Micro-defect effects on minority carrier lifetime in high purity dislocation-free silicon single crystals (original) (raw)
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Effects of Dislocations on Minority Carrier Lifetime in Dislocated Float Zone Silicon
We present a correlation of Microwave Photoconductance Decay minority carrier lifetime with dislocation density in high purity Float Zone silicon. Electron Beam Induced Current (EBIC) images were carefully aligned to lifetime maps and depth profiling of individual defect electrical activity was done by varying the bias of Schottky diodes. The data presented provides a relationship between lifetime variations and EBIC contrast, based on dislocation density and impurity decoration in the near surface zone. NREL/BK-520-32717 August 2002 12th Workshop on Crystalline Silicon Solar Cell Materials and Processes View publication stats View publication stats
Stress and doping impact on intrinsic point defect behavior in growing single crystal silicon
For the mass-production of 450 mm-diameter defect-free Si crystals, one has to take into account the impact of thermal stress on intrinsic point defect properties and behavior during single crystal growth from a melt. Very recently, first experimental evidence was published that the compressive thermal stress near the melt/solid interface makes a growing 300 mm diameter Czochralski Si crystal more vacancy-rich. In order to explain these experimental results quantitatively, the dependence of the formation enthalpies of the vacancy (V) and the self-interstitial (I) on compressive plane stress was determined using density functional theory (DFT) based calculations. It is found that compressive plane stress gives a higher stress dependence of the so-called "Voronkov criterion" compared to isotropic stress. The calculated plane stress dependence is in excellent agreement with the published experimental values and should be taken into account in the development of pulling processes for 450 mm diameter defect-free Si crystals. Also, the mechanisms behind the experimentally observed impact of the type and concentration of substitutional dopants on intrinsic point defect behavior and formation of grown-in defects are clarified. On the basis of the DFT calculated results, an appropriate model of intrinsic point defect behavior in heavily doped Si is proposed. (i) The incorporated total V and I concentrations at the melting point depend on the types and concentrations of dopants. (ii) Most of the total V and I concentrations contribute to Frenkel pair recombination during Si crystal growth at temperatures much higher than those to form grown-in intrinsic point defect clusters. The Voronkov model, while taking into account the present improvements, clearly explains all reported experimental results on grown-in defects for heavily doped Si. The most important remaining problems with respect to intrinsic point defect behavior and properties during single crystal growth from a melt are also discussed.
Microdefects in silicon and their relation to point defects
Journal of Crystal Growth, 1981
It is generally agreed that microdefects. or swirl defects, in dislocation-free silicon crystals are formed by the agglomeration of point defects. Various models have been proposed, involving Si self-interstitials, vacancies and interstitial-vacancy combinations. Thermal equilibrium as well as non-equilibrium phenomena were held responsible for the origin of these point defects. In this paper all models proposed to explain the formation of swirl defects will be reviewed. It is shown that the assumption of the dominance of self-interstitials in thermal equilibrium can explain most of the experimental observations whereas all other models encounter serious difficulties in trying to describe all aspects of swirl defects.
An insight into dislocation density reduction in multicrystalline silicon
Solar Energy Materials and Solar Cells, 2016
Dislocations can severely limit the conversion efficiency of multicrystalline silicon (mc-Si) solar cells by reducing minority carrier lifetime. As cell performance becomes increasingly bulk lifetime-limited, the importance of dislocation engineering increases too. This study reviews the literature on mc-Si solar cells; it focuses on the (i) impact of dislocations on cell performance, (ii) dislocation diagnostic skills, and (iii) dislocation engineering techniques during and after crystal growth. The driving forces in dislocation density reduction are further discussed by examining the dependence of dislocation motion on temperature, intrinsic and applied stresses, and on other defects, such as vacancies and impurities.
Optical properties of dislocations in silicon crystals
Physica Status Solidi (a), 1993
New dislocation-related photoluminescence (PL) data associated with various types of extended defects in Si are considered. It is found that the D6 line in n-Si epitaxial layers is actually a doublet consisting of two lines separated by 2 meV. The D2 line strongly correlates with the presence of Frank dislocation loops in the crystals. The luminescence lines D1, D2 and the band associated with rod-like defects are quenched by a magnetic field, the lines D4, D3 are not. The magneto-quenching effect is interpreted in terms of the kinetics of carrier capture by extended defects.
