Role of hydrogen in the photoinduced evolution of porous silicon luminescence

Abstract

Photo-induced post preparation evolution effects in porous silicon were studied by IR, EPR, photoluminescence, and hydrogen effusion spectroscopies. The results show that two independent mechanisms are present during the photo-induced evolution. We also show that hydrogen photo-effusion takes place, in agreement with our previously proposed model. Photo-effusion experiments performed in vacuum, combined with IR and photoluminescence spectroscopies allow to discriminate the competing mechanisms present in the evolution of the photoluminescence.

Photo-oxidation effects of light-emitting porous Si

“…Several authors studied the photo-oxidation effects of lightemitting PSi samples. 10,24,[27][28][29][30][31] Some results, however, contradict the fundamental PL properties. For example, some authors reported a redshift during photo-oxidation, 27 while others observed a blueshift.…”

“…1,2 However, the as-prepared PSi surfaces have been shown to be unstable in room air especially under light illumination. [3][4][5][6][7][8][9][10] Several authors, therefore, investigated to stabilize PSi surfaces using various techniques, such as rapid thermal oxidation, 11 high-pressure water vapor oxidation, 12,13 carbon termination, 8,14 inorganic or organic film coating, 6,9,[15][16][17] anodic oxygen termination or oxidation, 7,18-20 and wet chemical treatment. 21 Hydrogen ͑H͒ is known to passivate Si surfaces by binding to Si dangling bonds.…”

“…3,4,10,24 Infrared measurements devoted the decrease in the Si-H stretching vibrations at ϳ2100 cm −1 after UV illumination. 3,4,24 A clear increase in the H 2 partial pressure in a vacuum chamber was also observed by illuminating light centered at 400 nm on the PSi surface.…”

“…3,4,24 A clear increase in the H 2 partial pressure in a vacuum chamber was also observed by illuminating light centered at 400 nm on the PSi surface. 10 It is therefore easily expected that the incorporation of oxygen occurs during UV-or blue-light-induced H effusion, resulting in the photo-oxidation of PSi surface. In fact, Koropecki et al 25 reported that the H effusion experiments corroborate with the photo-oxidation by taking place in a preferential manner at the expense of H bonded as dihydride.…”

Infrared study of the oxidation of porous silicon: evidence of surface modes

“…As we demonstrated previously [3], during the first stages of photo-oxidation, oxygen atoms displace hydrogen atoms preferentially from di-hydride sites. Although the breaking energy of Si-Si bonds is lower than that of Si-H (E(Si-H))ones, molecular H 2 formation is involved in the process, as usually occurs in effusion experiments [14,15]. The actual amount of energy needed to overcome the energy barrier E B should be: , labelled IP in Fig.…”