COMPARISON OF MICROSECOND PHOTOLUMINESCENCE DECAY BETWEEN AS-PREPAREDAND DRY-OXIDIZED POROUS SI

Photoluminescence (PL) decay for as-prepared and dry-oxidized porous S i following by a nitrogen pulse laser excitation is reported. The PL d ecay of both samples is nonexponential. For the as-prepared samples, t he PL lifetime decreases from 200 to 60 mus as the PL emission energy increases from 1.55 to 1.90 eV. The spread in values can be interprete d in terms of nonradiative tunneling of carriers between Si microcryst als. For the dry-oxidized samples, the PL lifetime depends little on t he emission energy, and is about 100 mus. On the basis of these result s, we conclude that photoluminescence cannot be explained by the tunne ling model alone, suggesting that luminescence centers play a role in determining the PL mechanism of porous Si.