Formation and nature of swirl defects in silicon
Applied Physics, 1975
Point defect agglomerates in dislocation-free silicon crystals, usually called "swirls", have been investigated by means of high-voltage electron microscopy. It was found that a single swirl defect consists of a dislocation loop or a cluster of dislocation loops. By contrast experiments it could be shown that these loops are formed by agglomeration of self-interstitial atoms. Generally the loops have a/2<110) Burgers vectors, but in specimens with high concentrations of carbon (~ 1017 cm-3) and oxygen (~ 1016 cm-3) also dislocation loops including a stacking fault were observed. In crystals grown at growth rates higher than v = 4 ram/rain no swirls are observed; lower growth rates do not markedly affect the size and shape of the dislocation loops. With decreasing impurity content (particulary of oxygen and carbon) the swirl density decreases, whereas the dislocation loop clusters become larger and more complex. A model is presented which describes the formation of swirls in terms of agglomeration of silicon self-interstitials and impurity atoms.
Recent progress in the understanding of crystallographic defects in silicon
Journal of Crystal Growth, 1993
As crystallographic defects can have a detrimental influence on the device performance, they have extensively been studied. Mainly during the last decade, however, systematical experimental studies of fundamental defect aspects have been reported. To explain the experimental observations, different theoretical models are proposed in the literature. This paper is not giving a critical overall review, but will only address some recent progress made by the authors in understanding the nucleation and the behaviour of crystallographic defects in silicon. Special attention is given to extended defect formation, oxide precipitation, critical size and morphology of precipitates, silicon yield stress, and homogeneous dislocation nucleation due to stress build-up near thin film edges. The important role played by point defects will be emphasized. The useful application of the theoretical modelling is illustrated by addressing two typical defect engineering activities, i.e gettering and lifetime engineering. A detailed understanding of defect behaviour and properties forms the basis for the defect engineering science needed to develop future advanced ULSI technologies.
Comprehensive investigation of defects in highly perfect silicon single crystals
Semiconductor Physics, Quantum Electronics and Optoelectronics
We used X-ray diffraction method of total rocking curves and nondestructive direct observation techniques (atomic force and scanning electron microscopies) to quantitatively determine the defect characteristics (radii and concentrations) for the main types of defects in Czochralski-grown silicon single crystals annealed at 750 °Ñ.
Recombination and trapping in multicrystalline silicon
IEEE Transactions on Electron Devices, 1999
Minority carrier recombination and trapping frequently coexist in multicrystalline silicon (mc-Si), with the latter effect obscuring both transient and steady-state measurements of the photoconductance. In this paper, the injection dependence of the measured lifetime is studied to gain insight into these physical mechanisms. A theoretical model for minority carrier trapping is shown to explain the anomalous dependence of the apparent lifetime with injection level and allow the evaluation of the density of trapping centers. The main causes for volume recombination in mc-Si, impurities and crystallographic defects, are separately investigated by means of cross-contamination and gettering experiments. Metallic impurities produce a dependence of the bulk minority carrier lifetime with injection level that follows the Shockley-Read-Hall recombination theory. Modeling of this dependence gives information on the fundamental electron and hole lifetimes, with the former typically being considerably smaller than the latter, in p-type silicon. Phosphorus gettering is used to remove most of the impurities and reveal the crystallographic limits on the lifetime, which can reach 600 s for 1.5 cm mc-Si. Measurements of the lifetime at very high injection levels show evidence of the Auger recombination mechanism in mc-Si. Finally, the surface recombination velocity of the interface between mc-Si and thermally grown SiO 2 is measured and found to be as low as 70 cm/s for 1.5 cm material after a forming gas anneal and 40 cm/s after an alneal. These high bulk lifetimes and excellent surface passivation prove that mc-Si can have an electronic quality similar to that of single-crystalline silicon.
Materials Science and Engineering: B, 2009
Accurate quantitative modeling of point defect and impurity aggregation during silicon crystal growth and wafer annealing requires a detailed understanding of the underlying atomic scale mechanisms involved in defect formation, diffusion, and clustering. Examples are presented that demonstrate the utility of atomic scale studies for generating a complete picture of defect aggregation in crystalline silicon. In the first example, an approach for computing the thermodynamic properties of point defect clusters at high temperature is presented that accounts for cluster configurational entropy. In the second example, a lattice kinetic Monte Carlo model is applied to the direct simulation of vacancy clustering in the presence of oxygen atoms, which are known to act as reversible vacancy traps. The simulations are able to capture complex aggregate morphologies that have been observed experimentally, in particular the cloud-like distribution of small clusters around voids, and the double-void structures frequently observed in Czochralski crystal growth.