Enhancement of electrical conductance for pentacene thin film transistor by controlling an initial layer-by-layer growth mode directly on SiO₂ insulator

Initial nucleation and growth of pentacene films on various pre-cleaning treated SiO2 gate insulators were systematically examined by atomic force microscope. The performance of fabricated pentacene thin film transistor devices was found to be highly related to the initial film growth modes. In contrast to the film in the three-dimensional island-like growth mode on SiO₂ under an organic cleaning process, a layer-by-layer initial growth mode occurred on the SiO₂ insulator cleaned with ammonia solution which has shown much improved electrical properties of the thin film transistors. Field effect mobility of the thin film transistor devices could be achieved as high as 1.0cm² V^-1 s^-1 on the bared SiO₂/Si substrate and the on/off ratio was over 10⁶. The enhanced electrical conductance was further confirmed by an electrostatic force microscopic observation of quantized electrical potentials via charge-injection to the submonolayer pentacene islands with layer-by-layer growth mode.