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

Abstract

We made top-gate n-channel thin-film transistors of directly deposited microcrystalline silicon (μc-Si). The μc-Si films were grown by plasma-enhanced chemical vapor deposition (PECVD) at 230°C, from a gas mixture of SiH 4 and SiH 2Cl 2 under H 2 dilution. Deposition rates of ⩾1 Å/s were obtained with a plasma excitation frequency of 80 MHz. The 1.2 μm-thick films are microcrystalline with grains oriented along the [2 2 0] direction perpendicular to the glass substrates. A conductivity of 4 × 10 −5 (Ω 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°C. We obtained devices ( W/ L=180 μm/45 μm) with ON current ∼100 μA, 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.