Capture Cross Section Ratio Research Articles

Modification on electrical characteristics of interface states by using nitrogen and phosphorus co-doped polysilicon in tunnel oxide passivation contact silicon solar cells

The influence on electrical characteristics of interface states by using nitrogen (N) and phosphorus (P) co-doped polysilicon (poly-Si) in tunnel oxide passivation contact silicon solar cells has been investigated. We find that the introduction of N co-doping in P heavily doped poly-Si decreases its own work function; thus, the built-in potential of the poly-Si (n+)/tunnel SiOx/c-Si (p) junction is notably enhanced. The electrical characteristics of interface states at tunnel SiOx/c-Si in the junction have been investigated by current/capacitance–voltage deconvolution. The measured results suggest that the interface state density is reduced, and the corresponding capture cross section ratio σe/σh is increased by three orders of magnitude in the junction with N co-doped poly-Si. The obtained results not only reveal the underlying mechanism of the enhanced contact passivation effect by introducing N co-doped poly-Si but also give an enlightening idea for the design of passivation contact structure in crystalline silicon solar cells.

Assessing the stability of p+ and n+ polysilicon passivating contacts with various capping layers on p-type wafers

Polysilicon (poly-Si)-on-oxide passivating contact structures (POLO/TOPCon) enable high-efficiency solar cells as they simultaneously provide a very high level of surface passivation and a high conductance for either electrons or holes. The ease of incorporation with existing manufacturing lines and their tolerance for high-temperature processing has increased the wide acceptance of this structure in the PV industry. In this report, we explore the effects of short high-temperature annealing required for effective hydrogenation and formation of ohmic screen-printed contacts across a wide temperature range (636 °C–846 °C) on the stability of passivating contact structures. We study this on p-type c-Si substrates with phosphorus-doped (n-type) or boron-doped (p-type) polysilicon contacts capped with either an AlOx or SiNx coating. Our experimental results show that irrespective of the poly-Si doping type, AlOx-capped samples suffer a loss in surface passivation across the investigated temperature range, while SiNx-capped samples show an improvement at lower annealing temperatures. Above 744 °C, severely ruptured blisters occur for the samples coated with a SiNx layer, leading to lift-off of the poly layer in extreme cases, and in all cases, significant surface passivation losses, up to 99%. A study of the long-term stability of these fired samples under 1-sun illumination @ 140 °C shows that they suffer from both bulk and surface-like instabilities. Two degradation cycles were observed: the first, a boron-oxygen light-induced degradation (BO-LID) observed after 5 min, with capture cross-section ratios of 15.8–19.2, and a slower secondary degradation, similar to light and elevated temperature-induced degradation (LeTID), with maximum degradation reached after ∼ 14 days. The presence of a silicon nitride layer does not appear to influence the kinetics of post-degradation recovery. Our results suggest that the effect of firing may be influenced by the polarity of the bulk c-Si or perhaps the chemistry of the SiNx film and highlight that passivating contact structures based on p-type c-Si may offer better long-term stability than those based on n-type c-Si.

Investigation of Light-Induced Degradation in B-Doped Mono-Like Silicon PERC Cells by a Cycling Test With Light Soaking and Dark Annealing

We investigated light-induced degradation (LID) of passivated emitter and rear contact cells fabricated from B-doped cast-grown mono-like Si by conducting a cycling test comprising light soaking (illumination intensity of 1 sun at 95 °C) and dark annealing (at 175 °C for 30 min). Degradation and regeneration were observed in both the first light soaking (LS1) and subsequent light soaking after dark annealing (LS2 and LS3), but the extent and timescale were significantly different. The normalized defect density (NDD) during light soaking was analyzed by fitting based on first-order consecutive reaction models. Systematic residuals between the NDD and the three-state consecutive reaction model were observed in the early and regeneration regions during LS1. We discussed the scenarios that could explain the cause of these residuals, and the values of the reaction rate constants and capture cross-section ratio suggested that two types of LIDs occurred simultaneously in LS1. We concluded that one of the two types of LIDs was light- and elevated-temperature-induced degradation, but we could not identify the other LID with a larger extent and timescale.

