Study on contact materials for sulfur hyperdoped Black Silicon

Irradiating a plane silicon surface with a train of intense femtosecond-laser pulses in a sulfur-containing atmosphere leads to a structured surface with enhanced absorption properties in the visible and near infrared spectral range, even at wavelengths below the band gap. The ensuing Black Silicon is a prospective candidate for intermediate band photovoltaics and additionally internalizes light trapping properties. Because the resulting layer system shows photovoltaic activity, it is proposed to turn this absorption into an efficient charge carrier generation for photovoltaic applications. Extracting those charge carriers is difficult, because of a structured, nanocrystalline surface layer with a thickness of d <;1μm and a sulfur content of about 1 at. % which influences the mechanical adhesion and contact resistances. Deposition techniques like screen printing, sputtering, pulsed laser deposition and thermal evaporation are compared. We use different metal layer systems like silver, titanium/palladium/silver, chromium/gold and transparent contacts made from aluminum doped zinc oxide. We evaluate the contact behavior by means of impedance spectroscopy finding the appropriate contact material for devices.