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 p orous Si when it was oxidized at high temperatures from 800 to 900-deg rees-C in dry oxygen. The photoluminescence decay of both as-prepared and dry-oxidized porous Si was intrinsically nonexponential. As report ed by other groups, the photoluminescence lifetime, defined as 1/e tim es, decreased as the emission energy increased for as-prepared samples , and were from 60 to 200 mus. The spread in lifetimes is usually inte rpreted 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 poro us Si, however, did not depend on the emission energy and was about 10 0 mus. The result clearly shows the presence of radiative recombinatio n processes via luminescence centers, especially in dry-oxidized porou s Si.