PHOTOLUMINESCENCE MECHANISMS OF POROUS SI OXIDIZED BY DRY OXYGEN

Photoluminescence mechanisms in porous oxidized Si were investigated. We observed marked enhancement in the photoluminescence intensity of porous Si when it was oxidized at high temperatures from 800 to 900-degrees-C in dry oxygen. The photoluminescence decay of both as-prepared and dry-oxidized porous Si was intrinsically nonexponential. As reported by other groups, the photoluminescence lifetime, defined as 1/e times, decreased as the emission energy increased for as-prepared samples, and were from 60 to 200 mus. The spread in lifetimes is usually interpreted in terms of the size distribution of Si microcrystals, and the long lifetime on a microsecond time scale is explained by a carrier's tunneling model. The photoluminescence lifetime for dry-oxidized porous Si, however, did not depend on the emission energy and was about 100 mus. The result clearly shows the presence of radiative recombination processes via luminescence centers, especially in dry-oxidized porous Si.