Effect of Doping, Photodoping, and Bandgap Variation on the Performance of Perovskite Solar Cells

AbstractMost traditional semiconductor materials are based on the control of doping densities to create junctions and thereby functional and efficient electronic and optoelectronic devices. The technology development for halide perovskites had initially only rarely made use of the concept of electronic doping of the perovskite layer and instead employed a variety of different contact materials to create functionality. Only recently, intentional or unintentional doping of the perovskite layer is more frequently invoked as an important factor explaining differences in photovoltaic or optoelectronic performance in certain devices. Here, numerical simulations are used to study the influence of doping and photodoping on photoluminescence quantum yield and other device relevant metrics. It is found that doping can improve the photoluminescence quantum yield by making radiative recombination faster. This effect can benefit, or harm, photovoltaic performance given that the improvement of photoluminescence quantum efficiency and open‐circuit voltage is accompanied by a reduction of the diffusion length. This reduction will eventually lead to inefficient carrier collection at high doping densities. The photovoltaic performance may improve at an optimum doping density which depends on a range of factors such as the mobilities of the different layers and the ratio of the charge carrier capture cross sections.

Bulk defect characterization in metalized solar cells using temperature-dependent Suns-Voc measurements

Extracting the parameters, energy level and electron-to-hole capture cross-section ratio, of efficiency-limiting bulk defects in silicon solar cells is a critical step in identifying those defects and potentially eliminating their impact. Typically, this is achieved on specially prepared test structures. However, in some cases, this is not possible, especially in mass production lines when only completed solar cells are available. In this study, a method that is based on temperature-dependent Suns-V oc measurements is introduced to extract the defect parameters in metalized solar cells. The method is validated by comparing the parameters of the boron-oxygen-related defect extracted from cells and those extracted from wafers using the commonly used temperature- and injection-dependent lifetime spectroscopy. It is shown that this method has the benefit of a more accurate lifetime at low injection levels compared with photoconductance-based lifetime measurement since it is not impacted by minority carrier traps. The proposed technique is then applied to determine the parameters of the defect causing light-induced degradation in gallium-doped silicon solar cells. We determined an energy level, with respect to the intrinsic level, of −0.26 ± 0.04 eV and a capture cross-section ratio of 34 ± 2 for this defect. Finally, a sensitivity analysis is performed by considering the system’s limited measurement temperature range. The findings demonstrate the potential of the temperature-dependent Suns-V oc method as a fast and easy-to-apply method for defect characterization in metalized cells. • Parameters of bulk defects in cells can be extracted using Sun-V oc (T) method. • The method is validated by extracting the parameters of BO-related defects. • The parameters of LID-related defects in Ga-doped cells are extracted with the method. • Sensitivity analysis is performed to assess the limitations of the method.

Measurements of the Bi210g to Bi210m activation ratio for the Bi209 ( n ,γ) reaction with thermal and epithermal neutrons at the Soreq IRR1 reactor

Irradiations of bismuth samples with thermal and epithermal neutrons have been performed for a comparison of activation to the $^{210g}\mathrm{Bi}$ ground state and to the $^{210m}\mathrm{Bi}$ metastable state. The bismuth irradiations were conducted at the Soreq IRR1 research reactor at a near-core location with integrated neutron flux of approximately $2\ifmmode\times\else\texttimes\fi{}{10}^{18}\mathrm{neutrons}/\mathrm{c}{\mathrm{m}}^{2}$ and a gold cadmium ratio of 3.1. Two nearly identical bismuth samples were irradiated, one without and one with a cadmium shield, to enable a comparison between thermal and epithermal neutron capture cross sections. Subsequent gamma spectrometry indicates nearly equal levels of activation to the ground and to the metastable states of $^{210}\mathrm{Bi}$, both with thermal and epithermal neutrons. Absolute thermal cross sections and resonant integrals were deduced by including previously reported bismuth activation measurements performed conjointly with gold foil activation for normalization. A comparison of the present results with existing data is presented. It is argued that the bismuth resonances lie in the neutron energy range relevant for stellar temperatures, and therefore the neutron capture cross section ratio $({\ensuremath{\sigma}}_{g}/{\ensuremath{\sigma}}_{m})$ measured for the epithermal neutrons is relevant also for stellar $^{210}\mathrm{Bi}$ production. This is of importance since bismuth lies at the end of the chain for the s\penalty1000-\hskip0ptprocess reaction for nucleosynthesis in stars. Precise knowledge of bismuth activation to the $^{210m}\mathrm{Bi}$ metastable state is also vital for the planning of GEN-IV reactors given the 3-million-yr half-life of $^{210m}\mathrm{Bi}$.

