FABRICATION OF P-CHANNEL POLYCRYSTALLINE SI1-XGEX THIN-FILM TRANSISTORS BY ULTRAHIGH-VACUUM CHEMICAL-VAPOR-DEPOSITION

In this report, we present a novel approach for fabricating polycrystalline silicon-germanium thin-film transistors at low temperatures (less than or equal to 550 degrees C). A bottom gate configuration is used for this approach, and an i-Si1-xGex/i-Si/p(+)-Si1-yGey multilayer is deposited sequentially on the gate oxide using an ultra-high vacuum chemical vapor deposition technique. The i-Si1-xGex serves as the channel while the i-Si is used as a buffer layer for allowing p(+)-Si1-yGey to be etched selectively on. p-channel thin-film transistors with a held-effect mobility of 13 cm(2)/V s were achieved using this method, which is superior to those grown by low pressure chemical vapor deposition. Our results indicate that the deposition of poly-Si1-xGex/poly-Si multilayer structure would be a promising way for polycrystalline thin-film device applications.