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Electron emission from deep traps in hydrogenated amorphous silicon and silicon-germanium: Meyer-Neldel behavior and ionization entropy

Published online by Cambridge University Press:  02 August 2011

Qi Long ,
Steluta Dinca ,
Eric A. Schiff ,
Baojie Yan ,
Jeff Yang  and
Subhendu Guha
Qi Long
Affiliation:
Department of Physics, Syracuse University, Syracuse, New York 13244-1130, U.S.A.
Steluta Dinca
Affiliation:
Department of Physics, Syracuse University, Syracuse, New York 13244-1130, U.S.A.
Eric A. Schiff
Affiliation:
Department of Physics, Syracuse University, Syracuse, New York 13244-1130, U.S.A.
Baojie Yan
Affiliation:
United Solar Ovonic LLC, Troy, Michigan 48084, U.S.A.
Jeff Yang
Affiliation:
United Solar Ovonic LLC, Troy, Michigan 48084, U.S.A.
Subhendu Guha
Affiliation:
United Solar Ovonic LLC, Troy, Michigan 48084, U.S.A.
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Abstract

We have measured electron drift in amorphous silicon-germanium nip photodiodes using the photocarrier time-of-flight technique. The samples show electron deep-trapping shortly after photogeneration, which is generally attributed to capture by a neutral dangling bond (D0) to form a negatively charged center (D-). An unusual feature is that electron re-emission from the trap is also clearly seen in the transients. Temperature-dependent measurements on the emission yield an activation energy of about 0.8 eV and the remarkably large value of 1015 Hz for the emission prefactor frequency. We also compiled results on electron emission from deep traps in a-Si:H, a-SiGe:H, and a-SiC:H from six previous publications. Collectively, these measurements exhibit "Meyer Neldel" behavior for electron emission over a range of activation energies from 0.2–0.8 eV and a prefactor range extending over nine decades, from 106 to 1015 Hz. The Meyer-Neldel behavior is consistent with the predictions of the multi-excitation entropy model. We extract a ionization entropy of 20kB from the measurements, which is very large compared to crystal silicon. We discuss this result in terms of a bond charge model.

Keywords

defectsSiamorphous
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1321: Symposium A – Amorphous and Polycrystalline Thin-Film Silicon Science and Technology , 2011 , mrss11-1321-a04-04
Copyright
Copyright © Materials Research Society 2011

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