Probing of electric field in pentacene using microscopic optical second harmonic generation

The electric field distribution in a pentacene field effect transistor (FET) was examined by using microscopic optical second harmonic generation (SHG) measurements. Results showed that the enhanced SHG signal changes depending on biasing conditions. The SHG profile was estimated by analyzing a Laplace field formed in organic FET (OFET) using conformal mapping and other methods. Results showed that the observed SHG profile is in good agreement with the obtained profile, indicating that our microscopic SHG data describe the electric field distribution in OFETs with high accuracy. The decrease in the SHG intensity was also discussed based on a Poisson field formation, caused by carriers injected from a source electrode. These results show that the SHG technique is effective for probing of electric fields formed in organic materials. (C) 2008 American Institute of Physics.