Reduction in a-Si:H density utilizing a secondary plasma

Abstract

Following the need to improve packaging and contact layers for photovoltaics and other optoelectronic applications, a renewed interest in the fabrication of thin, low-density silicon films has arisen. We demonstrate a reactive sputtering technique utilizing a secondary plasma to crack hydrogen gas during physical vapor deposition of silicon layers. Cracking efficiency of the gas varies heavily with pressure and power from under 10% to nearly 100% conversion to hydrogen radicals. Radicals incorporated into the film produce amorphous silicon films with densities as low as 1.73 g / cm3, compared to 2.2 g / cm3 in their nonhydrogenated counterparts. Reduced density films likewise have a reduction in index of refraction comparable to other hydrogenated amorphous silicon produced by other techniques with indices close to 2 across the visible portion of the spectrum. Our work represents a useful, scalable advance in the production of amorphous hydrogenated silicon for a variety of applications requiring large areas.