Light-induced activation and deactivation of bulk defects in boron-doped float-zone silicon

Abstract

In this paper, we present new insight in the degradation and subsequent recovery of charge carrier lifetime upon light soaking at 75 °C observed in float-zone silicon wafers. Variations of doping type, dielectric passivation schemes and thermal treatments after layer deposition were performed. The degradation was only observed for p-type float-zone silicon wafers passivated with passivation schemes involving silicon nitride layers. An influence of thermal treatments after deposition was found. N-type wafers did not degrade independent of their passivation scheme. Room temperature re-passivation experiments showed the degradation to affect the wafer bulk, and photoluminescence studies demonstrated fine lateral striations of effective lifetime. We conclude that the degradation is caused by bulk defects that might be related to hydrogen complexes

Superacid-Treated Silicon Surfaces: Extending the Limit of Carrier Lifetime for Photovoltaic Applications

“…Fig. 8(a) plots the injection-dependent bulk lifetime of an FZ p-type silicon wafer which has been passivated by a stack of Al 2 O 3 and a-SiN x :H and then subject to a rapid thermal anneal at 800°C and subsequently illuminated (0.1 W/cm 2 ) for 1-2 hours as outlined in [44]. Under these conditions, a significant reduction in lifetime is observed [compared to Fig.…”

“…8(b). In this case, the defect has been attributed to hydrogen complexes (from the dielectric stack) interacting with grown-in defects [44], which otherwise would have been difficult to determine without the SA treatment. We note, PL images are only quantitative if the passivation film is spatially uniform, which is the case for SA-treated silicon.…”

“…With the development of high-quality room temperature passivation schemes such as SA-treated silicon, low-temperature gettering and hydrogenation techniques can be developed [18]- [21], which otherwise would be difficult to measure, if, for example, these methods relied on SiN x and Al 2 O 3 passivation, which in themselves can introduce hydrogen or change bulk properties through annealing procedures to activate the surface passivation (i.e., 400°C) [44]- [46]. In this regard, the SA treatment can provide valuable information regarding passivation quality of dielectric films and their impact on the bulk material.…”

Temporary Surface Passivation for Characterisation of Bulk Defects in Silicon: A Review

“…Grant et al utilised the light enhanced HF passivation method to highlight the thermal instability in commercially available FZ silicon over the temperature range 80–1100 °C, which has led to an improved understanding of FZ silicon and how to thermally treat it . In a recent study, effective lifetime degradation was measured in illuminated FZ silicon passivated with an Al 2 O 3 ‐SiN x stack . This stack was etched away and the sample was then re‐passivated with a superacid thin film at room temperature with a similar S to the original passivation.…”

Eliminating Light-Induced Degradation in Commercial p-Type Czochralski Silicon Solar Cells

“…However, FZ silicon wafers are significantly more expensive than those produced from Cz silicon and hence not preferred by solar cell manufacturers. FZ silicon can also be subject to various other defects, such as nitrogen related defects or LID effects that can significantly reduce bulk lifetimes [32][33][34].…”