Search

Understanding and characterizing very low-energy (∼ eV) background sources is a must in rare-event searches. Oscura, an experiment aiming to probe electron recoils from sub-GeV dark matter using a 10 kg skipper-CCD detector, has recently fabricated its first two batches of sensors. In this work, we present the characterization of defects/contaminants identified in the buried-channel region of these newly fabricated skipper-CCDs. These defects/contaminants produce deferred charge from trap emission in the images next to particle tracks, which can be spatially resolved due to the sub-electron resolution achieved with these sensors. Using the trap-pumping technique, we measured the energy and cross section associated with these traps in three Oscura prototype sensors from different fabrication batches which underwent different gettering methods during fabrication. Results suggest that the type of defects/contaminants is more closely linked to the fabrication batch rather than to the gettering method used. The exposure-dependent single-electron rate (SER) of one of these sensors was measured ∼ 100 m underground, yielding (1.8 ± 0.3) × 10 − 3 e − /pix/day at 131 K. The impact of the identified traps on the measured exposure-dependent SER is evaluated via a Monte Carlo simulation. Results suggest that the exposure-dependent SER of Oscura prototype sensors would be lower in lower background environments as expected. [ABSTRACT FROM AUTHOR]

Metallic impurities in the silicon wafer bulk are one of the major efficiency-limiting factors in silicon solar cells. Gettering can be used to significantly lower the bulk metal concentrations. Aluminum oxide thin films from plasma-enhanced atomic layer deposition (PE-ALD) have been reported to getter iron from silicon wafers. However, its gettering mechanism and kinetics remain unclear. In this study, by experimentally monitoring the kinetics of iron reduction in the silicon wafer bulk, aluminum oxide gettering of iron is shown to be caused by a segregation mechanism. Fitting the experimental iron reduction kinetics by the simulation of a segregation gettering process based on various diffusion scenarios suggests that the gettering kinetics is limited by both the diffusivities of iron in the silicon wafer bulk and in the aluminum oxide film. The activation energy of the segregation gettering process (negative meaning exothermic reaction) is estimated to be −0.47 ± 0.16 eV for the investigated as-deposited PE-ALD aluminum oxide film at 550–900 °C, and −0.35 ± 0.06 eV at 400–900 °C for the same film after a 400 °C forming gas anneal (FGA), i.e., after activating the passivation effect of the film. Capacitance–voltage measurements of the films indicate a higher surface defect density in the as-deposited films as compared to the FGA-activated films, which suggests a possible correlation between the surface defect density and gettering. [ABSTRACT FROM AUTHOR]

The paper studies the gettering properties of nickel clusters in the silicon lattice. The gettering properties of nickel clusters were studied in various states, i.e., in original (reference) samples, as well as in samples with additionally doped interstitial and lattice site impurity atoms of sulfur and manganese. The electrophysical and photoelectric parameters were studied using modern instrumentation: INFRAM-I-type infrared microscope, IKS-21 and scanning electron microscope SEM (Oxford Instruments ZEISS EVOMA10), IKS-21. A new technology has also been proposed that makes it possible to getter harmful impurities; it is recommended for widespread use in the electronics industry and scientific research institutes for the production of materials with stable parameters and the development of fundamentally new devices. [ABSTRACT FROM AUTHOR]

Titanium zirconium vanadium (TiZrV) is a widely used non-evaporable getter (NEG) material with the characteristics of a low activation temperature and a large gas absorption capacity. At present, the research on TiZrV getters mainly focuses on the thin-film state, with little research on the bulk state. In this paper, a TiZrV getter was optimized by adding Al, and the phase structure, activation properties, and gettering performance were studied. With the addition of Al, the α-Zr phase and Ti2Zr phase changed into the Ti-Zr phase and Al-Zr, Al-Ti phase. The newly generated phase promoted the diffusion of hydrogen and oxygen atoms. The activation temperature decreased significantly, as shown in the in situ XPS results. The H2 and CO gettering performance of TiZrVAl samples was promoted to 2073 cm3·s−1 and 1912.8 cm3·s−1, increased by 40.7% and 40.3%. This paper provides valuable ideas for optimizing the properties of bulk TiZrV getters. [ABSTRACT FROM AUTHOR]