Defect concentration and Δn change in light- and elevated temperature-induced degradation

The wide variety of silicon materials used by various groups to investigate LeTID make it difficult to directly compare the defect concentrations (N t) using the typical normalised defect density (NDD) metric. Here, we propose a new formulation for a relative defect concentration (β) as a correction for NDD that allows flexibility to perform lifetime analysis at arbitrary injection levels (Δn), away from the required ratio between Δn and the background doping density (N dop) for NDD of Δn/N dop = 0.1. As such, β allows for a meaningful comparison of the maximum degradation extent between different samples in different studies and also gives a more accurate representative value to estimate the defect concentration. It also allows an extraction at the cross-over point in the undesirable presence of iron or flexibility to reduce the impact of modulation in surface passivation. Although the accurate determination of β at a given Δn requires knowledge of the capture cross-section ratio (k), the injection-independent property of the β formulation allows a self-consistent determination of k. Experimental verification is also demonstrated for boron-oxygen related defects and LeTID defects, yielding k-values of 10.6 ± 3.2 and 30.7 ± 4.0, respectively, which are within the ranges reported in the literature. With this, when extracting the defect density at different Δn ranging between 1014 cm−3 to 1015 cm−3 with N dop = 9.1 × 1015 cm−3, the error is less than 12% using β, allowing for a greatly improved understanding of the defect concentration in a material.

Investigation on the light and elevated temperature induced degradation of gallium-doped Cz-Si

In this study, we performed light and elevated temperature induced degradation (LeTID) experiments in gallium-doped Czochralski silicon (Cz-Si) wafers and investigated the impact of temperature on reaction kinetics. The degradation was found to have a fast and a slow process, and their reaction rates were extracted by using an exponential function. We further determined the activation energies of each degradation as well as the regeneration according to Arrhenius plots. Moreover, we found that the capture cross-section ratio of the generated defect remained in the range of 27 < k < 35 throughout the degradation. Based on these findings, we suggested that both fast and slow degradation might be attributed to the generation of a same recombination-active defect from different precursors, and consequently have different reaction rates.

Thermophysical Characterization of Efficiency Droop in GaN-Based Light-Emitting Diodes.

An efficiency droop in GaN-based light-emitting diodes (LED) was characterized by examining its general thermophysical parameters. An effective suppression of emission degradation afforded by the introduction of InGaN/GaN heterobarrier structures in the active region was attributable to an increase in the capture cross-section ratios. The Debye temperatures and the electron–phonon interaction coupling coefficients were obtained from temperature-dependent current-voltage measurements of InGaN/GaN multiple-quantum-well LEDs over a temperature range from 20 to 300 K. It was found that the Debye temperature of the LEDs was modulated by the InN molar fraction in the heterobarriers. As far as the phonons involved in the electron–phonon scattering process are concerned, the average number of phonons decreases with the Debye temperature, and the electron–phonon interaction coupling coefficients phenomenologically reflect the nonradiative transition rates. We can use the characteristic ratio of the Debye temperature to the coupling coefficient (DCR) to assess the efficiency droop phenomenon. Our investigation showed that DCR is correlated to quantum efficiency (QE). The light emission results exhibited the high and low QEs to be represented by the high and low DCRs associated with low and high injection currents, respectively. The DCR can be envisioned as a thermophysical marker of LED performance, not only for efficiency droop characterization but also for heterodevice structure optimization.

