Hiroomi Miyahara

Two-Dimensional Spatial Profile of Volume Fraction of Nanoparticles Incorporated Into a-Si:H Films Deposited by Plasma CVD

Using an optical-scanning method, we obtained 2-D spatial profile of deposition rate of hydrogenated amorphous silicon (a-Si:H) films deposited by a multihollow discharge plasma CVD with a high spatial resolution. From the profile, we deduced 2-D spatial profile of the volume fraction of nanoparticles incorporated into films, since nanoparticles affect optical and electronic properties of a-Si:H films.

Cluster incorporation control for a-Si:H film deposition

To study the effects of clusters on the light induced degradation and control their deposition into films, we have developed a multi-hollow plasma CVD method by which the incorporation of clusters is reduced in the upstream region using the gas flow that drives clusters formed in discharges toward the downstream region of the reactor. Thus, we can simultaneously deposit films in which the volume fraction of clusters incorporated into films varies by changing the position of the substrate in the reactor. A-Si:H films with a lower volume fraction of clusters tend to show better stability against light exposure.

Plasma CVD for Producing Si Quantum Dot Films

Si quantum dot films are deposited using a multi-hollow discharge plasma CVD method. For the method, Si nano-crystallites of a small size dispersion and radicals are produced using H2+SiH4 VHF discharges, and then they are co-deposited on to a substrate to form Si quantum dot films, that is, a-Si:H films containing nano-crystallites. The films have a wide optical band gap of 1.8 eV and a large optical absorption coefficient similar to those of a-Si:H films. They also have a low initial defect density below 1 times 1016 cm-3 and show high stability against light soaking. These results suggest that the Si quantum dot films are promising materials for solar cells