Czochralski‐grown gallium‐doped silicon wafers are now a mainstream substrate for commercial passivated emitter and rear cell (PERC) devices and allow retention of established processes while offering enhanced cell stability. We have assessed the carrier lifetime potential of such Czochralski‐grown wafers in dependence of resistivity, finding effective lifetimes well into the millisecond region without any gettering or hydrogenation processing, thus demonstrating one advantage over boron‐doped silicon. Second, the stability of gallium‐doped PERC cells are monitored under illumination (>3000 h in some cases) and anomalous behavior is detected. While some cells are stable, others exhibit a degradation then recovery, reminiscent of light and elevated temperature‐induced degradation (LeTID) observed in other silicon materials. Surprisingly, cells from one ingot exhibit LeTID‐like behavior when annealed at 300 °C but near stability when not annealed, but, for another ingot, the opposite is observed. Moreover, a stabilization process typically used to mitigate boron–oxygen degradation does not influence any cells that are studied. Secondary‐ion mass spectrometry of the PERC cells reveals significant concentrations of unintentionally incorporated boron in some cases. Nevertheless, even in the absence of mitigating light‐induced degradation, Ga‐doped silicon is still more stable than unstabilized B‐doped silicon under illumination.

In this work, the established method of iron imaging is transferred from B‐doped silicon to Ga‐doped material. For this purpose, the pairing and splitting conditions are investigated and a preparation procedure suggested that ensures a sufficient fraction of iron–gallium pairing and splitting, respectively. Furthermore the defect parameters available in literature are compared and evaluated for a suitable description of the injection dependent carrier lifetime measurements. A parameter set that enables a coherent and adequate iron evaluation is suggested. Thus, a robust method for spatially resolved determination of the interstitial iron concentration in Ga‐doped silicon wafers is presented.

The response of lifetime samples made from boron‐ and gallium‐doped Czochralski‐grown silicon from the same producer to light‐ and elevated temperature‐induced degradation (LeTID) conditions (varying illumination at 75 °C), to dark anneals (DAs) at 175 °C, and the temporary recovery (TR) reaction under different conditions is investigated. It is found that Ga‐doped samples behave very differently than their B‐doped counterparts: while the carrier lifetime remains at a high level if an illumination equivalent to 1 sun at 75 °C is applied, strong carrier lifetime degradation occurs at low light intensities. A capture cross‐sectional ratio in degraded Ga‐doped samples of ~26 is found, which is typical for the LeTID defect. TR of this degraded state is observed on Ga‐doped samples when the illumination intensity is increased at 75 °C and when samples are illuminated at 25 °C with intermediate intensity. During DA of B‐doped samples, a bulk‐related degradation and a subsequent surface‐related degradation are observed. In contrast, degradation of Ga‐doped samples during DA only occurs on long timescales, and its cause is not clear, yet. It is concluded that the specific dopant species plays an active role both during LeTID and for surface‐related degradation—possibly as a result of differences in the acceptor–hydrogen pair properties.

Gallium-doped silicon material has been rapidly gaining importance in the photovoltaic industry as a boron-oxygen defect-free material with promising minority carrier lifetime. We investigate the influence of different cell process flows [passivated emitter and rear cell tunneling-oxide-passivating contact, and a "hot oxidation" process] on the bulk material quality of an industrial Ga-doped Cz-grown silicon material, as well as its lightand elevated temperature induced degradation degradation behavior under light at elevated temperature. We measure a generally high carrier lifetime level, which remains limited by an unknown recombination-active defect after most processes. Hydrogenation seems to passivate this unknown defect. In addition, we demonstrate that such high-quality p-type material can suffer noticeably by iron even for extremely low concentrations below 10 9 at/cm 3 .