Low temperature poly-SixGe1−x deposited by reactive thermal CVD for thin film transistor application

We have prepared a highly silicon-rich polycrystalline silicon–germanium (poly-SixGe1−x, x=0.98) film at 450 °C by the reactive thermal chemical vapor deposition (RTCVD) from a gaseous mixture of disilane (Si2H6) and germanium tetrafluoride (GeF4) under He dilution. We fabricated inverted-staggered bottom-gate n-channel thin-film transistors (TFTs) with films of 200 nm thickness deposited directly on SiO2/Si substrates. The TFT characteristics are influenced by the grain size of the poly-SixGe1−x films and carrier mobility was increased significantly after hydrogenation. The fairly high mobility of 36 cm2/V s and a low threshold voltage of 1.8 V have been achieved in the TFT prepared with the film having the largest grain size of 100 nm. We discuss the effect of crystallinity and defects in the films in conjunction with the TFT characteristics.