amorphous silicon

AbstractWe have modeled boron related point defects in amorphous silicon, using an ab initio method, the Density functional theory‐pseudopotential code Aimpro. The boron atoms were embedded in 64 atom amorphous silicon cubic supercells. The calculations were performed using boron defects in 15 different supercells. These supercells were developed using a modified Wooten‐Winer‐Weaire bond switching mechanism. In average, the properties of the 15 supercells agree with the observed radial and bond angle distributions, as well the electronic and vibrational density of states and Raman spectra. In amorphous silicon it has been very hard to find real self‐interstitials, since for almost all the tested configurations, the amorphous lattice relaxes overall. We found that substitutional boron prefers to be 4‐fold coordinated. We find also an intrinsic hole‐trap in the non‐doped amorphous lattice, which may explain the low efficiency of boron doping. The local vibrational modes are, in average, higher than the correspondent crystalline values (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Ab initioEPR parameters for dangling-bond defect complexes in silicon: Effect of Jahn-Teller distortion

A dangling bond (db) is an important point defect in silicon. It is realized in crystalline silicon by defect complexes of the monovacancy $V$ with impurities. In this work, we present spin-polarized density-functional theory calculations of EPR parameters ($g$ and hyperfine tensors) within the GIPAW formalism for two kinds of db defect complexes. The first class characterizes chemically saturated db systems, where three of the four dangling bonds of the isolated vacancy are saturated by hydrogen ($V{H}_{3}$) or hydrogen and oxygen (hydrogen-oxygen complex, $VOH$). The second kind of db consists of systems with a Jahn-Teller distortion, where the vacancy includes either a substitutional phosphorus atom (the $E$ center, $VP$) or a single hydrogen atom ($VH$). For all systems we obtain excellent agreement with available experimental data, and we are therefore able to quantify the effect of the Jahn-Teller distortion on the EPR parameters. Furthermore we study the influence of strain to obtain further insights into the structural and electronic characteristics of the considered defects.

Imaging of Metastable Defects in Silicon

Photoluminescence imaging is able to provide quantitative information about carrier lifetime in silicon wafers. Recently, this technique has been applied to measure the distribution of iron and chromium point defects in p-type silicon. In this paper, we summarize the state of the art and extend the impurity analysis by photoluminescence imaging with the detection of the boron-oxygen defect. Solar cells from p-type Czochralski silicon material are mostly limited by this defect, but its impact may also be significant for multicrystalline silicon. For the presence of several metastable defect species, we demonstrate the preparation of a specific state of the metastable defects with appropriate conditions for temperature and illumination and show that the respective impurity concentrations can be determined in parallel. We complete the analysis by discussing the effects of lateral carrier diffusion on the measurement result.

First principle study of the thermal conductance in graphene nanoribbon with vacancy and substitutional silicon defects

The thermal conductance in graphene nanoribbon with a vacancy or silicon point defect is investigated by nonequilibrium Green’s function (NEGF) formalism combined with first-principles calculations of density-functional theory with local density approximation. The thermal conductance is very sensitive to the position of the vacancy defect, while insensitive to the position of silicon defect. A vacancy defect situated at the center of the nanoribbon generates a saddlelike surface, which greatly reduces the thermal conductance by strong scattering to all phonon modes; while an edge vacancy defect only results in a further reconstruction of the edge and slightly reduces the thermal conductance.

Continuum simulation of solid phase epitaxial regrowth of amorphized silicon including most advanced physical interactions

AbstractSolid‐phase‐epitaxial regrowth (SPER) of Si amorphized by ion implantation is considered as a potential solution for the fabrication of highly‐activated ultra‐shallow junctions for future technology nodes of Si CMOS devices. In the frame of 32 and 22 nm technologies node development, SPER occurs after amorphizing implantations used in source/drain regions. To get an accurate simulation of dopant activation and junction depth position, a suitable continuum SPER model, implemented into a commercial simulator, is now mandatory. This TCAD model must consider the different physical effects associated with SPER: silicon regrowth rate, dopants redistribution snow plough effect, and interaction with silicon point defects. In this work, using a previously established model, we have implemented an improved physically based model for SPER and, several formulations have been developed to enable a robust/accurate modeling of the recrystallization velocity. It takes into account the direct interaction between amorphous/crystalline interface kinetics and point defects, and a regrowth rate dependent on temperature. Simulation results of dopant concentration profiles are in good agreement with experimental data and can provide important insight for optimizing the bulk silicon process as well in one dimension as two dimensions.