Impurity photovoltaic and split spectrum for efficiency gain in Cu2ZnSnS4 solar cells

Cu2ZnSnS4 (CZTS) solar cells are potential terawatt scale photovoltaic materials due to optimal bandgap and cost-effective synthesis process. However, it shows low efficiency. We have simulated two avenues of efficiency enhancement in Cu2ZnSnS4 solar cells, viz., impurity photovoltaic, and Split-spectrum strategy. An impurity energy level 0.4 eV above valence band with high electron/hole capture cross-section ratio shows an optimum sub-bandgap absorption of wavelengths up to 1127 nm leading to a short-circuit current (JSC), an observation of beyond Shockley-Queisser (SQ) limit. Secondly, the bandgap tunability of Cu2ZnSnS4 is utilized to design a point focusing spectral splitting system, where we numerically showed an enhancement in efficiency. The spectrum is split into three regions, which are focused on bandgap-matched solar cells to absorb a wider spectrum, and reduced thermalization, transmission losses. A conservative calculation using point-focused spectral splitting shows an efficiency up to 19.4 %, a significant improvement compared to the best-reported efficiency of 12.6 % in the literature.

Investigation of silicon surface passivation by sputtered amorphous silicon and thermally evaporated molybdenum oxide films using temperature- and injection-dependent lifetime spectroscopy

Crystalline silicon (c-Si) surface passivation has been investigated by sputtered hydrogenated intrinsic amorphous silicon (S-i-a-Si:H) and thermally evaporated molybdenum oxide (MoOx) thin films. The temperature- and injection-dependent lifetime spectroscopy technique has been adopted for analyzing the passivation quality of the c-Si surface, using parameters such as the minority carrier effective lifetime (τeff), the activation energy of surface/interface defect states (ΔE), and the electron to hole carrier capture cross-section ratio (k) at the interface. With S-i-a-Si:H films, a τeff of ∼70 µs and ΔE of ∼51 meV have been observed in comparison to a τeff of ∼110 µs and ΔE of ∼109 meV from the MoOx films. These entirely different parameters are an indication of the relatively strong carrier recombination with dense interface/surface states from the S-i-a-Si:H passivation layers. The S-i-a-Si:H layers are unable to minimize the c-Si surface trap states with the chemical passivation for reducing carrier recombination due to the generation of additional surface defect states by the sputtering damage. However, the MoOx layers show better c-Si surface passivation due to the reduction of majority carriers by the carrier inversion (field-effect passivation) and chemical passivation. This effect is clearly reflected with the opposite trend in the carrier capture analysis from S-i-a-Si:H and MoOx layers.

Comparison of three IBSCs in terms of photo-filling, capture cross section of carriers, the concentration of IB states and overlapping of absorption coefficients in the wide range of band gaps including GaAs

Intermediate-band solar cells, IBSCs, with single IB provide better utilization of the solar spectrum than single junction solar cells. In this study, Model−B IBSC was proposed, investigated and compared with previously used two models named here as Model−A and Model−C respectively. Detailed Balance Model was applied to satisfy Current Balance Equations with the optimum photo filling of IB states in Model−B. Optimum design parameters were obtained using 104 cm−1 of band-to-band absorption coefficient, α, in the wide range of band gap materials, overlapping absorption, photo filling, f, of IB states, capture cross-section ratio of carriers, concentration of IB states, and IB layer thickness, w, under 1–46,000 sun concentration, X. Maximum limiting efficiency value of 63.2% has been obtained with 1.95 eV of band gap, for fαw≥5 and 46,000X, under non-overlapping absorption. The peak efficiency of Model−B was 16% over the Model−A and 8% over the Model−C, for equal capture cross sections under large overlapping. The peak efficiency of Model−B was 35% over Model−A, at large non-equal capture cross-sections and large overlapping. Results predicted that the materials in the wide range of band gaps could be good candidates for fabricating IBSCs using Model−B with an efficiency of 50% or above at lower sun concentration, 10,000X, even under large overlapping.

