Fabrication of p-channel polycrystalline Si_1-xGe_x 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 (≤550°C). A bottom gate configuration is used for this approach, and an i-Si _1-xGe_x/i-Si/p⁺-Si_1-yGe_y multilayer is deposited sequentially on the gate oxide using an ultra-high vacuum chemical vapor deposition technique. The i-Si_1-xGe_x serves as the channel while the i-Si is used as a buffer layer for allowing p⁺-Si_1-yGe_y to be etched selectively on. p-channel thin-film transistors with a field-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-Si_1-xGe_x/poly-Si multilayer structure would be a promising way for polycrystalline thin-film device applications.