Photoluminescence from nanocrystalline silicon in Si/SiO2 superlattices

Abstract

Si/SiO 2 superlattices on oxidized silicon wafers were fabricated by successive cycles of silicon deposition and high-temperature thermal oxidation. Silicon films were deposited by low-pressure chemical vapor deposition at 580 °C. As-deposited silicon was amorphous, and it exhibited two weak photoluminescence (PL) peaks in the visible range, a stable one at ≅650 nm and an unstable one at 530–550 nm. By oxidation at 900 °C, a drastic increase of the stable PL peak was observed with an initial redshift from 650 to 800–900 nm and a subsequent blueshift down to 680–700 nm. Its position and intensity depended on the oxidation time. For prolonged oxidation, PL disappeared. The observed PL is attributed to silicon crystallites passivated by oxygen. Localized states at the Si/SiO2 interface limit the emitted wavelength. The PL peak from superlattices was at the same position as from one bilayer, while a superlinear increase in PL intensity was observed by increasing the number of bilayers.

Ultrafast time-resolved spectroscopy of Si nanocrystals embedded in SiO2 matrix

“…Furthermore, we should point out that the fact that the time constants are independent of the probing wavelengths in larger NCs helps us to understand that with all wavelengths we probe the corresponding particular quantized energy state, while this is not the case in smaller nanocrystals. Our study supports the general result in the literature [18,19] of a red shift of the PL in the case of small Si-NCs (d < 2.5 nm), compared to values predicted by the quantum confinement model. This red shift comes from the coupling between quantized levels and interface states between NCs and SiO 2 .…”

“…As shown from our results, the experimental method indicates a pinning of the gap in small NCs. This pinning of the gap has been theoretically predicted from Monte-Carlo simulations [17] and has been experimentally confirmed also by PL measurements [18][19][20] in porous passivated by oxygen (star symbols, in Fig. 3) and five NCs/SiO 2 bilayers (solid square, in Fig.…”

Enhanced visible photoluminescence from nc-Si/SiOx films deposited by electron beam evaporation

“…Since the observation of photoluminescence (PL) in porous Si, it has been shown that nano-scaled silicon dots in thin films are responsible for the materials' high luminescence yielding ability [1][2][3][4][5]. Recently much attention has been paid to the structure of nanocrystalline silicon (nc-Si) embedded in a SiO 2 matrix, which satisfies the demands of possible applying for silicon-based optoelectronic device technology [6][7][8][9].…”

Controllable deformation of silicon nanowires with strain up to 24%

“…High aspect ratio pillars with diameters between 50-100 nm could prove useful for core-shell type plasmonic resonators, 5 while pillars with sub-10 nm diameters have shown promising light emission characteristics. 6,7 High aspect ratio structures also have possible applications to high density electronics such as FinFETS ͑Ref. 3͒ or in DRAM devices.…”