Charge carrier tunneling in the light-emitting diodes of poly (p-phenylene) thin films

We have studied the temperature dependence of the current-voltage (I-V) and the electroluminescence-voltage (EL-V) characteristics in the blue light-e mitting diodes of vacuum-deposited poly (p-phenylene) (PPP) thin films in t he temperature range between 14 and 290 K. The onset of the EL occurs at an electric field of about 7x10(7) V/m, independent of the thickness of the P PP layer. The I-V and EL-V dependences show very weak temperature dependenc es and fit very well with the Fowler-Nordheim tunneling formula. The result s suggest that charge carrier injection is a tunneling process through an e nergy barrier of about 0.6 similar to 0.8 eV in indium tin oxide (ITO)/PPP/ Al devices.