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Analysis of the Conduction Properties of a-Si:H n+-i-n+ Structures Via Accurate Computer Modelling

Published online by Cambridge University Press:  10 February 2011

P. Chatterjee ,
R. Vanderhaghen  and
B. Equer
P. Chatterjee
Affiliation:
Energy Research Unit, Indian Association for the Cultivation of Science, Calcutta 700032, INDIA
R. Vanderhaghen
Affiliation:
Laboratoire de Physique des Interfaces et des Couches Minces, Ecole Polytechnique, F-91128 PALAISEAU Cedex, FRANCE.
B. Equer
Affiliation:
Laboratoire de Physique des Interfaces et des Couches Minces, Ecole Polytechnique, F-91128 PALAISEAU Cedex, FRANCE.
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Abstract

Analysis of the current density-voltage (J-V) characteristics of sandwich a-Si:H n+-i-n+ structures made of the same materials but with varying thicknesses of the i-layer, has given rise to two somewhat contradictory speculations regarding the density of states (DOS) at the Fermi level of the i-layer. The first of these postulates that the DOS over the first 2000–4000A of the i-a-Si:H layer is larger by a factor of 3–10 than that in the rest of the film With this hypothesis however, the experimentally observed low activation energies (Ea) for thin n+-i-n+ devices remain unexplained. In the other analysis, a consideration of the n+-i space-charge regions enables a fair description of the experimental results assuming that the electron DOS is position independent in the i-layer. In the present report we use accurate computer modelling to calculate and analyse the J-V characteristics of a-Si:H n+-i-n+ structures in the low bias ohmic region as a function of device thickness, ambient temperature and the quality of the i-layer. We find that the n+-i interface is abrupt only for a device with a high dangling bond density. For good quality material however, the depletion width extends right across the i-layer for a thin device and the zone of charge neutrality is never reached, resulting in low values of Ea in the ohmic region. In the latter case Ea increases with i-layer thickness. Analysis by detailed computer modelling confirms that the experimental results may be explained by assuming a density of states independent of the thickness of the i-layer.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 420: Symposium A – Amorphous Silicon Technology-1996 , 1996 , 233
Copyright
Copyright © Materials Research Society 1996

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