Characterization of Oxidation-Induced Stacking Fault Rings in Cz Silicon: Photoluminescence Imaging and Visual Inspection After Wright etch

AbstractOxidation-induced stacking fault rings in polished Cz silicon samples before and after thermal wet oxidation are investigated by use of photoluminescence imaging. Currently the standard procedure for OSF ring detection is to expose the samples to a toxic preferential etchant, e.g. a Wright solution, after a thermal oxidation. This solution primarily attacks the regions with stacking faults, allowing detection by visual inspection. Samples from the seed end of p-type Cz silicon ingots with resistivities of approximately 1Ohm-cm were measured by PL imaging before and after a thermal oxidation process. Subsequently, Wright-etching was performed on the oxidized samples to expose stacking faults. The lifetime variations in the PL images were correlated with the location of the rings in the preferentially etched surfaces, and good agreement was found. The results show that for this crystal pulling process, even the PL images of unpassivated polished samples can be used to detect the OSF ring location. The thermal oxidation at 1100°C enhanced the contrast between the OSF ring and the rest of the sample in the PL image

Sticky stories from the classroom: from reflection to diffraction in early childhood teacher education

This article aims to challenge the prominence of reflexivity as a strategy for early childhood teachers to adopt by taking Norwegian early childhood teacher education as its focus. Observed micro-moments from a university classroom generate multilayered, multi-sensorial entangled narratives that address what reflection and diffraction are and what they do – where students, the educator, materiality, space and affects intra-act. Furthermore, the article explores the ways in which teacher educators and students in early childhood teacher education become-with the classroom and materiality, and, in doing so, ideas about professionalism in early childhood education are opened out. By identifying the limitations of reflection, the authors go on to explore what working with diffraction might offer to reach alternative understandings. By placing a focus on seemingly unremarkable and routine events in the life of an early childhood teacher education classroom, the authors offer other, potentially more generative ways to think about student teachers and their further professional practice in kindergartens

Off-axis measurements on a mm-wave optically controlled lens antenna

We present initial experimental data demonstrating the off-axis scanning performance and beam fidelity of a range of optically controlled transmission-type photo-injected Fresnel zone plate antenna (tx-piFZPA) designs at 94 GHz, based on a novel architecture. Several tx-piFZPA designs were characterized at a range of off-axis beam locations, up to 45° from boresight. Initial results indicate scan losses up to 5 dB at 10° deflection and increasing up to 12 dB at 45° deflection, across several tx-piFZPA designs. In addition, measured tx-piFZPAs have demonstrated highly repeatable and precise beam control, achieving a minimum pointing resolution of Δθ = 0.0005°. The piFZPA method proves to be a promising cost-effective nonmechanical beam-steering solution for high millimeter- and terahertz-frequency applications.</p

Distribution of radiative crystal imperfections through a silicon ingot

Crystal imperfections limit the efficiency of multicrystalline silicon solar cells. Recombination through traps is more prominent in areas with high density of crystal imperfections. A method to visualize the distribution of radiative emission from Shockley Read Hall recombination in silicon is demonstrated. We use hyperspectral photoluminescence, a fast non-destructive method, to image radiatively active recombination processes on a set of 50 wafers through a silicon block. The defect related emission lines D1 and D2 may be detected together or alone. The D3 and D4 seem to be correlated if we assume that an emission at the similar energy as D3 (VID3) is caused by a separate mechanism. The content of interstitial iron (Fei) correlates with D4. This method yields a spectral map of the inter band gap transitions, which opens up for a new way to characterize mechanisms related to loss of efficiency for solar cells processed from the block

Identification of defects causing performance degradation of high temperature n-type Czochralski silicon bifacial solar cells

Four industrial-scale n-type Czochralski silicon crystals were grown with different impurity contents, i.e. metallics, phosphorus and oxygen. Horizontal slices were obtained from the top and middle of the crystals and were characterized in terms of lifetime and both defect and impurity distribution. The slabs characterization was performed both under as-grown conditions and after 2-step oxidation. Solar cells were fabricated from neighboring wafers with n-PASHA process and the overall efficiency determined. The crystal grown under low oxygen incorporation conditions has shown higher average as-grown lifetimes compared to the other crystals. The addition of lower phosphorus concentration to the melt resulted in an improvement of the lifetime of the crystal while the use of low grade feedstock has mainly affected the quality at the middle of the corresponding crystal. However, the major difference between top and middle heights was still the interstitial oxygen concentration for all crystals under investigation. The distribution of the interstitial oxygen concentration has not shown significant fluctuations through the samples radial direction. In addition, significant void fluctuations were found through the slabs radial direction, and demonstrate possible variations in the vacancy incorporation at the solidification interface during crystal growth. After heat treatment, large fluctuations of the lifetime were found through the samples radial direction, and are mainly associated to the local fluctuations of the oxygen precipitate density. However, these variations were suppressed in the crystal of lower oxygen incorporation. Solar cells performance degradation was mainly correlated with oxygen precipitation during their fabrication. It was also demonstrated that their efficiency is largely affected by the formation of detrimental striations of high periodicity. Their formation was thus associated to fluctuations of the vacancy concentration due to transient growth and their interaction with oxygen during crystal cooling. These oxygen nuclei may grow during solar cells processing and become even more detrimental to their performance