Modulating the extent of fast and slow boron-oxygen related degradation in Czochralski silicon by thermal annealing: Evidence of a single defect

Abstract

The fast and slow boron-oxygen related degradation in p-type Czochralski silicon is often attributed to two separate defects due to the different time constants and the determination of different capture cross section ratios (k). However, a recent study using high lifetime samples demonstrated identical recombination properties for the fast and slow degradation and proposed an alternative hypothesis that these were in fact due to a single defect. The study presented in this article provides further experimental evidence to support the single defect hypothesis. Thermal annealing after light soaking is used to investigate the behaviour of subsequent boron-oxygen related degradation. Modifying the temperature and duration of dark annealing on pre-degraded samples is observed to alter the fraction of fast and slow degradation during subsequent illumination. Dark annealing at 173 °C for 60 s is shown to result in almost all degradation occurring during the fast time-scale, whereas annealing at 155 °C for 7 h causes all degradation to occur during the slow time-scale. This modulation occurs without changing the total extent of degradation or changing the capture cross-section ratio. The results are consistent with the fast decay being caused by defect formation from immediately available defect precursors after dark annealing, whereas the slow degradation is caused by the slow transformation of another species into the defect precursor species before the more rapid reaction of defect formation can proceed.

Boron–Oxygen Complex Responsible for Light‐Induced Degradation in Silicon Photovoltaic Cells: A New Insight into the Problem

“…[2,6,37] The ratio of electron to hole capture cross sections for the donor level has been found to be in the range between 10 and 20. [6,37] Assuming physically feasible maximum values for σ n and the observed lifetime changes, observation of the responsible SRH center using standard techniques, such as DLTS and MCTS, [10][11][12] should present no difficulty. We have carefully examined the DLTS and MCTS spectra of the Cz-Si:B samples subjected to the LID treatments, and in consistency with the previously published results, Markevich et al [38] have not observed emission signals from deep-level defects, which have been argued to be responsible for the LID.…”

“…In boron‐doped silicon crystals grown by the Czochralski technique (Cz‐Si), there are two families of defects, which have been known for many years but still lack proper understanding and identification. These are 1) electron traps which were reported by Hornbeck and Haynes in 1955, and 2) defects responsible for light‐induced degradation (LID) of solar cells fabricated from silicon materials containing boron and oxygen atoms …”

“…These are 1) electron traps which were reported by Hornbeck and Haynes in 1955, [1] and 2) defects responsible for light-induced degradation (LID) of solar cells fabricated from silicon materials containing boron and oxygen atoms. [2][3][4][5][6] The information on electron traps observed by Hornbeck and Haynes is very limited. [1,[7][8][9] The authors reported long (minutes) two-stage decays of conductivity at room temperature in boron-doped Si crystals after the application of short light pulses.…”

“…This latter process is temperature dependent which has been characterized in terms of the formation of a recombination active defect with an activation energy of 0.48 eV . There is some debate as regards to the relationship between the fast and slow process, with arguments for the two processes being independent or originating from a common defect . However, the slow degradation is by far the most significant and is predominantly responsible for the loss of efficiency.…”

Vertically integrated modeling of light-induced defects: Process modeling, degradation kinetics and device impact

“…While the present study focused largely on Cu-LID, there are other examples of light-induced defects that are wellunderstood that could be coupled into a similar simulation tool, such as: the boron-oxygen (BO) complex [14,16,[28][29][30][31][32] and Fe-B pair-dissociation [35]. While this approach is not directly applicable to light-induced defects without an established physical root cause, such as the so called Light and Elevated Temperature Induced Degradation (LeTID) [1][2][3], this approach can be used to rule out root causes of unknown LID phenomena, and thus help concentrate research efforts elsewhere.…”