Si-H Bond Density Research Articles

Hydrogenated Amorphous Silicon Films Prepared by Mercury Sensitized Photochemical Vapor Deposition

ABSTRACTHydrogenated amorphous silicon (a-Si:H) films were prepared by mercury photosensitized decomposition of silane using a low-pressure mercury lamp. The deposition rate showed an activation type for substrate temperature (the activation energy: 0.13 eV), because the deposition rate would be determined by the rate of hydrogen elimination from the hydrogen saturated surface. Moreover, the relationship was found between the Si-H2 bond density in a- Si:H films and the gas phase reactions.

Bonding and electrical properties of boron-doped microcrystalline SiNx:H films

Microcrystalline (μc-) SiNx:H films have been prepared by rf glow discharge of SiH4-B2H6-N2-H2 mixtures as a function of the substrate temperature Ts, N2 gas ratio RN, and B2H6 gas ratio RB. The bonding, electrical, and optical properties have been investigated. Crystallization is observed at Ts below 350 °C and above 700 °C, at RN below 0.04, and at RB below 5×10−3. The ratio of the volume fraction ρ of the crystalline phase to the crystallite size δ is roughly constant. The Si-N bond density agrees well with the Si-H bond density, indicating enhanced formation of N-SiH bonds. For the films with larger ρ or δ, N and H atoms are segregated in a part of the amorphouslike boundary region between crystallites, but those for the films with lower ρ or δ are uniformly distributed in the boundary region. The optical gap is mainly characterized by the N and H contents. As the film is deposited at a preparation condition giving transformation from μc to amorphous structure, the dark conductivity and photoconductivity abruptly decrease, and the slope K in the Tauc equation for optical absorption is a maximum. Furthermore, at this condition, we obtained B-doped μc-SiNx:H films with both wide gap (∼1.9 eV) and high conductivity (10−1–10−2 Ω−1 cm−1).

Effect of Hydrogen Dilution of Silane in Hydrogenated Amorphous Silicon Films Prepared by Photochemical Vapor Deposition

Hydrogenated amorphous silicon (a-Si:H) films were prepared by mercury photosensitized decomposition of silane-hydrogen (or-helium) gas mixtures. In hydrogen dilution, a-Si:H films were deposited from 20-100% of the silane fraction and hydrogenated amorphous-microcrystalline mixed-phase silicon (µc-Si:H) films were deposited for less than 10% of the silane fraction. The Si-H2 bond density and optical gap for a-Si:H films increased upon decreasing the silane fraction. The preferential orientation of the crystallites in µc-Si:H films was greatly changed by the silane fraction. However, the film characteristics did not change upon helium dilution. It was found that the hydrogen radical plays a significant role in the film-deposition process. Large-grain-size µc-Si:H films have been obtained, as compared with the grain size for films made by the conventional glow-discharge technique.