Depletion organic semiconductors

Besides the transport properties, the contact formation between the source/drain electrodes and the organic semiconductor is crucial for the OFET performance. To illustrate this, balanced charge carrier transport properties ii = i2 in the above evaluated model are assumed and the injection of the complementary charge carrier species is hindered, e.g., by a pronounced injection barrier at the drain/semiconductor contact. The source contact is supposed to inject freely charge carriers of type 1 and out of simplicity they are assumed to be ejected freely at the drain electrode as well. For Vd —> IV g] the channel depletes more and more in the vicinity of the drain electrode and for Vg < Vd the charge carriers of type 1... 

Figure 13-4. Encigy level diagnim of a single-layer OLED, where the organic malerial is depicted as a fully depleted semiconductor. The valence band Ey corresponds to the HOMO and the conduction band Ec corresponds to the LUMO. Tile Fermi levels of the two metal electrodes are marked as Et-. Upon contact a built-in potential is established and needs to be compensated for, before the device will begin to operating.

Metal oxide semiconductor field-effect transistors (MOSFETs) are field effect transistors with a thin film of silicon dioxide between the gate electrode and the semiconductor. The charge on the silicon dioxide controls the size of the depletion zone in the polype semiconductor. MOSFETs are easier to mass produce and are used in integrated circuits and microprocessors for computers and in amplifiers for cassette players. Traditionally, transistors have been silicon based but a recent development is field-effect transistors based on organic materials. 

In early works, the reactivity associated widi TiO2 photocatalysis was assigned to free OH radicals, but more recently die oxidative species has been identified as bound HO radicals and photogenerated holes. Reaction of the substrate with these species would require either die direct adsorption of organic compounds to the semiconductor interface or Fickian diffusion of the substrate to the semiconductor surface under depletion conditions. However, these two pathways imply different mechanisms, and in some cases different reaction products or intermediates. 

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