Bulk minority carrier lifetimes and doping of silicon bricks from photoluminescence intensity ratios

Abstract-Photoluminescence-based imaging is most commonly used to measure the excess minority carrier density and its corresponding lifetime. By using appropriate surface treatments, this high-resolution imaging technique can also be used for majority carrier concentration determination. The mechanism involves effectively pinning the minority excess carrier density, resulting in a dependence of the photoluminescence intensity on only the majority carrier density. Three suitable surface preparation methods are introduced in this paper: aluminum sputtering, deionized water etching, and mechanical abrasion. Spatially resolved dopant density images determined using this technique are consistent with the images obtained by a well-established technique based on free carrier infrared emission. Three applications of the technique are also presented in this paper, which include imaging of oxygenrelated thermal donors, radial dopant density analysis, and the study of donor-related recombination active defects. These applications demonstrate the usefulness of the technique in characterizing silicon materials for photovoltaics.

Section: Numerical Model Predictionsmentioning

confidence: 99%

Applications of Photoluminescence Imaging to Dopant and Carrier Concentration Measurements of Silicon Wafers

Lim

Forster²,

Zhang

et al. 2013

“…3). The spectral PLIR method has been described previously in [31] and [32]. It utilizes the bulk lifetime-dependent shift in spectral PL emission to quantify the silicon minority carrier bulk lifetime.…”

Section: B Spectral Photoluminescence Intensity Ratio and Bulk Lifetmentioning

confidence: 99%

“…These relative functions are normally used to determine the PLIR to bulk lifetime transfer function through taking the ratio of the individual transfer functions (see [31] and [32]). Hence, we first measure the brick in full field without any masking and analyze its bulk lifetime using the standard spectral PLIR method.…”

Section: A Quantitative Analysis Of Low-lifetime Bottom Section-extementioning

confidence: 99%

“…This paper extends the use of PL imaging from the measurement of the interstitial iron concentration on passivated silicon wafers [25], [30] to measuring directly on the unpassivated brick surface. We demonstrate the measurement of bulk lifetimes on unpassivated surfaces before and after iron-boron (Fe-B) pair dissociation using the spectral photoluminescence intensity ratio (PLIR) analysis [31], [32]. Experimental work is performed on directionally solidified boron-doped silicon bricks, as it is the most widely used type of ingot crystallization in the photovoltaic industry [33].…”

mentioning

confidence: 99%

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Imaging As-Grown Interstitial Iron Concentration on Boron-Doped Silicon Bricks via Spectral Photoluminescence

Mitchell

Macdonald

Schön

et al. 2014

Self Cite

Abstract-The interstitial iron concentration measured directly on the side face of a silicon brick after crystallization and brick squaring can give important early and fast feedback regarding its material quality. Interstitial iron is an important defect in crystalline silicon, particularly in directionally solidified ingots. Spectral photoluminescence intensity ratio imaging has recently been demonstrated to independently provide high-resolution bulk lifetime images and is therefore ideally suited to assess spatially variable multicrystalline silicon bricks. Here, we demonstrate this technique to enable imaging of the interstitial iron concentration on boron-doped silicon bricks and thick silicon slabs. We present iron concentration studies for two directionally solidified silicon bricks of which one is a standard multicrystalline and the other is a seeded-growth ingot. This lifetime-based measurement technique is highly sensitive to interstitial iron with detection limits down to concentrations of about 1 × 10 10 cm −3 . Its accuracy is enhanced, as the injection level remains below 2 × 10 12 cm −3 during the measurement and, hence, avoids the influence of injection level dependences on the conversion factor, although it remains dependent on the knowledge of the electron capture cross section of interstitial iron in silicon. Access to both bulk lifetime and dissolved iron concentration provides a valuable parameter set of as-grown crystal quality and the relative recombination fraction of interstitial iron via Shockley-Read-Hall (SRH) analysis. Simulated interstitial iron concentration profiles support the presented experimental data.Index Terms-Bricks, dissolved iron, imaging, ingot, interstitial iron, photoluminescence (PL), silicon.

“…Würfel et al [1] first developed an approach to extract the minority carrier diffusion length from PL spectra. Later works derived from this approach have been applied for both silicon wafers [2]- [4] and bricks [5]- [7] to separate the effects of bulk and surface recombination at room temperature. In addition, Schinke et al [8] modeled PL spectra for different surface morphologies, and Barugkin et al [9] employed spectral PL measurements to quantify the light trapping for various plasmonic structures.…”

Section: Introductionmentioning

confidence: 99%

Impact of Carrier Profile and Rear-Side Reflection on Photoluminescence Spectra in Planar Crystalline Silicon Wafers at Different Temperatures

Nguyen

Rougieux

Baker-Finch

et al. 2015

Abstract-The increasing use of spectral photoluminescence as an advanced and accurate diagnostic tool motivates a comprehensive assessment of the effects of some important optical and electrical properties on the photoluminescence spectra from crystalline silicon wafers. In this paper, we present both modeling results and measurements to elucidate the effects of the internal reflectance at the planar wafer surfaces, as well as the carrier profile varying across the sample thickness due to an increased rear-surface recombination velocity, as a function of temperature. These results suggest that the accuracy of existing spectral PL techniques may be improved by using higher temperatures due to the increased effect of the carrier profile at higher temperatures. They also show that changes in the photoluminescence spectrum shape caused by the addition of a rear-side specular reflector offset those caused by changes in the carrier profile due to increased rear surface recombination, and therefore, considerable care needs to be taken when changing the rear-side optics. Finally, the possible impact of variations in the rear-side reflectance on the band-band absorption coefficient and radiative recombination coefficient, which have previously been determined using the spectral photoluminescence technique, is assessed and demonstrated to be insignificant in practice.