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Proceedings Paper

Effects Of Deposition Conditions On The Conductivity And Photoconductivity Of rf Sputtered a-Ge:H and a-Gel_xCx:H
Author(s): J. Shinar; H.-S. Wu
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Paper Abstract

a-Ge:H and a-Ge1_xCx:H films were prepared by rf sputtering of 4 polycrystalline Ge target in a background vacuum ~4x10-7 at rf power 5O<P<600W (0.27-3.3W/cm2), target-to-substrate distances 1≤d≤7", varying partial pressures of Ar, H2, and propane, and flow rates f. The dark conductivity σd and photoconductivity σph increase with increasing d up to 6", apparently due to thermalization of the ions and Ge atoms bombarding the growing film. σd and σph also increase at f<lsccm, due to the incorporation of oxygen and other impurities from the background residual atmosphere. At the optimal values of f and d, σph and ad increase with P. Although all increases in aph are significant relative to those bf previously reported rf sputtered a-Ge:H, the values arb still much lower than those of glow discharge deposited films, which are in turn lower than those of rf magnetron sputtered films grown in high vacuum (<5x10-9 torr). The similar behavior of σd and σph, the relatively long lifetimes of the carriers ι - 0.8ms but very low mobility μ 5x10-7 cm4/Vsec and low subgap absorption suggest that the transport is dominated by defects near the mobility edge. The failure of a biased screen placed above the substrate to affect σph suggests that the high values of aph reported using rf magnetron sputtering are at least in part due to the improved background vacuum. Although incorporation of significant amounts of carbon sharply reduces σph, a small content, sufficient to increase the optical gap to 1.3-1.4eV, has little effect on σph.

Paper Details

Date Published: 6 March 1989
PDF: 8 pages
Proc. SPIE 1016, Optical Materials Technology for Energy Efficiency and Solar Energy Conversion VII, (6 March 1989); doi: 10.1117/12.949919
Show Author Affiliations
J. Shinar, Iowa State University (United States)
H.-S. Wu, Iowa State University (United States)

Published in SPIE Proceedings Vol. 1016:
Optical Materials Technology for Energy Efficiency and Solar Energy Conversion VII
Claes-Goeran Granqvist; Carl M. Lampert, Editor(s)

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