Thin Solid Films 425 (2003) 175–184 0040-6090/03/$ - see front matter  2002 Elsevier Science B.V. All rights reserved. PII:S0040-6090 Ž 02 . 01113-6 The effect of annealing conditions on the red photoluminescence of nanocrystalline Si y SiO films 2 Xiaochun Wu *, Alpan Bek , Alexander M. Bittner , Ch. Eggs , Ch. Ossadnik , S. Veprek a, a a b b b Max-Planck Institut fuer Festkoerperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany a Institut fuer Chemie Anorganischer Materialien, Technische Universitaet Muenchen, Lichtenbergstr. 4, D-85747 Garching, Germany b Received 18 June 2002; received in revised form 24 October 2002; accepted 12 November 2002 Abstract Nanocrystalline Si (nc-Si) embedded in a SiO matrix, fabricated by plasma CVD and a subsequent post-treatment shows a 2 broad red photoluminescence (PL). In this paper, the effects of annealing temperature, atmosphere and time on the red PL from 1.75 to 1.5 eV have been investigated in detail. It is found that the spectral shift and the PL intensity from 1.75 to 1.5 eV show a strong and unique dependence on annealing conditions. For a PL approximately 1.75 eV, upon 400 8C forming gas annealing, the spectral shift and the peak intensity versus accumulation annealing times show a novel temporal oscillation. This unique dependence and the novel temporal oscillation behavior, which have not been reported in porous silicon, exclude nc-Si itself as the source of the red PL. Instead they favor oxygen thermal donors (TDs)-like defect states as PL centers. This is in consensus with our earlier results of defect studies using electron spin resonance in this system. Furthermore, two PL centers in this red PL were distinguished according to their variance in annealing temperature- and time-dependence. The spectral change between 1.5 and 1.75 eV upon annealing conditions can be qualitatively explained by using the formation and annihilation kinetics of two oxygen TDs-like defect state.  2002 Elsevier Science B.V. All rights reserved. Keywords: Photoluminescence; Thermal donors; Annealing conditions 1. Introduction Since the discovery of a strong visible photolumin- escence (PL) in porous silicon (PS) in 1990 w1x, many experiments have been carried out in the hope of a potential application of Si in optoelectronic devices. Although a large volume of experimental data is avail- able in the literature, a detailed understanding of the PL mechanism has not been achieved yet w2,3x. So far, mainly two models are proposed to interpret the origin of the visible PL: (1) pure quantum size effect (QSE) w4x and (2) surface state model w5x. As is well-known, for PL phenomena, two important processes are the formation of photoexcited carriers (excitation process) and the radiative recombination of the photoexcited carriers through PL centers (luminescence process). For the pure QSE, it is considered that both the excitation *Corresponding author. Tel.: q49-711-689-1432; fax: q49-711- 689-1709. E-mail address: x.wu@fkf.mpg.de (X. Wu). process and the PL process originate from nanocrystal- line Si (nc-Si). For the surface state model, it is considered that the excitation process originates from nc-Si and the PL process originates from a special surface state. As for the surface state model, various surface species such as siloxene w6x, polysilanes w7x, SiH w8x, Si band-tail states w9x, interfacial oxide-related 2 defect centers w2x, nonbridging oxygen hole centers w10x, and oxyhydride-like emitters w11x have been suggested as the source of the visible PL. Among them, interfacial oxide-related defect centers are widely accepted, but still the detailed structures of these centers are unclear w2,10–17x. Gole et al. even suggested a third model; i.e. both the light excitation process and the PL process are due to a surface-bound silanone-based silicon oxyhydri- de fluorophor, based on their investigations on the origin of the PL in PS w11–13x. Recently, studies from Wolkin et al. seemed to clarify some disputes among the source of visible PL in PS w18x. They pointed out that depend- ing on the size of PS and on the interfacial chemical