Tin induced a-Si crystallization in thin films of Si-Sn alloys

Abstract

Effects of tin doping on crystallization of amorphous silicon were studied using Raman scattering, Auger spectroscopy, scanning electron microscopy, and X-ray fluorescence techniques. Formation of silicon nanocrystals (2–4 nm in size) in the amorphous matrix of Si1−xSnx, obtained by physical vapor deposition of the components in vacuum, was observed at temperatures around 300 °C. The aggregate volume of nanocrystals in the deposited film of Si1−xSnx exceeded 60% of the total film volume and correlated well with the tin content. Formation of structures with ∼80% partial volume of the nanocrystalline phase was also demonstrated. Tin-induced crystallization of amorphous silicon occurred only around the clusters of metallic tin, which suggested the crystallization mechanism involving an interfacial molten Si:Sn layer.

Tin-induced crystallization of amorphous silicon assisted by a pulsed laser irradiation

“…5, the threshold of structural state change occurs in the region of intensity near 10 4 W/cm 2 , that is, at the intensity 5 times lower than that used in Fig. 9), the estimated temperature will be 300 + 40·8 = 620 K ~ 350 °С, which is consistent with the data of previous studies on the tin induced crystallization of amorphous silicon [20,21].…”

“…In particular, the possibility to form Si nanocrystals in amorphous Si matrix at 2 to 5 nm sizes and the phase volume fraction up to 80% was shown by means of tin-stimulated crystallization of amorphous Si at low temperatures [18][19][20]. These experimental results interpreted by the new MIC mechanism proposed in the papers [20][21][22].…”

“…Therefore, optical absorption and corresponding heating will have substantially lower values. The nanostructures of thin tin layers in similar structures of Si-Sn-Si were observed in [20] at manufacture conditions like those used here. …”

“…The coincidence in temperatures for the beginning of structural-phase changes and tin melting confirms the mechanism of tin-induced crystallization of amorphous silicon as a process of cyclic formation and decaying of a liquid solution of silicon in tin, proposed in papers [20,21]. The discovered here two-stage MIC -the presence a long incubation period of nuclei formation and a rapid phase of their growth -is characteristic for processes of solutions decay, which may also be an argument in favor of the indicated mechanism.…”

“…They are used to study the effects of laser radiation on pre-formed nanocrystals. Determination of the crystal sizes (L) and the fraction (X C ) of volume occupied by crystals in the samples under investigation was carried out by using computer approximation of the Raman spectra as based on the theory of spatially bounded phonons [24,25] with simplifications described in [20]. In particular, it was found that in the samples Nos 1, 2, 3, 6, 6-1 initial parameters of crystallinity make up: L = 1.5 µm, X C = 48%.…”