Mechanism of Tin-Induced Crystallization in Amorphous Silicon

Abstract

Formation of Si nanocrystals in amorphous Si-metallic Sn film structures has been studied experimentally, by using the Auger spectroscopy, electron microscopy, and Raman scattering methods. The results are analyzed in comparison with recent results on the crystallization of tin-doped amorphous Si. A mechanism of silicon transformation from the amorphous to the nanocrystalline state in the eutectic layer at the Si-Sn interface is proposed. The mechanism essence consists in a cyclic repetition of the processes of formation and decay of the Si-Sn solution. The application aspect of this mechanism for the fabrication of nanosilicon films used in solar cells is discussed. K e y w o r d s: silicon, nanocrystals, thin films, metal-induced crystallization, tin, solar cell.

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].…”

“…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.…”

“…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]. It differs significantly from those known for other metals [13,[15][16][17].…”

“…3, this effect has a threshold in the region of 5·10 4 W/cm 2 , which may be related, in particular, with achievement of the melting temperature for the tin layer in the investigated structures. According to [21,22], the transition of tin into a liquid state is a prerequisite for MIC of amorphous Si.…”

Tin-Induced Crystallization of Amorphous Silicon under Pulsed Laser Irradiation

“…In particular, a possibility to form Si nanocrystals 2-7 nm in dimensions and with a phase volume fraction of up to 80% in the a-Si matrix with the help of the low-temperature tin-induced Si crystallization was demonstrated in [18][19][20]. Those experimental results were interpreted with the use of a new mechanism of MIC, which was proposed in works [20][21][22] and considerably differs from those known for other metals [13,[15][16][17]. According to this mechanism, silicon nanocrystals are formed as a result of the cyclic repetition of their formation and decay pro-cesses in the supersaturated solution of silicon in tin that emerges in a narrow eutectic layer at the a-Si/Sn interfaces between tin microdroplets and the bulk of amorphous Si.…”