Extracting bulk defect parameters in silicon wafers using machine learning models

The performance of high-efficiency silicon solar cells is limited by the presence of bulk defects. Identification of these defects has the potential to improve cell performance and reliability. The impact of bulk defects on minority carrier lifetime is commonly measured using temperature- and injection-dependent lifetime spectroscopy and the defect parameters, such as its energy level and capture cross-section ratio, are usually extracted by fitting the Shockley-Read-Hall equation. We propose an alternative extraction approach by using machine learning trained on more than a million simulated lifetime curves, achieving coefficient of determinations between the true and predicted values of the defect parameters above 99%. In particular, random forest regressors, show that defect energy levels can be predicted with a high precision of ±0.02 eV, 87% of the time. The traditional approach of fitting to the Shockley-Read-Hall equation usually yields two sets of defect parameters, one in each half bandgap. The machine learning model is trained to predict the half bandgap location of the energy level, and successfully overcome the traditional approach’s limitation. The proposed approach is validated using experimental measurements, where the machine learning predicts defect energy level and capture cross-section ratio within the uncertainty range of the traditional fitting method. The successful application of machine learning in the context of bulk defect parameter extraction paves the way to more complex data-driven physical models which have the potential to overcome the limitation of traditional approaches and can be applied to other materials such as perovskite and thin film.

Evolution of LeTID defects in industrial multi-crystalline silicon wafers under laser illumination - Dependency of wafer position in brick and temperature

In the past few years, a hot topic in both research and industrialization of p-type multi-crystalline silicon (mc-Si) solar cells is to investigate the mechanism, measurement and mitigation of the light- and elevated temperature-induced degradation (LeTID), which has been found to be a bulk-sensitive degradation behavior and is dependent on the degradation condition. In this paper, we study the influence of silicon bulk property on LeTID from five representative positions along a relative low resistivity (0.82–1.33 Ω cm) p-type mc-Si brick. The evolution of degradation and regeneration under different laser illumination conditions are investigated. Identical defect capture cross section ratio k values of ~35 at mid-gap along the brick height are found. For the first time, the activation energy for degradation (Ea,deg) and regeneration (Ea,reg) along the brick are studied, which shows Ea,deg = Ea,reg and a tendency of larger values towards the brick bottom. These results indicate that the LeTID in the whole brick might be induced by a single defect and thus mitigated in a single manner. Besides, a laser illumination of 45 kW/m2 at 142 °C for 100 s is able to induce over 90% degradation for all wafers, which could be used as a universal and fast LeTID test condition.

The Role of Dark Annealing in Light and Elevated Temperature Induced Degradation in p-Type Mono-Like Silicon

We have studied lifetime instabilities in p-type boron-doped mono-like silicon during light soaking (LS) and dark annealing (DA) at different temperatures, and their behavior upon LS/DA cycling at various degradation and regeneration stages. Despite having similar capture cross section ratios, it is found that the defects responsible for the degradation under illumination and in the dark could stem from two separate reactions, with hydrogen being the common precursor. A model for light and elevated temperature induced degradation (LeTID) is presented based on our experimental findings. It is proposed that hydrogen atoms originally bound in the silicon nitride layer are released into the silicon bulk above a certain firing temperature, which then interact with some other species in the silicon bulk under illumination, causing the LeTID degradation. During the cooling ramp of the firing process or extended DA, hydrogen in the silicon bulk starts to effuse into the ambient, reducing the amount of hydrogen remaining in the silicon bulk, and correspondingly affecting their LeTID behavior. The proposed model provides new insights to help understand complex LeTID behaviors reported in the literature, including its dependence on the firing profile, sample thickness, dopant type, and DA pretreatment.

