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Hydrogen plays an important role in the passivation of interface states in silicon-based metal-oxide semiconductor technologies and passivation of surface and interface states in solar silicon. We have shown recently [Vaqueiro-Contreras et al., Phys. Status Solidi RRL 11, 1700133 (2017)] that hydrogenation of n-type silicon slices containing relatively large concentrations of carbon and oxygen impurity atoms {[Cs] ≥ 1 × 1016 cm−3 and [Oi] ≥ 1017 cm−3} can produce a family of C-O-H defects, which act as powerful recombination centres reducing the minority carrier lifetime. In this work, evidence of the silicon's lifetime deterioration after hydrogen injection from SiNx coating, which is widely used in solar cell manufacturing, has been obtained from microwave photoconductance decay measurements. We have characterised the hydrogenation induced deep level defects in n-type Czochralski-grown Si samples through a series of deep level transient spectroscopy (DLTS), minority carrier transient spectroscopy (MCTS), and high-resolution Laplace DLTS/MCTS measurements. It has been found that along with the hydrogen-related hole traps, H1 and H2, in the lower half of the gap reported by us previously, hydrogenation gives rise to two electron traps, E1 and E2, in the upper half of the gap. The activation energies for electron emission from the E1 and E2 trap levels have been determined as 0.12, and 0.14 eV, respectively. We argue that the E1/H1 and E2/H2 pairs of electron/hole traps are related to two energy levels of two complexes, each incorporating carbon, oxygen, and hydrogen atoms. Our results show that the detrimental effect of the C-O-H defects on the minority carrier lifetime in n-type Si:O + C materials can be very significant, and the carbon concentration in Czochralski-grown silicon is a key parameter in the formation of the recombination centers. [ABSTRACT FROM AUTHOR]

Research describing the instability of the spherical shape of an amorphous precipitate is presented. Observations of precipitate radius and pressure are analysed for establishing the critical value for the collapse of spheres into platelets for oxygen precipitation in silicon.

Shallow thermal donors are contained in silicon crystals doped with nitrogen, and were determined both optically and electrically.

Oxygen precipitation densities in Czochralski-grown silicon were compared with a coupled-flux model for time-dependent nucleation.

A new study aims to analyze the vacancy and self-interstitial concentration incorporated into growing silicon crystals.

Supersaturated levels of interstitial oxygen in Czochralski silicon can lead to the formation of oxide precipitates. Although beneficial from an internal gettering perspective, oxygen-related extended defects give rise to recombination which reduces minority carrier lifetime. The highest efficiency silicon solar cells are made from n-type substrates in which oxide precipitates can have a detrimental impact on cell efficiency. In order to quantify and to understand the mechanism of recombination in such materials, we correlate injection level-dependent minority carrier lifetime data measured with silicon nitride surface passivation with interstitial oxygen loss and precipitate concentration measurements in samples processed under substantially different conditions. We account for surface recombination, doping level, and precipitate morphology to present a generalised parameterisation of lifetime. The lifetime data are analysed in terms of recombination activity which is dependent on precipitate density or on the surface area of different morphologies of precipitates. Correlation of the lifetime data with interstitial oxygen loss data shows that the recombination activity is likely to be dependent on the precipitate surface area. We generalise our findings to estimate the impact of oxide precipitates with a given surface area on lifetime in both n-type and p-type silicon. [ABSTRACT FROM AUTHOR]

Experiments have been conducted to understand the behaviour of iron in silicon containing oxide precipitates and associated defects (dislocations and stacking faults), which is subjected to phosphorus diffusion gettering. Injection-dependent minority carrier lifetime measurements are analysed to provide quantitative information on the degree to which the precipitates and associated defects are decorated with iron impurities. These data are correlated with bulk iron measurements based on the photodissociation of FeB pairs. Iron in the vicinity of oxide precipitates in samples with relatively low levels of bulk iron contamination (< 5 × 1012 cm–3) can be gettered to some extent. Higher levels of bulk iron contamination (> 1.2 × 1013 cm–3) result in irreversible behaviour, suggesting iron precipitation in the vicinity of oxide precipitates. Bulk iron is preferentially gettered to the phosphorus diffused layer opposed to the oxide precipitates and associated defects. [ABSTRACT FROM AUTHOR]

