Silicon nanoporous pillar array: a silicon hierarchical structure with high light absorption and triple-band photoluminescence.

A silicon hierarchical structure, silicon nanoporous pillar array (Si-NPA), was prepared by a hydrothermal etching method. The architecture of Si-NPA was characterized to be a regular array of micron-sized, quasi-identical and nanoporous silicon pillars with an additional porous layer beneath the array. The pore walls were proved to be consisted of a SiO(x) matrix and dispersive silicon nanocrystallites. An integral reflectivity below 4% was achieved in the wavelength range of 240-2400 nm. Three photoluminescence bands, one blue and two red, were observed at room temperature and attributed to the recombination processes through band-to-band transition and luminescent centers, respectively. The structural and physical properties indicate that Si-NPA might be as both a functional silicon nanostructure and a template for assembling silicon-based nanocomposites in fabricating optoelectronic nanodevices.