CONTROL OF MICROSTRUCTURE AND OPTOELECTRONIC PROPERTIES OF SI-H FILMSBY ARGON DILUTION IN PLASMA-ENHANCED CHEMICAL-VAPOR-DEPOSITION FROM SILANE

Structural and optoelectronic properties of thin films of silicon-hydr ogen binary alloy (Si:H) deposited from silane and argon mixture in a rf glow discharge plasma have been studied for different argon dilutio ns and rf powers. It has been observed that with low rf power density (30-10 mW/cm(3)) increase of argon dilution up to 95% reduces the micr ostructure in the films, as determined from IR absorption spectra. Sim ultaneously, increase in refractive index and decrease in ESR spin den sity have been observed. Above 95% argon dilution or with higher rf po wers, transmission electron microscopy (TEM) studies reveal a dominanc e of the columnar growth mechanism, and the optoelectronic properties of the films deteriorate. At 99% argon dilution, microcrystallites app ear to form within columnar regions. Addition of a small amount of hyd rogen to the silane-argon plasma improves the network significantly, w hich is manifested by the changes in the dark conductivities in the di fferent rf power regimes.