Takaaki Kamimura

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.

Measurement and analysis of photocurrent transient characteristics for hydrogenated amorphous-silicon photodiodes

The relations between the photocurrent transient after the end of steady-state illumination for hydrogenated amorphous silicon photodiodes and the related film properties for undoped hydrogenated amorphous silicon prepared by mercury-sensitized photochemical vapor deposition are investigated. The photocurrent transient characteristic indicates significant correlations with the film properties, such as electron drift mobility ( mu /sub d/), silicon dangling bond density (N/sub s/), a minimum in the density of states near the Fermi level (N/sub min/), and space-charge density (N/sub i/). The photocurrent transient decay decreases with increasing mu /sub d/ and with decreasing N/sub s/, M/sub min/, and N/sub i/. This result was confirmed by a model analysis. >

Characteristics for a-Si:H Films Prepared by Mercury-Sensitized Photochemical Vapor Deposition

The density of states in a-Si:H, prepared by mercury-sensitized photo-CVD, was measured by the space-charge-limited current method. The density of Si dangling bonds (Ns) was measured by the electron spin resonance method. Ns and a minimum of the density-of-state near the Fermi level (Nmin) indicated the same tendency versus substrate temperature, which showed a good correlation between Ns and Nmin. Both Ns and Nmin showed a minimum value near substrate temperature of 200°C. Photosensitivity reached more than 1×106 for the sample.

Correlation between Si-H2 bond density and electron drift mobility in a-Si:H films prepared by photochemical vapor deposition

The correlation between Si-H2 bond density and electron drift mobility in a-Si:H films has been investigated by using the dependence of the film properties on the silane gas pressure in mercury-sensitized photochemical vapor deposition. It was found that the electron drift mobility decreased with increasing the Si-H2 bond density, when the hydrogen contents were about the same amount.

Selective Deposition of Silicon by Mercury Sensitized Photochemical Vapor Deposition

The authors have developed a low-temperature process for selective deposition of silicon by mercury sensitized photochemical vapor deposition (Photo-CVD) without using ultraclean technology. It was found that hydrogen radical pretreatment was required to obtain selective deposition. There was an incubation period for not only SiO2 surface but also Si surface. It was confirmed that mercury sensitized Photo-CVD is a promising method for selective deposition process at low temperature using large-area glass substrate.

Influence of nitrogen incorporation in hydrogenated amorphous silicon films prepared by photochemical vapor deposition

The influence of nitrogen incorporation in a-Si:H films by mercury-photosensitized decomposition of a silaneammonia gas mixture was investigated. It was found that there are two different film structures of a-Si:H films. In a high nitrogen concentration, nitrogen is one of the elements of the a-SiNx alloy. On the other hand, in a low nitrogen concentration, nitrogen plays the role of a dopant in a-Si:H, and nitrogen-induced localized states are created at around 0.5 eV above the valence band edge.

The Selective Deposition of a Silicon Film on Hydrogenated Amorphous Silicon by Mercury Sensitized Photochemical Vapor Deposition

The authors have developed a low-temperature process for the first time for the selective deposition of a silicon film on hydrogenated amorphous silicon (a-Si:H) and on silicon nitride (SiNx) surfaces by mercury sensitized photochemical vapor deposition (Photo-CVD). The selective deposition of Si films was able to be achieved by hydrogen radical cleaning for 1 minute prior to the deposition. There were two different incubation periods for the a-Si:H and SiNx surfaces. Selective deposition was obtained by using this difference in the incubation periods between the deposition on an a-Si:H surface and on a SiNx surface. The field effect mobility and the off leakage current for thin film transistor (TFT) of the fabrication by using this selective deposition technique were of the 0.6 cm2 V-1 s-1 and 10-11 A order, respectively. It has been confirmed that photo-CVD is a promising method for the selective deposition process at a low temperature using a large-area glass substrate.

A new, laminar flow photo-CVD method for preparing hydrogenated amorphous silicon films

A new, laminar flow type photochemical vapor deposition method has been applied to prepare a-Si:H films. The main feature of this method is introduction of Ar gas as a flow down gas through the lower part of the quartz window into the reaction chamber to keep the window highly transparent. The high deposition rate (150 A/min) of the a-Si:H film has been stably maintained by optimizing the flow rate for each gas into the chamber. Utilizing this new method, we have been able to realize high quality films with low impurity content, high resistivity (>10 11 Ω cm), low dangling bond density (5×10 15 cm -3 ), etc