Study of porous silicon layer for epitaxial thin film silicon solar cells

This paper deals with the investigation of the restructuration impact of porous silicon (PS) during annealing on epitaxial layers properties. The dependence of surface roughness of porous silicon on the annealing time has been studied by AFM. Two kinds of roughness were observed: at a nanometric scale roughness decreases with annealing time showing a densification of the porous silicon while at a micrometric scale roughness increases with time by the apparition of large craters. This phenomenon is well explained by classical sintering theory. Then epitaxial layers were grown by VPE on porous silicon with different annealing time in order to quantify porous silicon restructuration effect on layers properties. Secco etch revealed that the defect density in VPE layers increases significantly with annealing time. This is confirmed by Hall measurements and diffusion length measurements which decrease with annealing time, these results show that porous silicon restructuration has a significant effect on epitaxial layer crystal quality and their electrical properties.