COMPOSITION OF POROUS SILICON

Samples of porous Si were prepared from p-type, 10 OMEGA cm Si under 10 mA cm-2 anodization in aqueous HF (mostly 50%) for 5 min. These showed photoluminescence peaking at 835 nm at 10 K, with full width half maximum of 78 nm, the data showing little change up to 150 K. High-resolution scanning electron microscopy showed column widths of 2-6 nm in the 2-mum-thick films. Hydrogen content was measured by the method of elastic recoil detection, and carbon and oxygen by nuclear reaction analysis. The fluorine content was measured by particle-induced gamma emission as 0.03 at. %. The Si, O, C, and H contents were confirmed by Rutherford backscattering analysis, as approximately Si2.5O1.2C1.3H1.2. The data, particularly the low Si content, are not inconsistent with the presence of complex chemical compounds in the films, although any role they play is not established.