Recombination at dangling bonds and steady-state photoconductivity in<i>a</i>-Si:H

Vaillant, F.; Jousse, D.

doi:10.1103/physrevb.34.4088

Cited by 93 publications

(32 citation statements)

References 34 publications

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“…In this work, we extend the model previously established ͑but not widely spread͒ for bulk a-Si:H recombination 10,11 to the description of the surface recombination through dangling bonds. For a better understanding of our approach, the relevant underlying hypotheses and properties of this recombination model are summarized below.…”

Section: Dangling Bond Interface Recombination Modelmentioning

confidence: 96%

Model for a-Si:H/c-Si interface recombination based on the amphoteric nature of silicon dangling bonds

2007

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The performance of many silicon devices is limited by electronic recombination losses at the crystalline silicon ͑c-Si͒ surface. A proper surface passivation scheme is needed to allow minimizing these losses. The surface passivation properties of amorphous hydrogenated silicon ͑a-Si:H͒ on monocrystalline Si wafers are investigated here. We introduce a simple model for the description of the surface recombination mechanism based on recombination through amphoteric defects, i.e. dangling bonds, already established for bulk a-Si:H. In this model, the injection-dependent recombination at the a-Si:H/c-Si interface is governed by the density and the average state of charge of the amphoteric recombination centers. We show that with our surface recombination model, we can discriminate between the respective contribution of the two main mechanisms leading to improved surface passivation, which is achieved by ͑a͒ the minimization of the density of recombination centers and ͑b͒ the strong reduction of the density of one carrier type near the interface by field effect. We can thereafter reproduce the behaviors experimentally observed for the dependence of the surface recombination on the injection level on different wafers, i.e., of both p and n doping type as well as intrinsic. Finally, we are able to exploit the good surface passivation properties of our a-Si:H layers by fabricating flat heterojunction solar cells with open-circuit voltages exceeding 700 mV.

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Section: Dangling Bond Interface Recombination Modelmentioning

confidence: 96%

Model for a-Si:H/c-Si interface recombination based on the amphoteric nature of silicon dangling bonds

2007

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“…20 In the present case, the assumption is made that the interface recombination is occurring through amphoteric defects. 21 In the current formalism, the two model parameters are the dangling bond surface density N DB S and the charge density at the interface Q S . Electronically, the amphoteric defects ͑i.e., dangling bonds͒ are characterized by their electron and hole capture cross sections, respectively in the neutral states n 0 and p 0 and the charged states n + and p − .…”