Simulation of silicon diffusion in GaAs

The simulation of coupled diffusion of silicon atoms and point defects in GaAs has been carried out for diffusion at the temperatures of 1000 and 850 °C. The amphoteric behavior of silicon atoms in GaAs has been taken into account in the investigation of high concentration diffusion from silicon layer deposited on GaAs substrate. The calculated dopant profiles agree well with the experimental ones and they confirm the adequacy of the model of silicon diffusion used for simulation. A comparison with the experimental data has enabled this work to obtain the parameters of silicon effective diffusivity and other values describing high concentration silicon diffusion in GaAs.

Imaging of chromium point defects in p-type silicon

In this work a method for the spatially resolved detection of the Cr point defect distribution in p-type silicon based on photoluminescence imaging was developed and successfully applied on monocrystalline and multicrystalline wafers. Chromium was identified by its metastable defect configuration and the association time during the formation of chromium–boron pairs. Further defects which could influence the Cr concentration determination have been studied and their influence was suppressed. For a quantitative evaluation of the chromium concentration, the knowledge of exact values of defect parameters such as energy level and capture cross sections for electrons and holes for both Cr states is essential. From the doping dependence of the lifetime, published defect parameters have been analyzed and adjusted slightly in order to explain experimental results. With these parameters reasonable averaged Cr point defect concentrations have been determined for different monocrystalline and multicrystalline samples. Furthermore, space-resolved images of the Cr point defect concentration could be acquired, permitting study of the distribution within a multicrystalline sample with respect to grains and grain boundaries or dislocation clusters.

Gedanken experiment on point defects in unidirectional solidified single crystalline silicon with no dislocations

A gedanken experiment was carried out to investigate point defects formed in unidirectional solidified single crystalline silicon for solar cells, ignoring dislocations in crystals. A transient global model was used to obtain the solution of a thermal field within the entire furnace. Then, based on the global solution of heat transfer, diffusion and recombination of vacancies and interstitials were calculated by the Finite Volume Method (FVM). It was found that vacancies became dominant as the melt was solidified and solidification time was reduced. The ratio between growth rate V g and temperature gradient in growth direction G was also analyzed. The results revealed that growth rate is the key factor affecting point defects in single crystalline silicon with no dislocations.

Probing the Behaviors of Point Defects in Silicon and Germanium Using Isotope Superlattices

In order to probe the fundamental behaviors of point defects in silicon and germanium, we studied the self-diffusion using isotope superlattices. In ion-implanted germanium, vacancies are in thermal equilibrium and transient enhanced diffusion is not present under the experimental conditions employed in this study. In contrast, silicon self-interstitials are supersaturated in ion-implanted silicon and the self-interstitial concentration is going down to the thermal equilibrium value toward the surface.

Probing the Behaviors of Point Defects in Silicon and Germanium Using Isotope Superlattices

not Available.

Increased Phonon Scattering by Nanograins and Point Defects in Nanostructured Silicon with a Low Concentration of Germanium

The mechanism for phonon scattering by nanostructures and by point defects in nanostructured silicon (Si) and the silicon germanium (Ge) alloy and their thermoelectric properties are investigated. We found that the thermal conductivity is reduced by a factor of 10 in nanostructured Si in comparison with bulk crystalline Si. However, nanosize interfaces are not as effective as point defects in scattering phonons with wavelengths shorter than 1 nm. We further found that a 5 at. % Ge replacing Si is very efficient in scattering phonons shorter than 1 nm, resulting in a further thermal conductivity reduction by a factor of 2, thereby leading to a thermoelectric figure of merit 0.95 for Si95Ge5, similar to that of large grained Si80Ge20 alloys.

