Anneal effect on multipeak photoluminescence properties of porous silicon pillar arrays

Porous silicon pillar array (PSPA) samples with broad photoluminescence (PL) from ~380 to ~800 nm were prepared by a hydrothermal etching method and found to be a hierarchical structure of silicon. The broad PL of PSPAs, which arises from four separate origins, could be tuned by varying annealing temperature and protective gas. In addition, the elemental compositions and their valence states change with annealing temperature and ventilation conditions. The results show that as the numbers of Si-Hx and Si-Si-Si bonds in the PSPAs decreased, different change of the intensities of red and pink PL bands. Moreover, at high annealing temperature, the PSPA samples contained only Si-O-Si bonds and only green and blue PL bands were observed. We attribute the pink and red PL bands to quantum confinement and quantum confinement/luminescence center emissions caused by the Si nanodots, and the blue and green emissions to two different luminescence centers associated with oxygen vacancies.