A MICROSCOPIC ROLE OF IMPURITY ON GROWTH SURFACE OF MICROCRYSTALLINE SILICON - TOWARDS LARGER GRAIN SIZE AND LOWER DEFECT DENSITY-

摘要

Ultra clean plasma CVD(Chemical Vapor Deposition)process opens the doorway to clarify the role of impurities in the growth process ofμ c-Si:H. A reduction of impurity levels during the growth extends the temperature range for crystalline formation to lower side,i.e.,high-crystallinity μc-Si:H formation even at room temperature, substantially reduces midgap defect density at 200 deg C, and enlarges crystalline grain size at 350 deg C .These results imply significant effects of impurities on crystalline formation, the surface of which is covered with hydrogen and thus can be considered to be chemically inactive. The crystalline-to-amorphous transition at higher temperature of ～450 deg C is induced by a loss of surface hydrogen coverage due to thermal hydrogen desorption irrespective of the effect of oxygen impurity.