Light Induced Curing (LIC) of Passivation Layers Deposited on Native Silicon Oxide

Joos, Sebastian; Herguth, Axel; Hess, Uwe; Ebser, Jan; Seren, Sven; Terheiden, Barbara; Hahn, Giso

doi:10.1016/j.egypro.2012.07.075

Cited by 11 publications

(8 citation statements)

References 7 publications

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“…This lifetime recovery effect for p-type samples under illumination has been reported previously for plasma-assisted ALD Al 2 O 3 films on the same substrates after firing [70]. A similar effect with the same trends for p-and n-type samples has also been reported for SiO x /SiN x stacks [162]. It is clear that the effect is not related to bulk contamination by iron [163], because the lifetime increase occurs more or less uniformly across the whole injection range (Fig.…”

Section: Effect Of Post-firing Illuminationsupporting

confidence: 88%

New Perspectives on Surface Passivation: Understanding the Si-Al2O3 Interface

Black

2016

Springer Theses

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High-efficiency crystalline silicon solar cells must suppress recombination at their p-type surfaces. Thin-film, amorphous aluminium oxide (Al 2 O 3) has been shown to provide very effective passivation of such surfaces, assisted by its negative fixed charge. However, many details of Al 2 O 3 passivation remain poorly understood. Furthermore, conventional means of depositing passivating Al 2 O 3 are too slow or too expensive to be suitable for high-volume commercial production. This thesis addresses these issues in three ways: 1) by contributing to a deeper understanding of semiconductor-dielectric interfaces and semiconductor surface recombination mechanisms in general, 2) by investigating the properties of Al 2 O 3 as a passivating dielectric for silicon surfaces, and 3) by demonstrating the viability of APCVD as a high-throughput, industrially compatible deposition method for Al 2 O 3 , enabling its application to commercial solar cells. Using Al 2 O 3 as a test case, it is shown how a novel analysis of the extended conductance method can be used to i) distinguish the separate contributions to the interface state distribution at a semiconductor-dielectric interface, and ii) determine their capture cross-sections for both minority and majority carriers. Furthermore, the direct link between these measured interface state properties and the recombination rate at the semiconductor surface is experimentally demonstrated by showing that the former can be used to accurately predict the latter. Investigations of the surface passivation properties of Al 2 O 3 reveal a remarkably consistent picture. It is shown that the properties of the Si-Al 2 O 3 interface states are essentially independent of the Al 2 O 3 deposition conditions and technique. The interface properties are found to be independent of the surface dopant concentration at boron-and phosphorus-doped surfaces, while recombination is shown to be only weakly dependent on surface orientation and morphology as a result of the remarkable orientation-independence of the Si-Al 2 O 3 interface state properties. Meanwhile, the chemical origin of the charge at the Si-Al 2 O 3 interface is elucidated by correlating FTIR and electrical measurements. xi xii APCVD is clearly shown-for the first time-to be capable of depositing Al 2 O 3 films with exceptional surface passivation properties, comparable to the best results achieved using other deposition techniques. In the best case, interface state densities as low as 5 × 10 10 eV −1 cm −2 at midgap, and negative fixed charge concentrations of 3.3 × 10 12 cm −2 are measured, resulting in a saturation current density of 7 fA cm −2 on undiffused p-type surfaces. The APCVD films are shown to be thermally stable under standard solar cell processing conditions and are demonstrated in large-area solar cells with peak efficiencies of 21.3 %. These results demonstrate the viability of APCVD Al 2 O 3 as a surface passivation layer for industrial silicon solar cells.

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Section: Effect Of Post-firing Illuminationsupporting

confidence: 88%

New Perspectives on Surface Passivation: Understanding the Si-Al2O3 Interface

Black

2016

Springer Theses

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“…This lifetime recovery effect for p-type samples under illumination has been reported previously for PA-ALD Al 2 O 3 films on the same substrates after firing [14]. A similar effect with the same trends for p-and n-type samples has also been reported for SiO x /SiN x stacks [29]. It is clear that the effect is not related to bulk contamination by iron [30], because the lifetime increase occurs more or less uniformly across the whole injection range (Fig.…”

