Interface studies of organic thin film transistors

For both organic light emitting diodes and organic thin film transistors a better understanding of the physics that occur at the interfaces that are created in these devices would allow tailoring interfaces to improve performance. The majority of work examining these devices has focused on optimization of processing and device fabrication in order to improve the performance of these devices. Much less work has been performed directly measuring the electronic properties of the interfaces observed in organic thin film devices. The studies that have investigated the electronic properties of the material interfaces in these devices have shown the creation of interface dipoles, charge transfer, and chemical reactions at various interfaces. The understanding that these studies have provided have aided device design. Further work still needs to be performed to improve the understanding of the mechanisms involved in interface formation and the effect these mechanisms have on the electronic structure of the interface. In order to better the understanding of these interfaces I studied the interfaces formed between organic semiconductors and metals and dielectrics.; This thesis focuses on experiments that I have performed examining the electronic structure at interfaces between various organic materials and the metals and dielectrics used in organic thin film transistors. I examine the results of organic semiconductor deposition onto dielectric materials and show that these interfaces exhibit little change in the vacuum level, suggesting minimal charge interaction between organic and dielectric. I show that organic semiconductor deposition onto metal substrates along with the inverse situation where metal is deposited onto an organic semiconductor result in the formation of an electric dipole at the interface between the organic and metal, causing a shift of the vacuum level. The differences between the metal on organic and organic on metal depositions are discussed. I finish by examining the oxidation of a GaN surface and comparing it to the oxidation of a GaAs surface. I show that oxidation of a GaN surface results in a thin Ga oxide surface unlike the well-studied oxidation of a GaAs surface which results in a relatively thick layer of Ga and As oxides.