Microcrystalline silicon with high electron field-effect mobility deposited at 230°C

We made top-gate n-channel thin-film transistors of directly deposited microcrystalline silicon (mu c-Si). The pc-Si films were grown by plasma-enhanced chemical vapor deposition (PECVD) at 230 degrees C, from a gas mixture of SiH4 and SiH2Cl2 under H-2 dilution. Deposition rates of greater than or equal to 1 Angstrom/s were obtained with a plasma excitation frequency of 80 MHz. The 1.2 mu m-thick films are microcrystalline with grains oriented along the [220] direction perpendicular to the glass substrates, A conductivity of 4 x 10(-5) (Omega cm)(-1) (300 K) and thermal activation energy of 0.25 eV are obtained for films with a concentration of bonded hydrogen of 4 at.%, and optical gap E-04 (E-03) of 2.0 (1.53) eV. Top-gate transistors were fabricated with the highest process temperature being 280 degrees C. We obtained devices (W/L = 180 mu m/45 mu m) with ON current similar to 100 mu A, ON/OFF current ratio of 10(4), and electron mobilities in the linear and saturated regimes 13 and 20 (+/-1) cm(2)/V s, respectively. (C) 2000 Published by Elsevier Science B.V. All rights reserved.