Influence of High Temperature Annealing on the Structure and the Intrinsic Absorption Edge of Thin-Film Silicon Doped with Tin

Abstract

Influence of isochronal annealing in the range of 350-1100 • C on the structural properties and the intrinsic absorption edge in thin silicon films doped with tin (a-SiSn) has been studied. It is found that as-deposited a-SiSn films with a tin content of about 4 at.%, unlike undoped a-Si ones, contain silicon nanocrystals with a crystallite size of about 4 nm and a crystalline fraction of about 65%. It is shown that, in the course of isochronal annealing of a-SiSn specimens in the interval of 350-1100 • C, the size of silicon nanocrystals in the amorphous matrix gradually increases to about 7 nm, and the fraction of crystalline phase to about 100%. Crystallization in undoped a-Si is observed only after the annealing at temperatures above 700 • C. The influence of tin on the optical band gap in a-Si as a function of the isochronal annealing temperature is analyzed.K e y w o r d s: thin-film silicon, doping with tin, crystallization, optical band gap, isochronal annealing.

Formation of Nanocrystalline Silicon in Tin-Doped Amorphous Silicon Films

“…In order to change the phase composition in precipitated films, the latter were subjected to the isochronous annealing for 20 min in the argon atmosphere within the temperature interval from 300 to 750 ∘ C with an increment of 50 ∘ C. The phase composition of the films was studied by analyzing their Raman spectra. A detailed description of the method can be found in our previous works [8,9]. The Raman spectra were registered at room temperature on a Jobin Yvon T-64000 spectrometer using the excitation radiation of an Ar + laser with a wavelength of 488 nm.…”

“…The average sizes of silicon crystallites and the fraction of the crystalline phase were estimated by resolving the Raman spectra into bands corresponding to the amorphous and crystalline phases in the framework of the spatial phonon confinement model [18][19][20]. The detailed information concerning a b the method of producing the a-SiSn films, their impurity composition, and structural and optical characteristics can be found in works [7][8][9].…”

“…According to this assumption, the larger the size of tin clusters, the larger the size of silicon crystallites formed in the film bulk. Let us also suppose that the metallic tin clusters that are formed in the film bulk have the same size, and every of those clusters can dissolve such a number of Si atoms from the amorphous matrix that is sufficient for the formation of silicon nanocrystals with dimensions equal to those experimentally determined in works [8,9] (see Fig. 1).…”

“…It is known that even the application of the same metal may lead to the formation of nanocrystalline silicon in some cases and microcrystalline silicon in the others. For example, we showed earlier that the crystallization temperature in the amorphous silicon [7][8][9] and silicon suboxide [2] films that were tindoped during their precipitation becomes lower, and the formation of nc-Si with crystallite sizes up to 10 nm takes place in them. The authors of work [14] reported on the formation of nanocrystalline silicon (<10 nm) in films obtained by simultaneously evaporating silicon and aluminium.…”

“…The physical properties of thin silicon and silicon suboxide films depend to a large extent on the ratio between the numbers of particles of the amorphous and nanocrystalline phases, as well as on the size and concentration of silicon nanocrystals [2,3,[7][8][9]. Nanocrystalline inclusions are also believed to partially relieve mechanical stresses in the amorphous matrix, thus resulting in a possibility to form a less strained network with a fewer number of weak bonds, which is more robust to degradation under the action of external factors [6,7].…”