Section: Effect Of Post-firing Illuminationsupporting

confidence: 82%

Thermal stability of silicon surface passivation by APCVD Al2O3

Black

Allen

Cuevas

et al. 2014

Solar Energy Materials and Solar Cells

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a b s t r a c tWe investigate the thermal stability of silicon surface passivation provided by aluminium oxide (Al 2 O 3 ) films deposited using atmospheric pressure chemical vapour deposition (APCVD) and fired in a belt furnace at a peak temperature of $ 810 1C. Firing stability is investigated for p-and n-type substrates as a function of Al 2 O 3 film thickness both with and without a plasma-enhanced chemical vapour deposition (PECVD) SiN x capping layer, and for boron-diffused surfaces with a $ 10 nm Al 2 O 3 film only. Excellent thermal stability of the passivation is demonstrated, with effective carrier lifetimes in n-type silicon wafers remaining stable or even improving after firing, and lifetimes in p-type wafers initially degrading slightly but recovering to above their initial values following $ 10 min illumination by a halogen lamp at $ 20 mW/cm 2 . Film thickness appears to be unimportant to stability, as does the presence of the capping layer. Surface recombination velocities of less than 3 cm/s for 1.35 Ω cm p-type and less than 2 cm/s for 1.2 Ω cm n-type substrates are measured after firing and illumination. The passivation of boron-diffused surfaces is also shown to improve slightly following firing, with a post-firing saturation current density of 42 fA/cm 2 on a diffusion with a sheet resistance of 100 Ω/□ and surface dopant concentration of $ 1.3 Â 10 19 cm −3 . Capacitance-voltage (C-V) measurements show that short firing times result in an initial reduction of the interface defect density D it and a slight increase of the negative insulator fixed charge density Q f , while longer firing results in a substantial increase in both Q f and D it .

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“…3(a) and (c)]. This increase can be attributed to an effect called "light induced curing" [22], which appears on fired samples with this specific SiN-1 layer. The exact cause for this increase is not yet known, although its cause might be linked to hydrogen [22].…”

Section: (D) Featuring a Differently Deposited Sin X :H Compared Withmentioning

confidence: 96%

Influencing Light and Elevated Temperature Induced Degradation and Surface-Related Degradation Kinetics in Float-Zone Silicon by Varying the Initial Sample State

Hammann

Engelhardt

Sperber

et al. 2020

IEEE J. Photovoltaics

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Light and elevated temperature induced degradation (LeTID) kinetics in float-zone silicon are investigated by varying the initial sample state, composed of different base material, base doping, SiN x :H films, and subsequent firing, and/or annealing steps. The approach of deliberately changing the initial sample state is shown to allow for specific studies of influences of LeTID kinetics. Bulk-and surface-related degradations are examined separately and the influence on the kinetics of bulk-and surface-related degradation is illustrated by a four-state and three-state model, respectively. In case of bulk-related degradation, an increase in defect density because of the firing step is shown, whereas the annealing step has an inverse effect. Both temperature stepsindividually and combined-influence the transition rates of bulkrelated degradation and regeneration by presumably changing the distribution of a defect precursor. For surface-related degradation, the firing step reduces the transition rate from the initial to the degraded state. In addition, the influence of a comparably humid atmosphere and the absence of UV light are found to be negligible. Index Terms-Bulk-related degradation (BRD), crystalline silicon, defect density, float zone (FZ), light and elevated temperature induced degradation (LeTID), surface-related degradation (SRD). I. INTRODUCTION L IGHT and elevated temperature induced degradation (LeTID) is a degradation phenomenon first found especially in mc-Si in 2012 [1]. Recently, a similar or the same phenomenon was discovered in Cz-Si [2], [3] and float-zone (FZ) Si [4], [5]. Compared with other degradation effects like boron-oxygen-related (BO) degradation [6], higher treatment temperatures >50°C are needed to investigate the effect on experimentally viable time scales [1], [7]. Besides LeTID, which is a bulk-related degradation (BRD), a second degradation phenomenon is visible and can be identified as a This work was supported by the German Federal Ministry for Economic Affairs and Energy under Contracts 0324226A and 0324001.

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Light Induced Curing (LIC) of Passivation Layers Deposited on Native Silicon Oxide

Cited by 11 publications

References 7 publications

New Perspectives on Surface Passivation: Understanding the Si-Al2O3 Interface

New Perspectives on Surface Passivation: Understanding the Si-Al2O3 Interface

Thermal stability of silicon surface passivation by APCVD Al2O3

Influencing Light and Elevated Temperature Induced Degradation and Surface-Related Degradation Kinetics in Float-Zone Silicon by Varying the Initial Sample State

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