Heterogeneous effects in simulating a fast nuclear reactor on the BFS test facility

Simulating fast neutron reactor cores for comparing experimental and calculated data on the reactor neutronics characteristics is performed using zero power test stands. The BFS test facilities in operation in Russia (Obninsk) are discussed in the present paper. The geometrical arrangement of materials in the cores of the simulated reactors (fuel pins, fuel assemblies, coolant geometry) differs from the simulation assembly on the BFS. This can cause differences between the experimental results obtained at the BFS and theoretical calculations even in the case when homogenized concentrations of all materials of the reactor are thoroughly observed. The resulting differences in neutronics parameters due to the geometry of arrangement of materials with the same homogeneous concentrations are referred to as the heterogeneous effect. Heterogeneous effects tend to increase with increasing reactor power and its size, mainly due to changes in the neutron spectra. Calculations of a number of functional values were carried out for assessing the heterogeneous effects for different spatial arrangements of the reactor materials. The calculations were performed for the following cases: a) heterogeneous distribution of materials in accordance with the design of a fast reactor; b) heterogeneous arrangement of materials in accordance with the capabilities and design features of the BFS test facility; c) homogeneous representation of materials in the reactor core and breeding blankets. The configuration of materials in accordance with the design data for fast reactors of the BN-1200 type was accepted as the basic calculation option, relative to which the effect called the heterogeneous shift of the functional value (HSF) was calculated. The effect of neutron leakage on the HSF obtained as the result of calculations using different boundary conditions was estimated. All calculations were carried out for the same homogeneous concentrations of all materials for all the above three configurations. Calculations were carried out as well for the case when plutonium metal fuel was used in the BFS. The values of the following functionals were calculated for different cases of arrangement of materials: the effective multiplication factor (reactivity), the sodium void reactivity effect, the average energy of fission-inducing neutrons, and the ratios of radioactive capture cross-sections to fission cross-sections for 239Pu. The calculations were performed using the Serpent 2.1.30 (VTT, Finland) Monte Carlo software package for neutronics simulations and ENDF/B-VII.0 and JEFF-3.1.1 evaluated nuclear data libraries. The effects of various options of material arrangement on the values of keff were found to be the greatest (about 1.6%) for the case when fissile material in the form of dioxide is replaced with metal fissile material. Homogenization of the composition reduces the keff value by about 0.4%. The average energy of fission-inducing neutrons depends to a significant extent on the leakage of neutrons and the presence of sodium (the average energy of neutrons increases and reaches in the presence of sodium about 100 keV, that is, it increases by about 11–13%). Replacing fissile material metal with its dioxide in the BFS test facility (while maintaining homogeneous concentrations, including that of oxygen) allows reducing the average energy of fission-inducing neutrons by about 60 keV. The highest values of HSF, reaching 65%, are observed when calculation of sodium void reactivity effect is performed with materials distributed homogeneously; however, HSF is equal to 1.5% when calculation of the reactor mock-up assembled on the BFS is performed. In the absence of neutron leakage (infinitely extended medium), the sodium void reactivity effect becomes positive and the HSF is equal to 4–7%. The heterogeneous effect of α for 239Pu noticeably (6–8%) depends only on the replacement of metallic plutonium with its dioxide (maintaining, of course, the homogeneous concentrations).

Lifetime spectroscopy with high spatial resolution based on temperature- and injection dependent photoluminescence imaging

In this paper we present a method for performing temperature- and injection dependent lifetime spectroscopy (TIDLS) with high spatial resolution based on steady state photoluminescence (PL) images taken at a range of excitation intensities and temperatures. The PL lifetime images are calibrated based on temperature dependent photoconductance measurements, thus requiring a minimum of assumptions regarding the temperature dependency of the luminescence signal and detection system. PL image acquisition at varying conditions and subsequent data analysis is automated, allowing for investigations of different samples without the need for excessive operator time. We demonstrate the method by presenting lifetime data and TIDLS analysis from commercial HPMC-Si samples, highlighting the local differences in the recombination properties for high lifetime in-grain areas and lower lifetime areas dominated by dislocation clusters. These regions have been investigated for two etched and passivated neighboring wafers, one in the as-cut state and one where the bulk lifetime had been improved through key solar cell process steps. For the as-cut wafer we find two dominant defects in the low lifetime area, one of which is identified as FeB pairs, with Et = 0.90 ± 0.01 (above the valence band) and k = 0.4 ± 0.1. In the in-grain region of this wafer we also observe two dominating defects, one with an energy level of either 0.28 ± 0.01 eV or 0.74 ± 0.01 eV above the valence band and a k value of 25 ± 1. The other defect is shallow, within ~0.27 eV of the band edge, and could not be further identified with the chosen temperature range. For the wafer that had passed through solar cell processing, we find a clear, overall improvement in the lifetime and a change in the type of dominating defects: We observe that a single, deep defect with 0.35 eV < Et < 0.7 eV and a capture cross section ratio k = 10 ± 1 can fully describe the observed lifetime data in the in-grain area after solar cell processing, whereas two defects are needed to describe the behavior of the lower lifetime regions. One of these defects is also a deep defect with 0.34 eV < Et < 0.69 eV but with a higher k of 25 ± 2, and is thus similar to one of the defects observed in the in-grain region of the as-cut wafer. The other is a shallow defect with Et within 0.21 eV of the band edge. Finally, we show how the method can be used to show interesting new properties of the lifetime maps, including maps of the temperature coefficient of the lifetime, maps of the injection dependence of the lifetime and maps at a constant injection level.