Interstitial-based boron diffusion dynamics in amorphous silicon

Using density-functional theory calculations we identified an interstitial-based fast boron diffusion mechanism in amorphous silicon. We found that interstitial-like point defects, omnipresent in as-implanted silicon, to be very stable in an amorphous network and can form highly mobile pair with Boron atoms. The transient existence of such point defects in amorphous silicon is suggested to play an important role in boron diffusion. We found the activation energy for this pathway to be 2.73 eV, in good agreement with experimental results. In addition, this mechanism is consistent with the experimentally reported transient and concentration-dependent features of boron diffusion in amorphous silicon.

Correlation between self-diffusion in Si and the migration mechanisms of vacancies and self-interstitials: An atomistic study

The migration of point defects in silicon and the corresponding atomic mobility are investigated by comprehensive classical molecular-dynamics simulations using the Stillinger-Weber potential and the Tersoff potential. In contrast to most of the previous studies both the point defect diffusivity and the self-diffusion coefficient per defect are calculated separately so that the diffusion-correlation factor can be determined. Simulations with both the Stillinger-Weber and the Tersoff potential show that vacancy migration is characterized by the transformation of the tetrahedral vacancy to the split vacancy and vice versa and the diffusion-correlation factor ${f}_{V}$ is about 0.5. This value was also derived by the statistical diffusion theory under the assumption of the same migration mechanism. The mechanisms of self-interstitial migration are more complex. The detailed study, including a visual analysis and investigations with the nudged elastic band method, reveals a variety of transformations between different self-interstitial configurations. Molecular-dynamics simulations using the Stillinger-Weber potential show that the self-interstitial migration is dominated by a dumbbell mechanism, whereas in the case of the Tersoff potential the interstitialcy mechanism prevails. The corresponding values of the correlation factor ${f}_{I}$ are different, namely, 0.59 and 0.69 for the dumbbell and the interstitialcy mechanisms, respectively. The latter value is nearly equal to that obtained by the statistical theory which assumes the interstitialcy mechanism. Recent analysis of experimental results demonstrated that in the framework of state-of-the-art diffusion and reaction models the best interpretation of point defect data can be given by assuming ${f}_{I}\ensuremath{\approx}0.6$. The comparison with the present atomistic study leads to the conclusion that the self-interstitial migration in Si should be governed by a dumbbell mechanism.

Rapid Thermal Processing and the Control of Oxygen Precipitation Behaviour in Silicon Wafers

The use of Rapid Thermal Processing to install lattice vacancy profiles into silicon wafers for the purpose of forming a template for the nucleation and ideal control of oxygen precipitation has become an important materials engineering tool for the microelectronics industry. This paper reviews the principles of the technique and the precise materials/defect engineering that it engenders. It furthermore discusses what has been learned regarding the elusive properties of the intrinsic point defects in silicon through studies of the distributions of vacancies created by use of the technique. Also discussed are recent discoveries about the critical role of the other intrinsic point defect, the self-interstitial and the development of oxygen precipitates and their distributions post-nucleation and the critical importance of what has become to be called the “ninja transformation” in the switching-on of gettering efficiency of oxygen precipitate systems.

In honour of Prof. Dr. Dr. h.c. Alfred Seeger on the occasion of his 80th birthday