Copyright of Electronic Processing of Materials / Elektronnaya Obrabotka Materialov is the property of Institute of Applied Physics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The research results present the influence of nickel impurities introduced by diffusion into monocrystalline silicon on the characteristics of solar cells (SCs). It is established that doping with nickel atoms makes it possible to increase the lifetime of the MCCs in the material by up to a factor of two and the efficiency of SCs by 20–25%. It is shown that the distribution of nickel clusters in the volume of the material is almost uniform, and their size does not exceed 0.5 μm. The concentration of clusters in the volume is ~1011–1013 cm–3; and in the near-surface layer, ~1013–1015 cm–3. The physical mechanisms of the influence of the bulk and near-surface clusters of nickel atoms on the efficiency of silicon SCs are revealed. It is experimentally established that the decisive role in increasing their efficiency is played by the processes of gettering of recombination-active technological impurities by nickel clusters, occurring in the nickel-enriched front surface region of the SCs. [ABSTRACT FROM AUTHOR]

This study focuses on the enhanced passivation and gettering of boron‐doped p‐type solar grade silicon wafers by incorporating carrier‐selective and passivating tunnel oxide contact (TOPCon). A symmetrical stack of aluminum oxide (Al2O3)/p‐doped n‐type polysilicon (n‐poly‐Si)/ ultrathin silicon oxide (SiOx) in conjunction with long cycles of forming gas annealing is used for enhancing the silicon wafer quality with a novel approach. Multilayer of n‐poly‐Si/SiOx on p‐type crystalline silicon wafer exhibits an implied open‐circuit voltage (iVoc) of 726 mV, effective carrier lifetime (τeff) of 857 μs, and a low recombination current density (Jo) of 1.9 fA cm−2 when subjected to a postdeposition annealing (PDA) of phosphorus‐doped hydrogenated amorphous silicon (n‐a‐Si:H) at 820 °C. To boost passivation and gettering quality, 10 nm‐thick Al2O3 layers on both sides of n‐poly‐Si/SiOx samples are added. This leads to improved τeff (962 μs), reduced Jo (1.1 fA cm−2), and higher iVoc (728 mV). Herein, a thinner 50 nm n‐poly‐Si layer for improved properties is applied. The experiments show improved passivation and gettering. A Quokka‐3 simulation examines the potential of high‐efficiency p‐type TOPCon cells. A novel solar‐grade p‐type wafer quality enhancement approach is introduced, amalgamated with Quokka‐3 results, which could be a milestone in high‐efficiency p‐type TOPCon solar cell production. [ABSTRACT FROM AUTHOR]

An assessment of the bulk material quality of industrial Czochralski (Cz) grown phosphorus‐doped n‐type silicon (Si) wafers along an ingot is reported. The minority charge carrier lifetimes of the Cz‐Si wafer bulk before and after phosphorous (POCl3) diffusion gettering are assessed, by applying room‐temperature superacid surface passivation to avoid any additional gettering or hydrogenation effect. A substantial increase in the bulk lifetime of all of the n‐type Cz‐Si wafers along the ingot is observed, indicating the effectiveness of a gettering step for such wafers and the presence of getterable metallic impurities in these wafers. By experimentally monitoring the lifetime changes upon a gettering anneal and simulating the gettering kinetics based on different metal diffusivities, iron is identified to be a limiting defect, at least for the wafers from the tail part of the ingot. A dissolved iron concentration of (8±2) ×1011 cm−3$\left(\right. 8 \pm 2 \left.\right) \textrm{ } \times \left(10\right)^{11} \left(\text{ cm}\right)^{- 3}$ is estimated from the bulk lifetimes of the tail wafers. This lifetime kinetics approach is also a demonstration of a new method to identify iron, or other getterable metals with moderate diffusivities such as chromium, in n‐type silicon wafers. [ABSTRACT FROM AUTHOR]

