Bandtails and defects in microcrystalline silicon (μc-Si:H)

Fuhs, W.; Kanschat, P.; Lips, K.

doi:10.1116/1.591473

Cited by 28 publications

(21 citation statements)

References 16 publications

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“…12 However, others have attributed the LESR signal to electrons trapped in the localized, conduction-band-tail states. [23][24][25] This attribution is supported by a study of the photoconductivity and the density of LESR states as functions of the generation rate. 24,25 These results can only be explained by means of localized carriers.…”

Section: -13mentioning

confidence: 88%

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ESR observations of paramagnetic centers in intrinsic hydrogenated microcrystalline silicon

et al. 2002

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Paramagnetic centers in hydrogenated microcrystalline silicon, c-Si:H have been studied using dark and light-induced electron-spin resonance ͑ESR͒. In dark ESR measurements only one center is observed. The g values obtained empirically from powder-pattern line-shape simulations are g ʈ ϭ2.0096 and g Ќ ϭ2.0031. We suggest that this center may be due to defects in the crystalline phase. During illumination at low temperatures, an additional ESR signal appears. This signal is best described by two powder patterns indicating the presence of two centers. One center is asymmetric (g ʈ ϭ1.999, g Ќ ϭ1.996), while the other is characterized by large, unresolved broadening such that unique g values cannot be obtained. The average g value for this center is 1.998. The light-induced signal, which we interpret as coming from carriers trapped in the band tails at the crystalline grain boundaries, remains for at least several minutes after the light is turned off. Although the time scales of the decay curves are very different for two samples prepared by different techniques, both decays can be fitted using the assumption of recombination due to distant pairs of electrons and holes trapped in localized band-tail states.

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Section: -13mentioning

confidence: 88%

“…[23][24][25] This attribution is supported by a study of the photoconductivity and the density of LESR states as functions of the generation rate. 24,25 These results can only be explained by means of localized carriers. Moreover, the asymmetric line shape is not consistent with free electrons in the conduction band.…”

Section: -13mentioning

confidence: 92%

ESR observations of paramagnetic centers in intrinsic hydrogenated microcrystalline silicon

et al. 2002

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“…The assumption of these features is justified by various results in the literature. [17][18][19] We thus assume a mobility band gap with exponential band tails at the band edges and defects located between the band edges with distributions that can be described by Gaussians. We use a band gap value of 1.2 eV to describe both the intrinsic and doped nc-Si:H and vary the mobilities in a wide range to study their effect on PG, and later we fix the electron and hole mobilities to be 40 cm 2 / Vs and 4 cm 2 / Vs, respectively, for intrinsic ncSi:H. Properties of the doped layers and of the ITO and ZnO layers were also assumed to be homogeneous.…”

Section: Simulation Results: Sensitivity Studymentioning

confidence: 99%

Photogating effect as a defect probe in hydrogenated nanocrystalline silicon solar cells

Schropp¹,

Rubinelli²

2010

Journal of Applied Physics

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The measurement of the spectrally resolved collection efficiency is of great importance in solar cell characterization. Under standard conditions the bias light is a solar simulator or a light source with a similar broadband irradiation spectrum. When a colored blue or red bias light is used instead, an enhanced collection efficiency effect, in the literature known as the photogating effect, can be observed under certain conditions. While most of the published reports on such effect were on solar cells with amorphous silicon based absorber layers, we have shown that the enhanced collection efficiency could be also present in thin film silicon solar cells where hydrogenated nanocrystalline silicon ͑nc-Si:H͒ is used as the absorber layer. In this article we present detailed experimental results and simulations aiming at a better understanding of this phenomenon. We show that the collection efficiency is strongly dependent on the intensity of bias light and the intensity of the monochromatic light. These experimental results are consistent with the computer predictions made by our code. We also show that the photogating effect is greatly enhanced when nanocrystalline silicon cells are built with an improperly doped p-layer or with a defective p/i interface region due to the reduced internal electric field present in such cells. The existence of this effect further proves that carrier transport in a nc-Si:H solar cell with an i-layer made close to the phase transition regime is influenced to a large extent by drift transport. The study of this effect is proposed as an alternative approach to gain a deeper understanding about the carrier transport scenarios in thin film solar cells, especially nanocrystalline silicon solar cells.

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“…exposed to a quasi-continuous microwave radiation and resonant changes of the sample current detected with standard lock-in techniques are indicative of the electronic activity of a defect. As shown in figure 2, EDMR revealed that tunnelling between shallow tail states of the conduction band (CE, Landé factor g = 1.998) and neutral dangling bonds (db 0 , g ≈ 2.005) exists in undoped µc-Si:H at T = 5K [12]. At higher T , the CE line disappears and the single db line remains.…”

Section: Introductionmentioning

confidence: 92%

A pulsed EDMR study of hydrogenated microcrystalline silicon at low temperatures

Boehme

Lips

2004

phys. stat. sol. (c)

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Experimental results of pulsed electrically detected magnetic resonance (pulsed EDMR) measurements are reviewed with regard to the question for microscopic mechanisms that determine the lifetimes of excess charge carriers in hydrogenated microcrystalline silicon. The results show that two qualitatively different dangling bond (db) recombination processes occur. (i) Distant pair recombination through shallow conduction band tail states (CE centers) and dbs and (ii) a db direct capture (dc) recombination where charge carriers localize directly at dbs. For the db-dc process, it is shown that an intermediate, excited triplet state of the db exists which lies about 50meV below the conduction band edge. The recombination probabilities of this path are quantified by means of pulsed EDMR. The temperature and light intensity dependencies suggest that under the experimental conditions given, the db-dc process is not only electronically more active in comparison to the CE-db process, it is even the determining process for the lifetime of excess charge carriers.

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Bandtails and defects in microcrystalline silicon (μc-Si:H)

Cited by 28 publications

References 16 publications

ESR observations of paramagnetic centers in intrinsic hydrogenated microcrystalline silicon

ESR observations of paramagnetic centers in intrinsic hydrogenated microcrystalline silicon

Photogating effect as a defect probe in hydrogenated nanocrystalline silicon solar cells

A pulsed EDMR study of hydrogenated microcrystalline silicon at low temperatures

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