Trapped charge mapping in crystalline organic transistors by using scanning Kelvin probe force microscopy

Trapped charge distributions at the interfaces between gate insulators and crystalline organic semiconductors in thin-film transistors are visualized by using a technique based on scanning Kelvin probe force microscopy (SKFM). For the charge density measurement, an ac voltage is applied to the gate electrode and its amplitude is adjusted so as to keep the electrostatic force constant between the SKFM tip and the semiconductor surface. The trapped charge density shows characteristic spatial distributions in the channel region, which varies by voltage stresses applied to the transistors. By comparing the charge distributions with the surface-potential profiles, trap mechanisms are discussed.