General characteristics of amorphous silicon alloys. Hydrogenation, crystallization and polymerization

This article presents the results of studies of the physical properties of hydrogenated amorphous thin films of a-Si_1-xG_ex:H and a-Si_1-xC_x:H alloys obtained by plasma chemical deposition. The optical constants (n, n, a, R, d) and the band gap of the films under study (E₀ = 1,05-3,00 eV) were determined. Based on a study of the optical properties of various deposition modes (T_pod, d, H₂), the substrate temperature, film thickness and the level of hydrogenation of the alloys are characterized by different structural phases. With a change in technological parameters, various structural and polymer phases of crystallites are also obtained: nanotubes, nanowires, nanoparticles, quantum wells, quantum dots, graphenes, graphites, decanters, fullerenes, diamond particles, clusters, etc.

The structure of the deposited nc-Si:H films is mixed-two-phase and consists of nc-Si:H nanocrystallites «distributed» in an amorphous network. Annealing of crystalline films at a temperature of 700 ⁰C increases the crystal­lite size to 50-100 A⁰ in diameter, and the conductivity changes slightly. Also, when hydrogen is introduced into an amorphous silicon film at low temperatures (T_s < 100 °C) with a higher hydrogen content (~ 30 atm.% or more), the material contains an excess of the SiH₃ group, as well as slightly more hydrogen in the polymer form (SiH₂)_n. The con­centration of carbon and hydrogen in a-Si_1-xC_x:H films depends on the deposition conditions and the initial gas mixture of SiH₄, CH₄, H₂. Depending on the choice of modes, with increasing concentrations of hydrogen H₂ and CH₄, films are deposited in polymer form.

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