Iron-related defects cause major problems in silicon for both microelectronic devices and photovoltaics. Iron contamination can occur during high temperature processing or, particularly in the case of low-cost photovoltaics, from the feedstock. In many situations, silicon is cooled too rapidly for the establishment of equilibrium, and so the bulk iron concentration exceeds the solubility value. We have investigated the relaxation of supersaturated bulk iron to the equilibrium solubility in single-crystal silicon. Bulk iron concentrations are measured by analysing the change in minority carrier lifetime that occurs when iron-boron pairs are dissociated. High-purity silicon is rubbed with iron and annealed at 750 °C for 24 h. This process creates an iron silicide phase on the rubbed surface and allows the equilibrium solubility of ∼2 × 1012 cm-3 to be established. Samples are then annealed at lower temperatures (500 to 700 °C) for a range of times. The rate of decay in iron concentration depends upon whether a silicide was formed on one side or two sides, with the kinetics in excellent agreement with iron diffusion to one or both surfaces, respectively. Even for the highest supersaturation (∼2000 times the solubility), the pre-existence of a silicide on one surface means there is insufficient driving force for nucleation of a silicide on the other surface. Relaxation experiments were also performed on contaminated samples for which the iron silicide source at the surface was removed after contamination. The iron concentration decays substantially more slowly in these specimens. The kinetics can be explained by relaxation to bulk voids. [ABSTRACT FROM AUTHOR]

Electrically detected magnetic resonance is used to identify recombination centers in a set of Czochralski-grown silicon samples processed to contain strained oxide precipitates with a wide range of densities (~1×109 cm-3 to ~7×1010 cm-3). Measurements reveal that photo-excited charge carriers recombine through Pb0 and Pb1 dangling bonds, and comparison to precipitate-free material indicates that these are present at both the sample surface and the oxide precipitates. The electronic recombination rates vary approximately linearly with precipitate density. Additional resonance lines arising from iron-boron and interstitial iron are observed and discussed. Our observations are inconsistent with bolometric heating and interpreted in terms of spin-dependent recombination. Electrically detected magnetic resonance is thus a very powerful and sensitive spectroscopic technique to selectively probe recombination centers in modern photovoltaic device materials. [ABSTRACT FROM AUTHOR]

The enhancement by carbon of vacancy-oxygen (VO) defect formation in electron irradiated silicon was investigated using many samples of various carbon contents. The effect of carbon is well described by a simple analytical model of competing trapping of self-interstitials by VO and by carbon (and by emerging carbon-related defects like CiOi and ICiOi). The trapping ratio by Cs and by VO was determined to be about 0.9, and the optical calibration coefficients for CiOi and ICiOi were deduced. In crystals containing a high concentration of Ge, germanium also acts as a self-interstitial trapping impurity and, thus, enhances VO production. The trapping efficiency of Ge is 1000 times less than that of carbon. [ABSTRACT FROM AUTHOR]

Degradation of minority carrier lifetime under illumination occurs in boron-containing Czochralski silicon of both p- and n-type. In n-Si, the recombination centre responsible for degradation is found to be identical to the fast-stage centre (FRC) known for p-Si, where it is produced at a rate proportional to the squared hole concentration, p2. Holes in n-Si are the excess minority carriers-of a relatively low concentration; hence, the time scale of FRC generation is increased by several orders of magnitude when compared to p-Si. The degradation kinetics, which is non-linear, due to dependence of p on the current concentration of FRC, is well reproduced by simulations. The injection level dependence of the lifetime shows that FRC exists in 3 charge states (- 1, 0, + 1) possessing 2 energy levels. Comparison of n-Si samples of various electron concentrations shows that FRC emerges by the reconstruction of a latent BsO2 complex of a substitutional boron and an oxygen dimer (while the major recombination centre in p-Si denoted SRC was previously found to emerge by reconstruction of BiO2 defect involving an interstitial boron atom). A model of the BsO2 reconfiguration into FRC through an intermediate state accounts for the rate constant dependence on p, which is reduced to a p2 proportionality, under certain conditions. [ABSTRACT FROM AUTHOR]

Transient and quasi-steady-state photoconductance methods were used to measure minority carrier lifetime in ∼10 ࡎ cm p-type Czochralski silicon processed in very clean conditions to contain oxide precipitates. The nucleation and growth times for precipitation were varied to produce 35 samples, which were then characterised by chemical etching and transmission electron microscopy to determine the density and morphology of the precipitates. The effects of other known recombination mechanisms (band-to-band, Coulomb-enhanced Auger, iron-related, and boron-oxygen related) were factored out to isolate the lifetime component associated with the precipitates as accurately as possible. In the samples processed to contain mainly unstrained precipitates, it was shown that the lifetime component due to the precipitates could be extremely high (up to ∼4.5 ms). Recombination at unstrained precipitates is weak and it is estimated that the capture coefficient lies between 3 × 10-8 cm3 s-1 and 1.3 × 10-7 cm3 s-1 at an injection level corresponding to half the doping level. Strained precipitates act as strong recombination centres with a capture coefficient of ∼1 × 10-6 cm3 s-1 at the same level of injection. For the samples investigated, the effective capture coefficient is increased by a factor of ∼3 to 4 when other extended defects (such as dislocations and stacking faults) accompany the strained precipitates. The shape of the injection level dependence of lifetime was similar for all the specimens studied, with the magnitude of the lifetime being dependent on the precipitate density and strain state but approximately independent of precipitate size. [ABSTRACT FROM AUTHOR]

