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AC Theory of Constant Photocurrent Measurement

Published online by Cambridge University Press:  15 February 2011

G. Conte ,
A. Eray ,
G. Nobile  and
F. Palma
G. Conte
Affiliation:
ENEA, Centro Ricerche Fotovoltaiche, Loc. Granatello, P.O.B. 32, 80055 Portici (NA), Italy
A. Eray
Affiliation:
Hacettepe University, Department of Physics Engineering, Ankara, Turkiye
G. Nobile
Affiliation:
ENEA, Centro Ricerche Fotovoltaiche, Loc. Granatello, P.O.B. 32, 80055 Portici (NA), Italy
F. Palma
Affiliation:
Dip. di Ingegneria Elettronica, UniversitÀ ‘La Sapienza’, Roma, Italy
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Abstract

In this paper we present a study of ac the Constant Photocurrent Measurement (CPM) with the aim to assess the precision of this method compared to the de CPM. In particular, we introduce a small signal theory of the ac photoconductivity, we relate the sub-bandgap absorption to the density of defects, and we assume a combination of a constant plus a sinusoidal generation rate. The method allows to calculate the variation occurring in defect occupation as a function of the wavelength and intensity of the light, and of the ac test frequency. We show that, in ac condition, carriers lifetime is a complicated function of the chosen parameter, and it is affected by the delay due to charge accumulation of free and trapped carrier densities. Large influence on the lifetime is played not only by recombination, which takes place all along the gap defects included between the two quasi-Fermi levels, but also by the process of carrier trapping and emission by defects located close to the quasi-Fermi levels. Both processes introduce large phase delay. Further information can thus be obtained from CPM by evaluating the phase behavior. Our analysis leads to a new method of evaluation of the dangling bond capture cross section and of their charged-to-neutral capture cross section ratio.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 377: Symposium A – Amorphous Silicon Technology 1995 , 1995 , 509
Copyright
Copyright © Materials Research Society 1995

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References

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