Direct Electrical Measurements of Energy Bands in Organic Semiconductors by Device-Based Ballistic Carrier Emission Spectroscopy
Hyuk-Jae Jang, Oleg A. Kirillov, John S. Suehle, Curt A. Richter
Understanding the electronic structure of organic/molecular semiconductors and the energetics at their interfaces with metals is critical for organic-based electronics applications. Here we demonstrate that the energetics at metal/molecule interfaces can be electrically measured by ballistic charge carrier (both electron and hole) emission spectroscopy with a single three- terminal device in real operation, thus providing us with direct information on the electronic structures of molecular semiconductors such as their energy bandgap. The energy distribution of electronic states in the molecular semiconductors tailing into their energy bandgap is well described by Lorentzian function in our measurements. In spin-polarized carrier injection measurements, we observe little or no magnetoresistance signal in our magnetic tunnel transistors which indicates that spin filtering effects strongly subside either at the metal/molecule interfaces or in the organic layers.