STUDY OF LUMINESCENT POROUS POLYCRYSTALLINE SILICON THIN-FILMS

Luminescent porous poly-Si thin films can be obtained by electrochemic al etching of phosphorus-doped poly-Si films deposited by low-pressure chemical-vapor deposition, As-deposited poly-Si film has no photolumi nescence but all porous poly-Si films, large area or micron-size patte rns, show comparable orange-red photoluminescences to those obtained f rom crystal Si. High-resolution atomic force microscopy and scanning e lectron microscopy analyses show that all porous poly-Si films have sm ooth surfaces and uniform thicknesses. and are composed of Si grains ( similar to 150 nm) with nanopores (similar to 20 nm) formed around the surfaces. The pores increase with anodization rimer and grow preferen tially along the poly-Si grain boundaries and the Si [100] crystal dir ections, The evolution of the microstructure is analogous to that of t he etching of a coral ball layer due to sea water. (C) 1996 American V acuum Society.