Very low activation energy for carrier generation of surface doped organic single crystals observed by Hall effects

Very low activation energy for hole generation reaching 5.7 meV to realize the ionization rate of 100% at room temperature by surface doping of molybdenum oxide on rubrene single crystals was observed from the temperature dependence of the hole concentration directly measured by the Hall effect. Hole mobility having band-conductive nature was maintained after surface doping. Very low activation energy can be explained by the overlap of shielded Coulomb potentials. By increasing the concentration of charge transfer states at the interface between the crystal and the dopant, high doping efficiency can be achieved.