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Electric potential distributions in space charge regions of molecular organic adsorbates using a simplified distributed states model
Author(s) -
Mankel Eric,
Hein Corinna,
Kühn Maybritt,
Mayer Thomas
Publication year - 2014
Publication title -
physica status solidi (a)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.532
H-Index - 104
eISSN - 1862-6319
pISSN - 1862-6300
DOI - 10.1002/pssa.201330432
Subject(s) - charge density , depletion region , surface states , space charge , semiconductor , schottky barrier , schottky diode , chemical physics , adsorption , electric potential , organic semiconductor , materials science , surface (topology) , work (physics) , density of states , work function , chemistry , condensed matter physics , nanotechnology , layer (electronics) , optoelectronics , physics , thermodynamics , voltage , quantum mechanics , mathematics , geometry , diode , electron
We study the evolution of the electric surface potential for small molecular organic semiconductors adsorbed on different high‐work function substrates using photoelectron spectroscopy. Usually, the surface potential of these materials shows a typical progression in dependence of the adsorbate layer thickness indicating the formation of a space charge region near the interface. We discuss the surface potential evolution on the basis of the commonly used Schottky model and a second model using a density of states distribution (DOS) in the adsorbed semiconductor energy gap. In order to derive an analytical solution, we simplify an existing approach for space charge regions at polymer contacts. This approach is based on tailing gap states in polymer adsorbates. We simplify it using a constant DOS distribution. The differences between the Schottky model and the simplified distributed states model will be discussed. Finally, both models are applied to measured values of the surface potential evolution of some exemplary organic molecules on different substrates. We find that the surface potential evolution of the simplified distributed states model describes the measured potential development more accurately than the Schottky model. The DOS is estimated in the framework of the model being between 10 18 and 10 19 cm −3 eV −1 .