Creation of metastable defects in a-Si:H by keV-electron irradiation at different temperatures

Diehl, Frank; Herbst, W.; Bauer, S.; Schröder, Bernd

doi:10.1016/0022-3093(95)00717-2

Cited by 20 publications

(16 citation statements)

References 7 publications

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“…With this result, the proposed relationship is now confirmed experimentally on a number of different samples over a much wider range than documented so far. To illustrate this, we compare our data ͑sample SC= 9%͒ with the data of earlier works 2,33,35,44,46 in Fig. 7͑b͒.…”

Section: A Conductivity In Intrinsic A-si: Hmentioning

confidence: 99%

Relationship between defect density and charge carrier transport in amorphous and microcrystalline silicon

et al. 2009

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The influence of dangling-bond defects and the position of the Fermi level on the charge carrier transport properties in undoped and phosphorous doped thin-film silicon with structure compositions all the way from highly crystalline to amorphous is investigated. The dangling-bond density is varied reproducibly over several orders of magnitude by electron bombardment and subsequent annealing. The defects are investigated by electron-spin-resonance and photoconductivity spectroscopies. Comparing intrinsic amorphous and microcrystalline silicon, it is found that the relationship between defect density and photoconductivity is different in both undoped materials, while a similar strong influence of the position of the Fermi level on photoconductivity via the charge carrier lifetime is found in the doped materials. The latter allows a quantitative determination of the value of the transport gap energy in microcrystalline silicon. The photoconductivity in intrinsic microcrystalline silicon is, on one hand, considerably less affected by the bombardment but, on the other hand, does not generally recover with annealing of the defects and is independent from the spin density which itself can be annealed back to the as-deposited level. For amorphous silicon and material prepared close to the crystalline growth regime, the results for nonequilibrium transport fit perfectly to a recombination model based on direct capture into neutral dangling bonds over a wide range of defect densities. For the heterogeneous microcrystalline silicon, this model fails completely. The application of photoconductivity spectroscopy in the constant photocurrent mode ͑CPM͒ is explored for the entire structure composition range over a wide variation in defect densities. For amorphous silicon previously reported linear correlation between the spin density and the subgap absorption is confirmed for defect densities below 10 18 cm −3 . Beyond this defect level, a sublinear relation is found i.e., not all spin-detected defects are also visible in the CPM spectra. Finally, the evaluation of CPM spectra in defect-rich microcrystalline silicon shows complete absence of any correlation between spindetected defects and subband gap absorption determined from CPM: a result which casts considerable doubt on the usefulness of this technique for the determination of defect densities in microcrystalline silicon. The result can be related to the inhomogeneous structure of microcrystalline silicon with its consequences on transport and recombination processes.

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Section: A Conductivity In Intrinsic A-si: Hmentioning

confidence: 99%

Relationship between defect density and charge carrier transport in amorphous and microcrystalline silicon

et al. 2009

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“…18,19 The electron beam current density during our experiments was 25 A cm Ϫ2 . A typical image required a 3 s exposure, and an entire series taken from one area required about 20 min, for a total dose of ϳ3ϫ10 4 Coulomb cm Ϫ2 .…”

Section: V(k) Is Given Bymentioning

confidence: 99%

“…However, the electron illumination is confined to a circular region about one micron in diameter, and the total beam current is 70 nA, yielding a total power of only 0.6 W. This shows that temperature changes associated with electron irradiation are negligible. Based on earlier published work, 18,19 an exposure of around 1 ms, at the electron dose we use, should be equivalent to our total light dose. If that were the case, e-beam effects should dominate the results, with no discernible contribution from the light soaking.…”

Section: V(k) Is Given Bymentioning

confidence: 99%

“…18,19 Previous ebeam irradiation experiments were performed in a scanning electron microscope, where an intense focused electron beam is scanned rapidly over very large areas; however the modeling assumed uniform illumination. It is known that there is a striking increase in the efficiency of Staebler-Wronski defect production with high-intensity pulsed light beams.…”

Section: V(k) Is Given Bymentioning

confidence: 99%

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Structural disorder induced in hydrogenated amorphous silicon by light soaking

