工藤 一浩

Organic light emitting transistors which are vertically combined with the organic static induction transistor and organic light emitting diode are fabricated and the device characteristics depending on the structure of gate electrode are investigated. By optimizing the layer thickness and the size of slit-type Al gate electrode, high luminance modulation by low gate voltage as high as 1 V are obtained. The organic light emitting transistor described here is a suitable element for flexible sheet displays. (c) 2004 Published by Elsevier B.V.

Grain morphology, crystal structure and transistor characteristics of pentacene films have been studied using molecular beam deposition under various conditions: growth temperature ranging from - 5 to 80 degreesC and growth rate from 0.15 to 2 nm/min. Grain morphologies observed with atomic force microscopy are categorized into five groups, which are summarized in a phase diagram. Above the growth temperature of 40 degreesC, many 'recessed regions' which extend independently of molecular steps are observed on the film surfaces. Carrier mobilities of the films estimated from transistor measurements are distributed from 1 x 10(-5) to 0.20 cm(2)/Vs. A comparative study between the structural and electrical results indicates that the mobility does not explicitly depend either on grain size or on specific grain morphology. Lamellar grains associated with flat-lying molecules among differently oriented grains, gaps between grains and the recessed regions are considered to restrict the overall carrier mobility. (C) 2004 Elsevier B.V. All rights reserved.

Ultraviolet photoelectron spectroscopy (UPS) of C-60 thin-film field-effect transistors was measured with biasing gate voltages. A time-dependent change in the electronic structure of the C-60 film was, observed during the UPS measurement, which has never been observed in a C-60 film grown on a conductive substrate. The change was attributed to the accelerated polymerization of C-60 by comparing the UPS with that of the photopolymerized C-60. The polymerization Was associated with the increase in the field-effect electron mobility. This result indicates that mobile carriers produce reactive radicals in organic semiconductors. (C) 2004 American Institute of Physics.