Oxygen diffusion in silicon is known to be affected by high concentrations of impurities, although the mechanism underpinning this is poorly understood. We have studied oxygen transport in Czochralski silicon by analyzing data on the locking of dislocations by oxygen as a function of time and temperature. In this paper, we present new data from crystals grown to contain high levels of germanium and arsenic. We analyze these new data, together with our previous data for silicon with a high boron concentration, to further the understanding of the mechanism by which high impurity concentrations affect oxygen transport at temperatures at which the oxygen dimer dominates transport (up to 550 °C). Our results show that a high level of boron doping (∼3 × 1018cm-3) enhances the effective diffusivity of oxygen by a factor of ∼8 to ∼25 relative to low doped material with the same oxygen concentration. High levels of germanium doping (∼8 × 1019cm-3) and arsenic doping (∼2 × 1019cm-3) can both have a slight retardation effect on oxygen transport. The magnitude of the reduction measured is less than a factor of ∼4 in the heavily germanium doped specimens and less than a factor of ∼5 in the heavily arsenic doped specimens, and in most cases is significantly less than this. Germanium doping introduces considerable strain into the silicon lattice without affecting the Fermi level position, so data from these samples show that lattice strain affects oxygen dimer transport. The arsenic and boron doping levels in the materials studied give rise to lattice strain with a smaller magnitude and opposite sign to that in the germanium doped samples. It is therefore suggested that the Fermi level position also affects the transport of oxygen dimers. [ABSTRACT FROM AUTHOR]

Reduction in electron lifetime induced by excess electrons is a key effect in degradation of solar cells based on boron-doped and oxygen-containing silicon. Although boron related, degradation is controlled by the concentration of holes and not by the boron concentration. This recent finding is the basis for a new degradation model in which the degradation starts from a latent complex BiO2 of an interstitial boron atom and an oxygen dimer. Electron-induced reconstruction of this defect results in a production of recombination centers. This model provides a detailed explanation of the basic features of the degradation, and of subsequent recovery by annealing in the dark. [ABSTRACT FROM AUTHOR]

The results of dislocation unlocking experiments are reported. The stress required to unpin a dislocation from nitrogen impurities in nitrogen-doped float-zone silicon (NFZ-Si) and from oxygen impurities in Czochralski silicon (Cz-Si) is measured, as a function of the unlocking duration. It is found that unlocking stress drops with increasing unlocking time in all materials tested. Analysis of these results indicates that dislocation locking by nitrogen in NFZ-Si is by an atomic species, with a similar locking strength per atom to that previously deduced for oxygen atoms in Cz-Si. Other experiments measure dislocation unlocking stress at 550 °C in NFZ-Si annealed at 500–1050 °C. The results allow an effective diffusivity of nitrogen in silicon at 500–750 °C to be inferred, with an activation energy of 3.24 eV and a diffusivity prefactor of approximately 200 000 cm2 s-1. This effective diffusivity is consistent with previous measurements made at higher temperatures using secondary ion mass spectrometry. When the results are analyzed in terms of a monomer-dimer dissociative mechanism, a nitrogen monomer diffusivity with an activation energy in the range of 1.1–1.4 eV is inferred. The data also show that the saturation dislocation unlocking stress measured at 550 °C in NFZ-Si is dependent on the anneal temperature, peaking at 600–700 °C and falling toward zero at 1000 °C. [ABSTRACT FROM AUTHOR]

The locking of dislocations by oxygen has been investigated experimentally in Czochralski silicon (Cz-Si) with different concentrations of shallow dopants. Specimens containing well-defined arrays of dislocation half-loops were subjected to isothermal anneals in the 350–550 °C temperature range, and the stress required to bring about dislocation motion at 550 °C was then measured. This dislocation unlocking stress was found to increase with annealing time due to oxygen diffusion to the dislocation core. The dislocation unlocking stress was measured in n-type Cz-Si with a high antimony doping level (∼3.4×1018 cm-3) and p-type Cz-Si with a low boron doping level (∼1.3×1015 cm-3). An analysis of the data taking the different oxygen concentrations into account showed that the rate of increase in dislocation unlocking stress was unaffected by the high level of antimony doping. This indicates that a high antimony doping level has no significant effect on oxygen transport for the conditions used in this experiment. However, in p-type Cz-Si with a high boron doping level (∼5.4×1018 cm-3), the dislocation unlocking stress was found to rise at a much faster rate than in Cz-Si with a low boron doping level or high antimony doping level. This enhancement in dislocation locking was by a factor of approximately 60 at 400 °C. By performing a numerical simulation to solve the diffusion equation for oxygen transport to a dislocation, the effective diffusivity of oxygen was deduced from the dislocation unlocking data to be 2.7×10-6 exp(-1.4 eV/kT) cm2 s-1 in the highly boron doped Cz-Si. In the temperature range studied, the effective diffusion coefficient in the highly boron doped Cz-Si was found to be approximately 44 times higher than expected in low boron doped Cz-Si with an identical oxygen concentration. [ABSTRACT FROM AUTHOR]