Imaging the band-to-band photoluminescence of silicon wafers is known to provide rapid and high-resolution images of the carrier lifetime. Here, we show that such photoluminescence images, taken before and after dissociation of iron-boron pairs, allow an accurate image of the interstitial iron concentration across a boron-doped p-type silicon wafer to be generated. Such iron images can be obtained more rapidly than with existing point-by-point iron mapping techniques. However, because the technique is best used at moderate illumination intensities, it is important to adopt a generalized analysis that takes account of different injection levels across a wafer. The technique has been verified via measurement of a deliberately contaminated single-crystal silicon wafer with a range of known iron concentrations. It has also been applied to directionally solidified ingot-grown multicrystalline silicon wafers made for solar cell production, which contain a detectible amount of unwanted iron. The iron images on these wafers reveal internal gettering of iron to grain boundaries and dislocated regions during ingot growth.

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Objective Prolonged home isolation may lead to long-term negative consequences for both children and caregivers’ psychological wellbeing, especially in families with children with neurodevelopmental disorders. Therefore, a scoping review was conducted to identify challenges faced by caregivers of children with neurodevelopmental disorders during the coronavirus disease 2019 (COVID-19) pandemic and to consolidate parenting interventions and guidelines. Methods A systematic search was conducted on Embase, PsycInfo, PubMed, Scopus, and LitCovid. All article types published between December 2019 and November 2020 which reported on intervention guidelines and experiences of families with children with neurodevelopmental disorders during the COVID-19 pandemic were included. Qualitative themes, quantitative data, and article summaries were charted, and a thematic analysis was conducted. Results Twenty-nine articles were included in the review. Three themes were generated: (a) behavioral issues and health concerns, (b) disruptions of lifelines and daily routines, and (c) existing programs, models, and guidelines to support families. Additionally, a list of caregiver strategies such as scheduling regular online consultations, maintaining online therapy, educating a child on COVID-19, and preventive behaviors, creating a structured daily schedule and reinforcement system, and selecting child-appropriate activities was consolidated. Conclusion This review revealed a lack of evidence-based studies and articles on children with other neurodevelopmental disorders apart from autism and attention-deficit hyperactivity disorder. It also places emphasis on the importance of telehealth services as major lifelines to parents during this pandemic and urges healthcare organizations to provide funding to increase telehealth services to afflicted families.

We report on a procedure to temporarily attain a very high level of surface passivation for silicon wafers at room temperature. When applied during a photoconductance measurement, the procedure permits an accurate assessment of the bulk lifetime, even for high-lifetime samples (τbulk > 5 ms) that are otherwise difficult to measure. It is already established that the surfaces of a silicon wafer can be well passivated by immersion in hydrofluoric acid (HF). Here, we show that the HF passivation is greatly enhanced by illuminating the wafers just prior to measurement, and that the HF passivation depends critically on the surface preparation, where the best passivation is attained after etching the wafers in tetramethylammonium hydroxide. We assess the level of passivation for a range of HF concentrations and wafer resistivities, and we demonstrate that S < 5 cm/s can be attained on 0.8–1000 Ω-cm n- and p-type silicon wafers. We demonstrate the value of the method with two examples.

We report the changes with lattice isotope of the energies of the zero-phonon lines (ZPLs) and some of the local vibrational modes (LVMs) of commonly encountered radiation-damage centers in silicon. On changing from nat Si to 30 Si, ZPLs of the different centers shift by +0.8 to +1.8 meV. The carbon-oxygen "C" center is taken as the primary example. For this center, the measured changes in the frequencies of the LVMs in the electronic ground state of the center agree closely with the results of density functional theory (DFT). We suggest that the LVM frequencies in the excited state can be obtained from DFT calculations of the positive charge state. The effect on the ZPL is broken into three parts. The dependence of the ZPL on the isotopically induced change in the LVMs and in the lattice volume is shown to be small compared to the effects of the electron-phonon coupling to the continuum of lattice modes. This dominant effect can be found, in principle, from the temperature dependence of the energy of the ZPL, but data can only be measured over too small a temperature range. We suggest that an estimate of the isotope effects can be derived by rescaling the appropriate data for the indirect energy gap. This simple empirical approach reproduces the measured isotope shifts of the ZPLs of the "C" and "P" centers within ϳ10%, of the "I" and "T" centers within ϳ30%, and within a factor of 2 for the "G" center.

Abstract-In this paper, we present a new method to determine the simultaneous injection and temperature dependence of the sum of the majority and minority carrier mobilities in silicon wafers. The technique is based on combining transient and quasi-steadystate photoconductance measurements. It does not require a full device structure or contacting but only adequate surface passivation. The mobility dependence on both carrier injection level and temperature, as measured on several test samples, is discussed and compared with well-known mobility models. The potential of this method to measure the impact of dopant concentration, compensation ratio, injection level, and temperature on the mobility is demonstrated.

The electronic properties of multi-crystalline silicon must be improved during solar cell fabrication if highly efficient devices are to be made. This work shows how gettering and silicon nitride induced hydrogenation improve three properties: carrier lifetime, interstitial iron concentration, and trap density. Area averaged effective carrier lifetimes less than 10 ms were improved to greater than 60 ms. A tenfold reduction in trap densities was achieved. Photoluminescence images showing the influence processing techniques have on the electronic properties of the silicon are presented.

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