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Determination of a-Si:H Film Quality Throughfst and Sclc Techniques

Published online by Cambridge University Press:  25 February 2011

R. Martins ,
M. Vieira ,
E. Fortunato ,
I. Ferreira ,
F. Soares  and
L. GuimarĀes
R. Martins
Affiliation:
Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa/UNINOVA Quinta da Torre, 2825 — Monte da Caparica, PORTUGAL
M. Vieira
Affiliation:
Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa/UNINOVA Quinta da Torre, 2825 — Monte da Caparica, PORTUGAL
E. Fortunato
Affiliation:
Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa/UNINOVA Quinta da Torre, 2825 — Monte da Caparica, PORTUGAL
I. Ferreira
Affiliation:
Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa/UNINOVA Quinta da Torre, 2825 — Monte da Caparica, PORTUGAL
F. Soares
Affiliation:
Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa/UNINOVA Quinta da Torre, 2825 — Monte da Caparica, PORTUGAL
L. GuimarĀes
Affiliation:
Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa/UNINOVA Quinta da Torre, 2825 — Monte da Caparica, PORTUGAL
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Abstract

The ambipolar diffusion length (L*) and the effective lifetime (τ*) in undoped a-Si:H films have been measured by the Flying Spot Technique (FST). This technique consists in measuring the decay range of charges in Schottky barriers and the potential induced by a laser beam with a constant motion rate. The data show that the FST measurements are quite suitable to determine separately the effective diffusion length and the effective lifetime of the carriers, taking into account the surface effect. The results also indicate that the photosensitivity is not the best parameter to characterize film quality. Indeed, films with high photosensitivity can present a poor lifetime and diffusion length that make them unsuitable to be used in optoelectronic devices. The results obtained by FST have been correlated with the Density of States (DOS) inferred by the Space Charge Limited Current (SCLC) measurements performed in the temperature range of 300–430 K and by the Constant Photocurrent Method (CPM) in forward biased Schottky diodes at room temperature. The dependence of the DOS on temperature shows that the SCLC technique is clearly influenced by the thermally activated carriers.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 192: Symposium O – Amorphous Silicon Technology - 1990 , 1990 , 169
Copyright
Copyright © Materials Research Society 1990

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References

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