Signature of the weak bond-dangling bond conversion process in a-Si:H as seen by total photoelectron yield spectroscopy

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Details zur Publikation

Autorinnen und Autoren: Ristein J, Ley L
Titel Sammelwerk: Materials Research Society Symposium Proceedings
Verlag: Materials Research Society
Jahr der Veröffentlichung: 1993
Band: 297
Tagungsband: MRS Proceedings
Seitenbereich: 207
ISSN: 0272-9172


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 to approximately 1017 cm-3 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 stabilization necessary for the creation of metastable defects.

FAU-Autorinnen und Autoren / FAU-Herausgeberinnen und Herausgeber

Ley, Lothar Prof. Dr.
Naturwissenschaftliche Fakultät
Ristein, Jürgen apl. Prof. Dr.
Lehrstuhl für Laserphysik

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