Concentrations and Reactions of Iron in Crystalline Silicon after Aluminum Gettering

Abstract

Iron is the most common transition metal impurities in semiconductor industry and PV silicon. Thus, it seems unlikely to avoid contamination with iron that has been considered to have the highest concentration in silicon wafers (Jastrzebski, et al., 1995). Unfortunately, less than 1ppb of iron was found to degrade the performance of p-type silicon device through the massive reduction of the minority carrier diffusion length (Buonassisi et al., described. Results and discussion are included in chapter 4. This chapter is divided into four parts; the influence of wet chemical etching on the iron concentration in silicon as well as the correspondence between time of etching, different etchants and boron passivation profile are studied in the first part. The second part deals with the aluminum gettering of iron in silicon and the physical mechanisms relevant for such temperature-dependent segregation coefficient in order to increase the understanding of the abilities and limitations of aluminum gettering in silicon solar cell processing, while the third part treats various aspects of aluminum gettering induced vacancies and using several ways to monitor vacancy concentration such as platinum and gold diffusion. Based on these finding, the last part in this thesis investigates the interaction between iron and induced vacancies from aluminum gettering under light illumination. Particular attention is devoted to gettering of iron and the interplay with vacancy, as well as to the influence of light on the formation of iron vacancy complexes (FeD). Finally, the main ideas of the thesis are summarized along a short conclusion and outlook in chapter 5.