Transient Electroluminescence in the Light-Emitting Diodes of Poly(p-phenylene) Thin Film

We have studied the temporal response of the electroluminescence (EL) emission in the lightemitting diodes fabricated with a vacuum-deposited poly (p-phenylene) (PPP) thin lm as an emissive layer sandwiched between indium-tin-oxide (ITO) and Al electrodes. Upon application of a rectangular driving voltage with a forward bias, we observed a time delay between the onset of the bias voltage pulse and the EL emission. The EL time delay results from the charge carrier transport towards the recombination zone. Since the hole mobility is much larger than the electron mobility in PPP, the EL delay time is the transit time for holes in PPP thin films. The hole mobility is estimated to be 1 105 cm2/Vs in vacuum-deposited PPP films

Charge Carrier Tunneling in the Light-Emitting Diodes of Poly(p-phenylene) Thin Film

We have studied the temperature dependence of the current-voltage (I-V ) and the electroluminescence-voltage (EL-V ) characteristics in the blue light-emitting diodes of vacuumdeposited poly (p-phenylene) (PPP) thin lms in the temperature range between 14 and 290 K. The onset of the EL occurs at an electric eld of about 7107 V/m, independent of the thickness of the PPP layer. The I-V and EL-V dependences show very weak temperature dependences and t very well with the Fowler-Nordheim tunneling formula. The results suggest that charge carrier injection is a tunneling process through an energy barrier of about 0.60.8 eV in indium tin oxide (ITO)/PPP/Al devices.This work was supported by the Korea Science and Engineering Foundation (KOSEF) through the Quantum- Functional Semiconductor Research Center at Dongguk University