AVS 52nd International Symposium
    Plasma Science and Technology Wednesday Sessions
       Session PS+TF-WeM

Paper PS+TF-WeM4
Multi-hollow Plasma CVD Method for Depositing Cluster-free a-Si:H Films

Wednesday, November 2, 2005, 9:20 am, Room 302

Session: Plasma Enhanced CVD and ALD
Presenter: K. Koga, Kyushu University, Japan
Authors: K. Koga, Kyushu University, Japan
K. Bando, Kyushu University, Japan
M. Shiratani, Kyushu University, Japan
Y. Watanabe, Kyushu University, Japan
Correspondent: Click to Email
The three major limitations of a-Si:H solar cells are 1) light-induced degradation of cell efficiency, 2) a low deposition rate, and 3) a low cell efficiency. We have developed a multi-hollow plasma CVD method for depositing cluster-free a-Si:H films, since films incorporating less amount of a-Si:H nano-particles (hereafter refereed to as clusters) show better stability.@footnote 1@ For the method, powered and grounded electrode of 70 mm in diameter, which had 24 holes of 5 mm in diameter, were placed at a distance of 2 mm. Discharges were sustained in the holes using a VHF power source. A short gas residence time of ~ ms in the discharge regions suppressed growth of clusters and gas viscous force drives clusters toward the downstream region. Therefore, cluster-free a-Si:H films can be deposited on substrates set in the upstream region. Stability of the films against light soaking was evaluated with their defect density measured by ESR and a fill factor FF of a Schottky cell having a structure of Ni/a-Si:H/n type Si. The initial defect density of a film deposited at 0.12 nm/s is 3.5x10@super 15@cm@super -3@ and that after light soaking (7.5 hours under 2.4 SUN) is 3.7x10@super 15@cm@super -3@. The cell using a film deposited at 0.2 nm/s has a rather high stabilized FF of 0.50 and a small degradation ratio of 2.0 %. A higher deposition rate up to 0.66 nm/s can be obtained by utilizing a higher discharge power. Thus the multi-hollow plasma CVD method is effective in overcoming the three limitations for a-Si:H solar cells. @FootnoteText@ @footnote 1@K. Koga, N. Kaguchi, M. Shiratani and Y. Watanabe, J. Vac. Sci. Technol. A 22, (2004) 1536.