Hopping charge transport in hydrogenated amorphous silicon-germanium alloy thin films

L. Stolik, Mohammadali Eslamisaray, E. Nguyen, U. R. Kortshagen, J. Kakalios

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Measurements of the dark conductivity and thermoelectric power in hydrogenated amorphous silicon-germanium alloys (a-Si1-xGex:H) reveal that charge transport is not well described by an Arrhenius expression. For alloys with concentrations of Ge below 20%, anomalous hopping conductivity is observed with a power-law exponent of 3/4, while the temperature dependence of the conductivity of alloys with higher Ge concentrations is best fit by a combination of anomalous hopping and a power-law temperature dependence. The latter has been attributed to charge transport via multi-phonon hopping. Corresponding measurements of the Seebeck coefficient reveal that the thermopower is n-type for the purely a-Si:H and a-Ge:H samples but that it exhibits a transition from negative to positive values as a function of the Ge content and temperature. These findings are interpreted in terms of conduction via hopping through either exponential band tail states or dangling bond defects, suggesting that the concept of a mobility edge, accepted for over five decades, may not be necessary to account for charge transport in amorphous semiconductors.

Original languageEnglish (US)
Article number225110
JournalJournal of Applied Physics
Issue number22
StatePublished - Jun 14 2022

Bibliographical note

Funding Information:
We gratefully acknowledge helpful discussions with David Drabold and Boris Shklovskii. This work was supported by NSF Grant No. DMR1608937, the Minnesota Environment and Natural Resources Trust Fund (ML 2016, Chap. 186, Sec. 2, Subdivision 07b), and the University of Minnesota. Parts of this work were carried out in the Characterization Facility, University of Minnesota, which receives partial support from the NSF through the MRSEC (Award No. DMR-2011401) and the NNCI (Award No. ECCS-2025124) programs. Portions of this work were conducted in the Minnesota Nano Center, which is supported by the National Science Foundation through the National Nano Coordinated Infrastructure Network (NNCI) under Award No. ECCS-1542202.

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