Conventional silicon (Si) wafers are produced by energy‐intensive ingot crystallization which is responsible for a major share of a solar cell's carbon footprint. This work explores Si epitaxially grown silicon wafers (EpiWafers) that are produced by direct epitaxial deposition of trichlorosilane on a reusable substrate. This approach requires less energy and material and hence offers a potential for reduced cost and carbon footprint. Solar cells made from EpiWafers usually suffer from efficiency losses due to recombination at structural crystal defects associated with epitaxial growth. The nature of these defects is investigated and defects at the EpiWafer's back surface are critical. Most of these defects are highly recombination‐active, pairwise‐connected misfit dislocations in the <110> direction. They originate from a lattice mismatch between the highly doped substrate and the less‐doped epitaxially grown layer. In this contribution, the detrimental impact of these defects can be mitigated using typical manufacturing processes of high‐efficiency solar cells, such as KOH etching, gettering, and oxidation. Local minority charge carrier lifetimes as high as 2.2 ms after industrially feasible processes are reported. Simulations using efficiency‐limiting bulk recombination analysis implies that the material would allow conversion efficiencies of up to 25.6% considering tunnel oxide‐passivated contact acting as rear emitter solar cell design. [ABSTRACT FROM AUTHOR]

This study demonstrates that the concentration of nickel atoms near the surface of solar cells is 2-3 orders of magnitude higher than in the bulk material, significantly enhancing the gettering rate at the surface. Using IR-microscopy, SEM, and SIMS, we found that the surface density of nickel clusters is approximately 106-107 cm-2, with an average cluster diameter of 20-100 nm and a cluster concentration of 1011±1015 cm-3 Experimental results revealed that nickel clusters on the surface of silicon samples contain a substantial amount of oxygen and recombination impurities (Cu, Fe, Cr), indicating excellent gettering properties. We identified the physical mechanisms underlying the effects of nickel impurity atom diffusion and additional thermal annealing on the state of nickel atoms near the surface and base of the solar cells. Physical models were developed for the structure of nickel atom clusters in silicon and for the gettering process of fast-diffusing impurities by these clusters. The binding energy of fast-diffusing impurity atoms with a nickel cluster was estimated to be approximately 1.39 eV. Calculations indicated that nickel doping can increase the lifetime of minority charge carriers by a. factor of 2-4, and experimental results confirmed an increase in the lifetime of minority charge carriers by up to a. factor of 2. These findings highlight the potential of nickel doping to enhance the performance and efficiency of silicon-based solar cells, offering a promising avenue for future research and development in photovoltaic technology. [ABSTRACT FROM AUTHOR]

• Two-step annealing enhances oxygen precipitation, and thus reduce the recovery of minority carrier lifetime during phosphorus gettering. • The effectiveness of phosphorus gettering is influenced by the size and quantity of oxygen precipitates. This study investigates the effects of single-step and two-step annealing processes on the formation of oxygen precipitates and their impact on metal impurity gettering in gallium-doped monocrystalline silicon. The research focuses on the competitive relationship between internal gettering by oxygen precipitates and external gettering through phosphorus diffusion. Experimental results show that two-step annealing generates larger and more abundant oxygen precipitates, enhancing the internal gettering effect and reducing the recovery of minority carrier lifetime after phosphorus gettering. Despite this, phosphorus diffusion gettering remains effective in improving minority carrier lifetime, although the degree of improvement depends on the size and quantity of oxygen precipitates. These findings offer valuable insights for optimizing the fabrication process of silicon-based solar cells. [ABSTRACT FROM AUTHOR]

Phosphorus gettering using tubular diffusion furnaces was performed on n-type cast monocrystalline silicon wafers to assess its impact on wafer quality and the conversion efficiency of heterojunction solar cells. A comprehensive analysis of temperature, duration, and cooling rate in the diffusion process was conducted. The optimal parameters were identified at a temperature of 850 °C for 30 min, with a cooling rate of 5 °C/min down to 500 °C. This gettering process effectively reduced interstitial iron concentration, improved minority carrier lifetime, and increased the average efficiency of HJT cells by an absolute 0.4 %, with a 1.1 % increase for those made from bottom wafers with high metal concentration. [ABSTRACT FROM AUTHOR]

