POLYMER-BASED DEVICES THEIR FUNCTION AND CHARACTERIZATION

Electronic devices based on organic semiconductors, mainly conjugated polymers, have recently been reported. In this paper characterization and improvements of three devices will be presented, namely, Metal Oxide Semiconductor Field Effect Transistors (MOSFET), Schottky barrier diodes and Schottky gated Field Effect Transistors (MESFET). The MOSFET devices work through the modulation of an accumulation layer at the semiconductor (polymer)-insulator interface. A model for organic MOSFET is proposed by changing the classical equations according to this particular operating mode. It is shown that, the characteristics of these organic devices can be improved by controlling the doping in certain level and decreasing the thickness of the semiconducting (polymer) layer. The mobility also increases with the gate bias in contrast to inorganic semiconductor. A planar Schottky barrier diode is successfully fabricated and reported, using poly (3-alkylthiophene) as an active semiconductor and aluminium and gold electrodes are used as Schottky and ohmic contacts. The electrical characteristics of the poly (3-alkylthiophene)/metal interfaces have been studied. Electrical characterization reveals diode behaviour with a rectification ratios larger than 10(4) at sufficiently high voltage. The ideality factor (n) is as low 1.2. Possible transport mechanisms are discussed. In this paper also fabrication and characterization of Schottky gated planar field effect transistors using poly(3-alkylthiophene) as an active material am reported. Aluminium is used for the rectifying contact and two gold electrodes are used as source and drain. From the MESFET characteristic the channel carrier mobility is evaluated to be 10(-5) cm2/Vs, which is one order of magnitude larger than than mobility found from an MOS transistor using the same polymer.