Abstract
Herein, the effects of gettering, temperature, dopant concentration, and metal contamination on the etch pit density (EPD) of an mc‐Si material are studied. It is demonstrated that there is a reduction of EPD after gettering that is independent for varying etchants, thereby confirming the physical nature of this effect. The EPD analysis of wafers that are gettered on one wafer side, results in different EPD values for the two wafer sides. This finding constrains the possibilities for mechanisms of EPD reduction. The combined evidence of the experiments presented here supports the hypothesis that EPD reduction happens because the defect etching process for impurity‐lean dislocations is different from dislocations decorated with impurities.
Highlights
The technique of atmospheric pressure chemical vapor deposition (APCVD) allows for cost-effective approaches to passivated emitter, rear totally diffused (PERT) and other advanced solar cell concepts
Measurements of τeff, [Fei], and etch pit density (EPD) are used to compare sister wafers in the as-grown state on the one hand with samples that were subjected to gettering on the other hand and with samples subjected to the temperature load of the gettering process (Figure 3)
EPD measurements after Secco etch, executed on the P-gettered wafer side, show that low lifetime and high [Fei] regions typically correlate with regions of high EPD and that such regions remain inferior to their surroundings after co-gettering.[16]
Summary
The technique of atmospheric pressure chemical vapor deposition (APCVD) allows for cost-effective approaches to passivated emitter, rear totally diffused (PERT) and other advanced solar cell concepts. Co-diffusion gettering is known to increase the material quality of multicrystalline silicon,[1] and gettering[2] of the mc-Si material by means of phosphorous- [3,4] and boron-diffusion[5] are well researched. Effects of phosphorous diffusion gettering on metallic contaminations have been studied and correlated with measurements of etch pit density (EPD),[6] there is a lack of literature on the interplay of gettering procedures with EPD measurements. While significant mobility of dislocations in the silicon crystal is expected only for temperatures much closer to the melting temperature[7] than what was used in the high temperature steps of this work, EPD seems to be affected by P-diffusion gettering processes.[8,9]
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