Doping effects of aluminium on the properties of hydrogenated amorphous silicon–carbon alloy films prepared by magnetron sputtering

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Abstract
Aluminium has been introduced into hydrogenated amorphous silicon-carbon alloy films prepared by reactive magnetron sputtering, using composite targets of silicon and aluminium in a methane-argon gas mixture. The doping effects of aluminium on the structural, optical, electrical and optoelectronic properties of the films were investigated. The ratio of silicon to carbon depended on the fractional aluminium content z The concentration of hydrogen bonded to silicon or carbon tended to decrease in the large-z range. These results are interpreted in terms of a gradual change in deposition process. From a thermoelectric power experiment, the type of conduction was found to change from n to p in the range of z< 1 × 10−2. Around z=1 × 10−2, the activation energy of the dark conductivity changed without changing the optical bandgap. These results indicate that doping is effective in this range of z In the large-z range, the films exhibit alloying behaviour as shown by a decrease in the optical bandgap, an increase in the dark conductivity and a quenching of photoconductivity effect.