Deep carrier traps in as grown isotopically pure ²⁸Si FZ crystal

Abstract

We studied a distribution of dopants and carrier traps in the FZ grown 28 Si crystal. Samples cut-out from various parts of an as-grown crystal were analysed by deep level transient spectroscopy (DLTS) and photoluminescence (PL). Several traps were detected at the concentration level of $10 10 cm À3 by DLTS. Careful analyses of the obtained signals allow attributing the related traps to agglomerates of intrinsic defects. A correlation of the trap concentration to the phosphorus doping, detected by PL and confirmed by electric measurements was also observed. A possible attribution of the traps to the previously reported defects will be discussed.

Location and Properties of Carrier Traps in mc‐Si Solar Cells Subjected to Degradation at Elevated Temperatures

“…These observations can be correlated with previously reported degradation mechanisms, and with induced carrier traps in FZ‐Si annealed at higher temperatures . Very similar traps were also observed in FZ‐Si crystals that were quenched to room temperature from 800 °C after crystal growth . Recently, it was reported that the preannealing of mc‐Si cells in the dark at temperatures of 75–170 °C for several hours causes a degradation of the cell efficiency and affects further the LeTID process .…”

“…[24] Since the FZ-Si growth process excludes the incorporation of metal contaminants in significant concentrations, the origin of the traps is supposed to be related to the agglomerates of intrinsic defects (vacancies and/or interstitials) formed with participation/assistance of nitrogen and/or hydrogen. An increased defect concentration in FZ-Si crystals was detected at locations where dopant concentrations were higher (see previous studies [22,24,26] ). The similarity of LeTID-related defects to those formed in FZ-Si [17] may also originate from an enhanced density of intrinsic defects and dopants in striations of FZ-Si crystals.…”

“…We also checked the depth distribution of the trap density and the dependence of the peak amplitude from charging pulse duration ΔC(t P ). From the ΔC(t P ) dependencies, it was concluded that all hole-traps originated from extended defects, while the electron-traps showed the dependence of point-like defects (see, e.g., Fig 1 in the study by Mchedlidze et al [26] ). We did not detect a significant variation of the trap densities with depth from the n þ p-junction.…”

“…Interestingly, in most publications about traps in Fz-Si, a correlation of the trap density with the dopant level in the samples is reported. Since 2015, [21] several publications (see previous studies [22][23][24][25][26]41] and references therein) report on the formation of deep traps in FZ-Si bulk samples subjected to an annealing treatment at temperatures in the range of 400-800 C [23] and/or an annealing at %75 C under illumination. [24] Since the FZ-Si growth process excludes the incorporation of metal contaminants in significant concentrations, the origin of the traps is supposed to be related to the agglomerates of intrinsic defects (vacancies and/or interstitials) formed with participation/assistance of nitrogen and/or hydrogen.…”

“…[21][22][23][24][25] Very similar traps were also observed in FZ-Si crystals that were quenched to room temperature from 800 C after crystal growth. [26] Recently, it was reported that the preannealing of mc-Si cells in the dark at temperatures of 75-170 C for several hours causes a degradation of the cell efficiency and affects further the LeTID process. [27] Preannealing in the dark at T ≥ 75 C not only accelerates the subsequent LeTID degradation but also activates new defects.…”