The Relation Between Microstructure and Electronic Properties of Magnetron Sputtered a-Si 1-x ,C x :H
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THE RELATION BETWEEN MICROSTRUCTURE AND ELECTRONIC PROPERTIES OF MAGNETRON SPUTTERED a-Sil-x,Cx:H
S.-Y. Yang, N. Maley * and J. R. Abelson Coordinated Science Laboratory and the Materials Science and Engineering Department, University of Illinois, Urbana, IL 61801; * present address: Solarex Corp., Thin Film Division, Newtown, PA 16802 Abstract We have grown a-Sil-x,Cx:H films by reactive magnetron sputtering, varying the H2
partial pressure from 0 to 6 mTorr and maintaining the substrate temperature at 275"C and argon and methane partial pressures at 1.70 and 0.10 mTorr, respectively. We investigate the correlation between electronic properties and the fraction of H bonded in
"microstructure," defined by the ratio of SiHx stretching mode absorptions in IR and the low temperature H2 release in thermal evolution. Our results on sputtered films disprove the monotonic decrease in carrier transport with increasing microstructure fraction which is commonly observed for a-SilxCx:H grown by glow discharge of SiH 4 and CH4 . We find that the electronic properties and microstructure depend on film composition and growth technique, and that the electronic
properties are not uniquely determined by the microstructure of hydrogen bonding. 1. Introduction Hydrogenated amorphous silicon carbon alloy (a-Sil-x,Cx:H) films play an important role in a wide variety of thin film devices including solar cells, thin-film transistors, photoreceptors,
x-ray sensors and color sensors.( 1 ) These applications utilize the wide, controllable energy gap obtained by varying the alloy compositional ratio. However, the electronic transport properties tend to worsen as the bandgap is increased. Efforts have been made to relate the microstructure and electronic properties of a-Sil-x,Cx:H .(2,3,4) A key aspect of microstructure is the H bonding, which has been studied by infra-red absorption and hydrogen thermal evolution for films deposited by various techniques. From infra-red absorption measurements, Bhattacharya and Mahan( 5) defined a microstructure fraction R (0
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