Heterojunction organic thin-film transistors

We have developed a unique organic transistor structure which enables us to realize both p-channel and n-channel operation in a single device. This device also demonstrates the applicability of heterojunction concepts to organic semiconductors. The active material consists of two layers: the first layer, typically 10-20 nm thick, is made up of /spl alpha/-hexathienylene (/spl alpha/-6T), a thiophene oligomer which exhibits good p-channel operation. The second active material is C/sub 60/ and is about 20-30 nm thick. The energy levels of the occupied and unoccupied molecular orbitals of /spl alpha/-6T and C/sub 60/ are such that when the gate is biased negatively with respect to the source, the p-channel material is filled with holes and when the gate is biased positively, the n-channel material (C/sub 60/) is filled with electrons. A detailed analysis of the transistor characteristics provides important insights into transport in organic materials and is discussed.