Analysis of Lifetime-Limiting Defects in Cast-Mono Silicon Using Injection-Dependent Lifetime Spectroscopy Methods

Seed-assisted cast-mono silicon for photovoltaic (PV) application is a relevant alternative to the conventional Czochralski (Cz) in terms of cost and carbon footprint. Despite the remarkable PV conversion efficiencies reached when combining this material with novel cell concepts, cast-mono industrial deployment is infringed by the propagation of dislocation clusters during crystallization, inducing variations in final wafers quality. Indeed, some wafers feature dislocation-rich regions whose recombination activity is not fully understood. This article aims at providing insights into the carrier recombination in such regions. We focus on n-type cast mono grown from a compensated feedstock in order to obtain samples with the same crystallographic properties but different electron concentration (n
₀
) values. The bulk carrier lifetime in the dislocation-rich region could be approximated by the combination of two discrete defects for which the symmetry factor k could be estimated first by exploiting the relationship between the defect lifetime gradient with 1/n
₀
. Both defects energy positions (E
_T
) could be obtained, thanks to the defect parameter surface solution method. We analyzed the variations of the first defect Shockley-Read-Hall (SRH) parameters (E
_T
, k, and hole lifetime constant τ
_p
0
) with n
₀
and for temperatures ranging from 30 to 75 °C. A temperature-assisted transition of the first defect from one state to another was highlighted and was found to be enhanced by low n
₀
values. For each state, the SRH parameters were extracted.