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Signature of the Weak Bond-Dangling Bond Conversion Process in a-Si:H as Seen by Total Photoelectron Yield Spectroscopy

Published online by Cambridge University Press:  01 January 1993

W. Graf ,
K. Leihkamm ,
J. Ristein  and
L. Ley
W. Graf
Affiliation:
Universität Erlangen-Nümberg,Institut für Technische Physik, Erwin-Rommel-Str. 1,, D-W-8520 Erlangen,, Germany
K. Leihkamm
Affiliation:
Universität Erlangen-Nümberg,Institut für Technische Physik, Erwin-Rommel-Str. 1,, D-W-8520 Erlangen,, Germany
J. Ristein
Affiliation:
Universität Erlangen-Nümberg,Institut für Technische Physik, Erwin-Rommel-Str. 1,, D-W-8520 Erlangen,, Germany
L. Ley
Affiliation:
Universität Erlangen-Nümberg,Institut für Technische Physik, Erwin-Rommel-Str. 1,, D-W-8520 Erlangen,, Germany
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Abstract

Photoelectron Yield Spectroscopy is one of the most direct methods to study the density of gap states of amorphous semiconductors. We have made use of it to investigate the transient changes of the density of gap states of a-Si:H upon illumination with above-band-gap light. An excitation density of 50 mW/cm2 of 532 nm light from a frequency doubled Nd-YAG laser was modulated with frequencies between 0.1 Hz and 10 KHz and the transient response of the photoelectron yield signal was monitored by gated electron counting or a lock-in amplifier. From this we deduce a reversible increase of the occupied density of defect states under illumination with a maximum Δg ∼ 1017 cm3 eV-1 at about 0.3 eV below the Fermi energy and a decrease below EF− 0.75 eV, i. e. in the region of deep tail states. The effect exhibits a wide spectrum of time constants involved. Based on additional transient surface photo voltage measurements as well as numerical simulations we argue that the observed redistribution of states is not due to a light induced change in surface band bending or due to a mere excitation of electrons from occupied to empty states. Instead, we interpret the observed effect as a conversion of weak to dangling bonds, i.e. a precursor of the Staebler-Wronski Effect, lacking however the final step of hydrogen stabilisation necessary for the creation of metastable defects.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 297: Symposium A – Amorphous Silicon Technology - 1993 , 1993 , 207
Copyright
Copyright © Materials Research Society 1993

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References

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