AbstractOn 31 August 2007, Alfred Seeger, Emeritus Professor of Solid State Physics at the University of Stuttgart and former Director at the Max‐Planck‐Institut für Metallforschung in Stuttgart will celebrate his 80th birthday. This is a perfect occasion for the Editors and the Staff of physica status solidi to express their deepest appreciation and gratitude to an eminent scientist, who has shaped our journal as a Founding Editor, a member of the Editorial Board, as well as an author and referee for more than 40 years!Alfred Seeger was born in Stuttgart in 1927 and studied Physics at the Technische Hochschule Stuttgart from 1946 to 1949. He received his Ph.D. in March 1951 at the tender age of 24 and, following post‐doctoral stays in Bristol and Cambridge, obtained the newly founded Chair of Solid State Physics in Stuttgart in 1959. In 1965, he also became the Director of the Institute of Physics at the Max‐Planck‐Institut für Metallforschung. Alfred Seeger's scientific oeuvre includes more than 650 publications in international scientific journals, which so far have been cited more than 13000 times. In recognition of his important contributions to solid state physics, Alfred Seeger has received numerous awards and honours, e.g. the Gold Medal of the Japanese Institute of Metals and the German–South African Alexander von Humboldt Prize.Almost in parallel to his outstanding career as an internationally renowned scientist, Alfred Seeger also has had a strong influence on the fate and on the scientific impact of physica status solidi ever since he agreed to become a Founding Editor of the journal in 1960. We all value him as a very productive and reliable member of the Editorial Board, always willing to help and giving honest and critical advice when needed. Most impressive are also his scientific contributions to the journal. Starting from three papers published in Volume 1 of physica status solidi, Alfred Seeger has contributed on the average four articles per year between 1961 and 1971, and about one article per year from 1972 to 2004. These sum up to a total of 79 papers published in physica status solidi so far with Alfred Seeger as first author or as a co‐author, which have been cited more than 2500 times as up to now. The two contributions with the highest impact are the 1968 paper of Seeger and Chik on “Diffusion Mechanisms and Point Defects in Silicon and Germanium” [phys. stat. sol. 29, 455 (1968)] and the article on “Interpretation of Self‐Diffusion and Vacancy Properties in Copper” [Mehrer and Seeger, phys. stat. sol. 35, 313 (1969)].On behalf of all Editors of physica status solidi, the entire editorial staff, as well as many friends and colleagues, I personally want to thank Alfred Seeger for nearly 50 years of invaluable support of our journal as an Editor and a scientist. We all wish him good health and many more productive years to come. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Cobalt related defect levels in silicon analyzed by temperature- and injection-dependent lifetime spectroscopy

Temperature- and injection-dependent lifetime spectroscopy (TIDLS) as a method to characterize point defects in silicon with several energy levels is demonstrated. An intentionally cobalt-contaminated p-type wafer was investigated by means of lifetime measurements performed at different temperatures up to 151°C. Two defect energy levels were required to model the lifetime curves on basis of the Shockley-Read-Hall statistics. The detailed analysis is based on the determination of the recently introduced defect parameter solution surface (DPSS) in order to extract the underlying defect parameters. A unique solution has been found for a deep defect level located in the upper band gap half with an energy depth of EC−Et=0.38±0.01eV, with a corresponding ratio of capture cross sections k=σn∕σp=0.16 within the interval of uncertainty of 0.06–0.69. Additionally, a deep donor level in the lower band gap half known from the literature could be assigned to a second energy level within the DPSS analysis at Et−EV=0.41...

First Principles Analysis of Formation Energy of Point Defects and Voids in Silicon Crystals during the Cooling Process of Czochralski Method (Dopant Type and Concentration Dependence)

The effects of p-type (B) or n-type (P or As) dopant concentration on the formation energy EF of point defects in silicon (Si) crystals during the cooling process of the Czochralski (CZ) method were studied by first principles analysis. EF of several charge states of vacancy (V) and interstitial Si (I) was calculated as a function of the Fermi level. EF of the most stable state of V and I in Si crystals was estimated by considering the dependence of the Fermi level on crystal temperature. The V concentration was found to decrease in p-type but to increase in n-type Si crystals when dopant concentration was higher than about 1×1019 atoms/cm3. This explains the reported experimental results for void formation behavior in Si crystals, i.e., void formation is suppressed by an increase in p-type dopant concentration above about 1×1019 atoms/cm3, but is enhanced by an increase in n-type dopant concentration to about 3×1019 atoms/cm3. Other calculations showed that, at the initial stage of void formation, the reduction of the total energy of stable P-Vn or As-Vn complex formation was greater than that of stable Vn complex formation from isolated P or As atoms and vacancies.