Study of luminescent porous polycrystalline silicon thin films

Luminescent porous poly-Si thin films can be obtained by electrochemical etching of phosphorus-doped poly-Si films deposited by low-pressure chemical-vapor deposition. As-deposited poly-Si film has no photoluminescence but all porous poly-Si films, large area or micron-size patterns, show comparable orange-red photoluminescences to those obtained from crystal Si. High-resolution atomic force microscopy and scanning electron microscopy analyses show that all porous poly-Si films have smooth surfaces and uniform thicknesses, and are composed of Si grains (∼150 nm) with nanopores (∼20 run) formed around the surfaces. The pores increase with anodization time, and grow preferentially along the poly-Si grain boundaries and the Si 〈100〉 crystal directions. The evolution of the microstructure is analogous to that of the etching of a coral ball layer due to sea water.