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On the Role of Charged Defect States and Deep Traps in the Photocarrier Drift and Diffusion in a-Si:H

Published online by Cambridge University Press:  17 March 2011

Paul Stradins
Affiliation:
Thin Film Silicon Solar Cells Super Laboratory, Electrotechnical Laboratory Tsukuba, Ibaraki 305-8568, Japan, emailstradins@etl.go.jp
Akihisa Matsuda
Affiliation:
Thin Film Silicon Solar Cells Super Laboratory, Electrotechnical Laboratory Tsukuba, Ibaraki 305-8568, Japan
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Abstract

The drift and diffusion in the presence of charged defects and photocarriers trapped in the tail states is re-examined. In continuity equations, diffusive and drift currents are related to free particles while the Poisson equation includes all charges. In order to make use of ambipolar diffusion approximation, the mobilities and diffusion coefficients should be attributed to the total electron and hole populations making them strongly particle-number dependent. Due to the asymmetry of the conduction and valence band tails, almost all trapped electrons reside in negatively charged defects (D). A simple model of photocarrier traffic via tail and defect states allows to establish the effective mobility values and coefficients in Einstein relations. In a photocarrier grating experiment, grating of D is counterbalanced by the grating of trapped holes. Nevertheless, electrons remain majority carriers, allowing the measurement of minority carrier diffusion length, but analysis is needed to relate the latter with μτ product.

Type
Research Article
Copyright
Copyright © Materials Research Society 2000

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References

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