Investigation of light-induced degradation in gallium- and indium-doped Czochralski silicon.

Light-induced degradation (LID) in boron (B)-doped Czochralski (Cz) silicon wafers has impacted commercial p -type silicon solar cells for decades. Substitution of boron with gallium (Ga) or (to a lesser extent) indium (In) has been suggested as a method to tackle this problem since Ga- and In-doped Cz wafers were shown to be less prone to LID. Although less prone to LID, several studies have reported some LID in these materials. In this study, LID in Ga- and In-doped Cz wafers is investigated. First, it is shown that LID is present in both materials. The degradation has two stages (fast and slow) for Ga-doped wafers and one stage for In-doped wafers. By performing the degradation at different temperatures, the activation energy of the defect formation is determined to be 0.74 ± 0.10 eV for the slow step in Ga-doped and 0.91 ± 0.15 eV for In-doped wafers. We then investigate defect deactivation with dark annealing. Both Ga- and In-doped wafers demonstrate a two-stage defect deactivation. Similar to defect formation, the defect deactivation activation energies are determined and reported. Finally, the focus is shifted to investigating the degradation mechanism in Ga-doped wafers, since they are currently the dominating wafer substrate for photovoltaic applications. It is shown that a three-state mechanism ("annealed", "degraded", and "stabilised"), similar to boron-oxygen (BO)-related defects, can explain their degradation. It seems the four-state model, suggested for the light- and elevated temperature-induced degradation, is not suitable for describing the degradation in Ga-doped Cz wafers. • Ga-doped Cz wafers have a two-stage LID process. • A two-stage defect deactivation is observed for both Ga- and In-doped wafers. • The activation energy of defect formation and deactivation for Ga- and In-doped wafers is measured. • A three-state model is presented to describe LID in Ga-doped wafers. [ABSTRACT FROM AUTHOR]