Preparation and Properties of High-Quality a-Si Films with a Super Chamber : Separated Ultra-High Vacuum Reaction Chamber

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Abstract
A separated ultra-high vacuum (UHV) reaction chamber system, called the super chamber, has been newly developed. A background pressure of 10-9 Torr was obtained, and the impurity concentrations of oxygen, nitrogen and carbon in an a-Si film fabricated in the super chamber were 2×1018 cm-3, 1×1017 cm-3, and 2×1018 cm-3, respectively. The space charge density and the ESR spin density of the a-Si film were 5×1014 cm-3 and 2×1015 cm-3, respectively. These values were much lower than those for films fabricated in a conventional chamber. The ratio of the light-induced degradation in the photoconductivity of the a-Si film was also small compared with that of conventional a-Si films. A conversion efficiency of 11.7% was obtained for a glass/textured TCO/pin/Ag a-Si solar cell, whose i-layer was fabricated in the super chamber.