Hole transport in amorphous-crystalline-mixed and amorphous pentacene thin-film transistors

We report on the hole transport behavior in amorphous-crystalline-mixed and amorphous pentacene thin-film transistors. Five organic thin-film transistors (OTFTs) were fabricated by evaporating the pentacene films at rates of 1, 3, 5, and 7 Angstrom/s at 25 degreesC (RT), and 7 Angstrom/s at 60 degreesC. The field-effect mobility increased with the deposition rate even though the crystalline quality of the pentacene film degraded from an amorphous-crystalline-mixed phase to an amorphous phase. With our optimum deposition rate of 5 Angstrom/s at RT, we obtained a saturation current (ID-SAT) of about 4 muA at a gate bias of -40 V, the field-effect mobility of 0.1 cm(2)/V s, and the on/off current ratio of 10(5). For the OTFT prepared with a deposition rate of 7 Angstrom/s at 60 degreesC, an amorphous pentacene channel layer with a high mobility of similar to0.3 cm2/V s and the on/off current ratio of 10(4) were observed. (C) 2002 American Institute of Physics.