mentioning

confidence: 99%

Stretched-exponential a-Si:H∕c-Si interface recombination decay

Wolf¹,

Olibet²,

Ballif³

2008

Applied Physics Letters

134

113

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The electronic properties of hydrogenated amorphous silicon ͑a-Si: H͒ relax following stretched exponentials. This phenomenon was explained in the past by dispersive hydrogen diffusion, or by retrapping included hydrogen motion. In this letter, the authors report that the electronic passivation properties of intrinsic a-Si: H/crystalline silicon ͑c-Si͒ interfaces relax following a similar law. Carrier injection dependent a-Si: H / c-Si interface recombination calculations suggest this originates from amphoteric interface state ͑or Si dangling bond͒ reduction, rather than from a field effect. These findings underline the similarity between a-Si: 3 Alternatively, c-Si surface dangling bond passivation may also be obtained by deposition of intrinsic hydrogenated amorphous silicon ͑a-Si: H͒ films. 4 As such films can, in addition, be doped relatively easily, they allow for the fabrication of electronically abrupt a-Si: H / c-Si heterojunctions.5 Since direct deposition of such doped films on c-Si can result in poor interface properties, typically, a few nanometer thin intrinisic a-Si: H͑i͒ buffer layer is inserted in between for a-Si: H / c-Si heterostructure solar cell fabrication.6 Impressive large area ͑Ͼ100 cm 2 ͒ energy conversion efficiencies ͑Ͼ22% ͒ have been reported for such devices.7 For this, atomically sharp a-Si: H / c-Si interfaces, i.e., where no epitaxial Si ͑epi-Si͒ film was grown on the wafer during film deposition, are considered to be essential. 8 This can be monitored in real time by various optical probes.9,10 On a related note, the excellent a-Si: H / c-Si interface passivation properties may also offer an explanation why surrounding a-Si: H tissue is crucial for device-grade microcrystalline Si.11 Nevertheless, the relation between processing parameters and the physical mechanism underlying the a-Si: H / c-Si interface passivation is not yet fully understood.Previously it was suggested that low-temperature annealing is beneficial for the interface passivation quality, provided that neither epi-Si at the interface 12 nor boron-doped overlayer 13,14 is present. In this letter, we show that under these conditions electronic passivation relaxation can be accurately described by stretched exponentials. It is observed that even moderate temperature ͑ഛ 180°C͒ annealing can yield an extremely low interface recombination activity. Carrier injection dependent recombination calculations suggest that the origin of this phenomenon is related to dangling bond reduction at the interface, rather than to a field effect.Consequently, similar to the SiO 2 / c-Si interface, 15 also here, a strong analogy between the nature of the defects present at the a-Si: H͑i͒ / c-Si interface and those in the a-Si: H͑i͒ bulk may possibly exist.For the experiments, 300 m thick ϳ3.0 ⍀ cm phosphorus-doped high quality float zone ͑100͒ FZ-Si wafers were used. Both substrate surfaces were mirror polished to eliminate the influence of substrate surface roughness on the passivation properties. 16 Surface cleaning simply consisted o...

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“…[6]. This approach is valid provided steady-state conditions and non-interacting neighbouring defect states.…”

Section: Recombination Statisticsmentioning

confidence: 92%

“…Since thermal re-emission is only negligible for energy levels between a pair of Quasi-Fermi-Levels (QFLs) for traps, the error of the scf can be estimated by comparing D it (E) to the positions of the QFLs [5]. In this paper, we implement the full model for amphoteric recombination statistics [6], abbreviated as ncf (non-closed-form). D it is modeled based on the Defect-Pool-Model (DPM) for threedimensional materials [7,8], adapted to interfaces by fitting to measurements [3].…”

mentioning

confidence: 99%

Comprehensive model for interface recombination at a‐Si:H/c‐Si interfaces based on amphoteric defects

Steingrube

Brendel

et al. 2010

Phys. Status Solidi (c)

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Today, most fabricated solar cells are made of crystalline Silicon (c‐Si) wafers. Electronic passivation of defect states at interfaces is a major issue in recent cell development. A current topic is surface passivation using hydrogenated amorphous Silicon (a‐Si:H). The purpose of this paper is to describe recombination at the a‐Si:H/c‐Si interface by a comprehensive model considering recombination via amphoteric defects. The density of defect states at the interface (Dit) is modeled via the Defect‐Pool‐Model(DPM), adapted to a‐Si:H/c‐Si interfaces by fitting to published experimental data. Since our model accounts for the amphoteric nature of defects at the hetero‐interface, and approximates Dit by a physical model, parameters are physical more meaningful and allow for an investigation of measured recombination properties. A numerical comparison between different recombination models shows that using amphoteric recombination statistics is more generally applicable. The purpose is to apply the model in numerical semiconductor device simulators for accurate modeling of a‐Si:H passivated c‐Si solar cells. Limitations of cell performance due to interface recombination can then be traced back to physical parameters which helps to optimize cell designs (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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Recombination at dangling bonds and steady-state photoconductivity ina-Si:H

Cited by 93 publications

References 34 publications

Model for a-Si:H/c-Si interface recombination based on the amphoteric nature of silicon dangling bonds

Model for a-Si:H/c-Si interface recombination based on the amphoteric nature of silicon dangling bonds

Stretched-exponential a-Si:H∕c-Si interface recombination decay

Comprehensive model for interface recombination at a‐Si:H/c‐Si interfaces based on amphoteric defects

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