Preliminary results on the 233U capture cross section and alpha ratio measured at n_TOF (CERN) with the fission tagging technique

233U is of key importance among the fissile nuclei in the Th-U fuel cycle. A particularity of 233U is its small neutron capture cross-section, which is on average about one order of magnitude lower than the fission cross-section. The accuracy in the measurement of the 233U capture cross-section depends crucially on an efficient capture-fission discrimination, thus a combined set-up of fission and γ-detectors is needed. A measurement of the 233U capture cross-section and capture-to-fission ratio was performed at the CERN n_TOF facility. The Total Absorption Calorimeter (TAC) of n_TOF was employed as γ-detector coupled with a novel compact ionization chamber as fission detector. A brief description of the experimental set-up will be given, and essential parts of the analysis procedure as well as the preliminary response of the set-up to capture are presented and discussed.

Hydrogen induced degradation: A possible mechanism for light- and elevated temperature- induced degradation in n-type silicon

In this work, we demonstrate a form of minority carrier degradation on n-type Cz silicon that affects both the bulk and surface related lifetimes. We identify three key behaviors of the degradation mechanism; 1) a firing dependence for the extent of degradation, 2) the appearance of bulk degradation when wafers are fired in the presence of a diffused emitter and 3) a firing related apparent surface degradation when wafers are fired in the absence of an emitter. We further report a defect capture cross-section ratio of σn/σp = 0.028 ± 0.003 for the defect in n-type. Utilizing our understanding of light and elevated temperature induced degradation (LeTID) in p-type silicon, we demonstrate that the degradation behaviors in both n-type and p-type silicon are closely correlated. In light of numerous reports on the involvement of hydrogen, the potential role of a hydrogen-induced degradation mechanism is discussed in both p- and n-type silicon, particularly in relation to the diffusion of hydrogen and influence of hydrogen-dopant interactions.

Defect Parameters Contour Mapping: A Powerful Tool for Lifetime Spectroscopy Data Analysis

Temperature‐ and injection‐dependent lifetime spectroscopy (TIDLS) is extensively used for the characterization of defects in silicon material for photovoltaic applications. By coupling TIDLS measurements with Shockley–Read–Hall recombination models, the most important defects’ parameters can be assessed including the defect energy level Et and the capture cross section ratio k. However, while proving extremely helpful in a variety of studies aiming at the characterization of contaminated silicon, a generalized approach for the analysis of industrially‐relevant material has not yet emerged. In this contribution, we examine in detail the recently introduced defect parameters contour mapping (DPCM) methodology for TIDLS data analysis as a tool for direct visualization of possible lifetime limiting defects. Herein, we showcase the DPCM method's potential by applying it to two representative case studies selected from literature and we demonstrate that, even when data are scarce, invaluable information is obtained in an easy and intuitive way without any a priori assumption needed. We then apply the DPCM method to simulated TIDLS data to evaluate the general characteristics of its response and the optimal conditions for its application. This analysis proves that the temperature dependence of lifetime is the most critical information required toward a really univocal identification of metal impurities.