Articles you may be interested inPhotoluminescence properties and crystallization of silicon quantum dots in hydrogenated amorphous Si-rich silicon carbide films

Annealing temperature and barrier thickness effect on the structural and optical properties of silicon nanocrystals/SiO2 superlattices Raman study of very thin ͑р3.5 nm͒ Si layers constituting Si/SiO 2 superlattices and grown by molecular beam epitaxy is described. The Raman spectra show systematic dependence on thickness of the Si layers, which highlights the variety of disordered microstructures in the Si/SiO 2 superlattices. A clear change in the vibrational properties is found to occur in the 0.8-3.5 nm thickness region. In particular, the Raman spectra are typical for amorphous silicon for the thicker layers, and the characteristic phonon band disappears for the thinner layers, presumably representing another form of Si coordination with a small Raman scattering cross section. In addition, absorption of the material changes essentially with the Si-layer thickness. Photoluminescence is detected from the Si/SiO 2 superlattices, the superlattices with 1.2 and 1.8 nm Si layers being the most efficient emitters among our samples, and the photoluminescence is blueshifted with the decrease of the Si-layer thickness. The Raman spectra show no sign of nanocrystalline structure at any thickness of the as-deposited Si layers so that the observed photoluminescence cannot be connected with Si nanocrystallities. Annealing strongly changes the Raman and photoluminescence spectra, a well-ordered Si phase appears in the superlattices, but its increase does not correlate with the photoluminescence, which further disregard it as an emitter. Nevertheless, the emitting phase is not identified in the Raman spectra.

A quantitative model of a Si/SiO2 superlattice (SL) is developed and applied to Raman and photoluminescence (PL) measurements. By analyzing the experimental reflection spectra of Si/SiO2 SLs on Si and Al substrates, we obtained optical parameters of amorphous Si layers with thickness below 4 nm. Both refractive index and extinction coefficient are found to decrease with Si-layer thickness, and this behavior reflects interaction of the Si network and the oxide surrounding. Interference-induced modification of Raman scattering and PL is quantitatively studied for Si/SiO2 SLs on Si and Al substrates, and the developed optical model describes well all observed features. PL spectra of the Si/SiO2 SLs are found to change under Ar+-laser irradiation, and this effect of laser annealing becomes stronger for thinner Si layers. For 1-nm-thick Si layers, a prolonged laser exposure decreases the PL intensity at 550 nm by a factor of 10 and red-shifts its maximum by about 50 nm, which indicates essential reorganization of the network under laser irradiation.

No abstract

No abstract