This study reports on the electronic properties of industrial phosphorus-doped n-type silicon ingots for photovoltaic applications grown using the Recharged Czochralski method. The electronic quality is assessed via carrier lifetime measurements, both directly on the ingots and on passivated wafers, and via implied open-circuit (i V O C), and implied maximum power point (i V M P P) voltages. The wafers are studied in the as-grown state, and after various high temperature steps, including Tabula Rasa , phosphorus diffusion gettering, and boron diffusion. The material exhibited very high bulk quality, with bulk lifetimes up to 8 ms at an injection level of 5 × 10 14 cm − 3 , and with i V O C (1-sun) values up to 750 mV , prior to any high temperature processing. A Tabula Rasa step did not significantly improve the wafer quality, indicating a low presence of oxygen-related defects in this material, consistent with the low interstitial oxygen content of below 5 × 10 17 cm − 3 . However, phosphorus diffusion gettering improved the wafer quality, especially towards the tail end of each ingot, and at lower injection levels near maximum power point. Phosphorus diffusion gettering increased the i V O C (1-sun) of the wafers by around 5 mV , approaching the Auger limit. Additionally, a boron diffusion step had minimal impact on the bulk lifetimes. Overall, our findings suggest that these RCz-grown n-type wafers exhibit very high quality, approaching the Auger limit near open-circuit, and are well-suited for high-efficiency solar cells without the need for additional high-temperature processing. • Assessing the material quality of n-type RCz industrial ingots, both directly on the ingot and on passivated wafers. • Bulk lifetimes of up to 8 ms and i V O C (1-sun) values up to 750 mV. • Low interstitial oxygen content of below 5 × 10 17 cm − 3 , low presence of oxygen-related defects. • Improvement of the wafer quality after gettering, particularly towards the bottom of each ingot, nearing the Auger limit. • No significant degradation after boron diffusion. [ABSTRACT FROM AUTHOR]

For the mass production of highly sensitive CMOS image sensors, the development of a high-performance gettering technique, which can remove metallic impurity contaminations from device active region with a low-concentration impurity such as carbon or oxygen is required. To address this issue, we developed a hydrocarbon (C 2 H x +) and silicon-hydride (SiH y +) mixture molecular ion implantation technique to form a gettering sink even under low carbon doses. However, the influence of carbon on gettering behavior in the molecular-ion-implanted region has never been investigated. In this study, we investigated the influence of the C 2 H x + ratio on the gettering behavior in the molecular-ion-implantation region by changing the cooling method in Ni contamination diffusion heat treatment between quenching and slow cooling. As a result, we clarified that the gettering behavior is dependent on the defect type that changes depending on the C 2 H x + ratio. These results suggest that mixture molecular ion implantation is effective in designing the gettering sinks via the changes in C 2 H x + ratio. [ABSTRACT FROM AUTHOR]

• Calculations demonstrate the tendencies to the formation stable pairs of interstitial boron and phosphorous impurities in silicon. • The nature of high solubility and mobility of transitional metals atoms in Si were revealed. • Simulations demonstrate affinity of Fe, Co, Ni to B and P defects. • The mechanism of destruction stable B-P pairs due to charge redistribution near metal impurity were proposed. In this work, we report the results of the systematic studies of the interactions between boron and phosphorous impurities in silicon matrix and transitional metals (TM) co-dopants: iron, cobalt, and nickel. Calculations results demonstrate the favorability of the stable pairs of substitutional boron and phosphorous defects. Calculated energies of the formation of substitutional and interstitial TM defects explain the high solubility and mobility of this kind of impurity. The simulations also reveal reciprocal affinity between B, P, and TM impurities that leads to the migration of metal atoms toward boron and phosphorous defects. Redistribution of the charge density caused by the presence of TM in the neighboring position leads to a significant decrease in the energy cost for the migration of B and P substitutional impurities to the interstitial void. [ABSTRACT FROM AUTHOR]