Search

Formation and separation of thin porous silicon films from the original substrate in combination with the transfer of such films onto a cheap foreign substrate for the photovoltaic application provides a straightforward way to cost reduction. Separation of the porous silicon film from the reusable p+ silicon substrate is achieved by electrochemical etching of silicon under specific HF concentration and current densities. The effect of HF concentration on film separation is studied. It is found that film separation is possible only for HF concentration of 22% and lower. Addition of DI water in the solution results in the formation of a thick porous silicon layer without separation from the substrate during 10 minutes. A theoretical explanation has been given to describe the phenomena of porous silicon film separation. [ABSTRACT FROM AUTHOR]

The role of hydrogen in a recently developed one-step method for the formation and separation of a thin porous Si film from the initial Si substrate is investigated by means of Raman spectroscopy and detailed morphological analysis. It is shown that hydrogen plays a crucial role in the formation and separation of the porous Si film. Micro-Raman spectroscopy reveals that hydrogen in molecular form is accumulated in the micropores and creates hydrodynamic pressure which could be strong enough to break the thin pore walls in a high-porosity layer. As a result the upper porous Si film is separated from the original substrate. The kinetics of the process is confirmed by transmission and scanning electron microscopy. [ABSTRACT FROM AUTHOR]