Gibson

Treacy

Voyles

et al. 1998

Applied Physics Letters

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We show, using variable coherence transmission electron microscopy, that light soaking of amorphous hydrogenated silicon thin films leads to structural changes. We speculate that the structural changes are associated with instability in the as-deposited material. We suggest that improved immunity to Staebler-Wronski degradation could be achieved by a less-ordered material which is closer to the ideal continuous random network. © 1998 American Institute of Physics. ͓S0003-6951͑98͒02947-7͔The light-induced creation of dangling bond defects in hydrogenated amorphous silicon ͑a-Si:H͒, called the Staebler-Wronski effect ͑SWE͒, 1-3 has proven an obstacle to the widespread technological application of this material. Although the Staebler-Wronski effect saturates with the creation of about 10 17 /cm 3 , there is growing indirect evidence that a much larger number of atoms are affected by light soaking. [4][5][6] Here, we report that there is a significant structural change in hydrogenated amorphous silicon after light soaking, which we have observed using variable coherence electron microscopy. Our experiments show no such structural change in hydrogen-free silicon. In the light of our previous work on pure amorphous Ge and Si, 7,8 we interpret this result as evidence for a structural instability in the as-deposited a-Si:H structure, which has more medium-range order than the continuous random network. We propose that the Staebler-Wronski effect is intimately related to this structural instability.Electron fluctuation microscopy techniques have high sensitivity to such subtle structural changes. Diffraction, including small angle scattering, and other single-scattering techniques such as extended x-ray absorption fine structure ͑EXAFS͒ reveal correlations between pairs of atoms only, as embodied in the radial distribution function ͑RDF͒, which is not sensitive to subtle differences between network structures. 7 We have shown that higher-order atomic correlation functions ͑three and four body͒, which are measured by variable coherence microscopy, 9 are sensitive to such differences. 7 Specifically, variable coherence electron microscopy can detect correlations at a characteristic length scale of 10-20 Å that fall short of the perfect ordering necessary for strong diffraction. Raman scattering and x-ray absorption near-edge structure may also provide useful information about medium-range order, but the interpretation of these techniques is complicated by the need to know the internal properties of the atoms in order to calculate the vibrational spectrum or electronic density of states. Because variable coherence electron microscopy uses high energy electrons as a probe, the atoms' positions are their most important attribute, supplemented by the well-known atomic scattering factor.For this experiment amorphous hydrogenated silicon films of varied composition were deposited by reactive magnetron sputtering of a silicon target in argon and hydrogen. This method permits independent control of hydrogen content, and produces m...

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“…A very limited degradation of the performance was observed (in contrast to the ones of Fig. 4): At low light intensity roughly equivalent to T exposure, I sc was observed to decrease from 2.4 to 2.3 A/cm 2 while FF was reduced from 60 to 55% following the electron beam irradiation Beta irradiations a-Si:H diodes using SEM microscopes were already performed in the past by two different groups as mean to study defect creation [13,14]. These studies using 20 keV beams show that a significant increase of the defect densities occurs for deposited energy well above 0.1 J/cm 2 .…”

Section: Resultsmentioning

confidence: 96%

Amorphous silicon based betavoltaic devices

et al. 2013

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Hydrogenated amorphous silicon betavoltaic devices are studied both by simulation and experimentally. Devices exhibiting a power density of 0.1 W/cm 2 upon Tritium exposure were fabricated. However, a significant degradation of the performance is taking place, especially during the first hours of the exposure. The degradation behavior differs from sample to sample as well as from published results in the literature. Comparisons with degradation from beta particles suggest an effect of tritium rather than a creation of defects by beta particles.

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Creation of metastable defects in a-Si:H by keV-electron irradiation at different temperatures

Cited by 20 publications

References 7 publications

Relationship between defect density and charge carrier transport in amorphous and microcrystalline silicon

Relationship between defect density and charge carrier transport in amorphous and microcrystalline silicon

Structural disorder induced in hydrogenated amorphous silicon by light soaking

Amorphous silicon based betavoltaic devices

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