Intense RT Visible Photoluminescence from Anodized Amorphous and Nanocrystalline Silicon Films

Heavily Boron-doped micrometer-thick amorphous (a-Si:B:H) or nanocrystalline (nc-Si) silicon layers have been deposited on a variety of conductive substrates by the 50 KHz PECVD of SiH4 / B2H6 / H2 mixtures at 320°C. These films have been partially electro-oxidized in a HF solution and then anodically oxidized in water in a manner similar to that yielding luminescent porous monocrystalline silicon layers (PcSL). Although the anodized films are x-ray amorphous, they yield intense luminescence properties at room temperature very similar to those of anodically oxidized PcSL with a similar vibrational spectrum. In both anodically oxidized materials, aging is shown to improve the external quantum efficiency. In amorphous anodized layers, optical microscopy under UV excitation showed strongly luminescent strain-related heterogeneities (20 μm in diameter) connected by non luminescent channels. The incidence of our results on the current debate about the origin of visible room-temperature luminescence in porous silicon and Si:O:H systems is discussed.