Behavior of Hydrogen During Crystallization of Thin Silicon Films Doped with Tin

Abstract

The behavior of a hydrogen impurity in the course of crystallization of thin silicon films doped with tin (a-SiSn films) has been studied. It is found that the band located at about 2000-2200 cm −1 and corresponding to the IR absorption at silicon-hydrogen bonds is absent from the spectra of as-deposited (at a temperature of 300 • C) a-SiSn films with Sn contents within the interval of 1-10 at.%. In undoped thin silicon films (a-Si films), the hydrogen content diminishes below the sensitivity threshold of the measurement technique only after the annealing of the specimens at 700 • C. The absence of hydrogen in a-SiSn films is in good agreement with the results of EPR studies and the results of Raman scattering studies of structural transformations in thermally treated films. It is shown that the formation of crystalline phases in a-SiSn occurs at lower temperatures as compared to those in a-Si, with a correlation taking place between the crystallization temperature for Si clusters and the concentration of the tin impurity. Taking into account that tin reduces the temperature of the hydrogen effusion from the film volume and, accordingly, stimulates the ordering in the specimen structure, it is possible to consider that hydrogen impurity takes part in the processes that result in a decrease of the crystallization temperature for a-SiSn. K e y w o r d s: thin silicon films, crystallization, tin doping, hydrogen.

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].…”