Electrical properties of purified solar grade silicon substrates using a combination of porous silicon and SiCl4

This work investigates the photo-thermal treatment of solar grade (SG) silicon to reduce impurities to a low level suitable for high efficiency low-cost solar cells application. It describes experiment carried out by using a tungsten lamps furnace (rapid thermal processing, RTP) to purify solar grade silicon wafers using a combination of porous silicon (PS) and silicon tetrachloride. This process enables to attract the impurities towards the porous layer where they react with SiCl4 to form metallic chlorides. The gettering effect was studied using the Hall Effect and the Van Der Pauw methods to measure the resistivity, the majority carrier concentration and mobility. We have obtained a significant improvement of the majority carrier mobility after such thermo-chemical treatment. The gettering efficiency is also evaluated by the relative increase of the minority carrier diffusion length L, measured by the light beam induced current (LBIC) technique.