Pulsed excitation of low-mobility light-emitting diodes: Implication for organic lasers

We present a theoretical and experimental study of electrical pulsed excita tion in polymer light-emitting diodes (LEDs). We find that the low mobility results in a relatively high charge density within an electrically pumped structure. The broad spectrum of the charge-induced absorption and its over lap with the ground-state absorption pose a significant barrier for achievi ng net gain and lasing. We suggest an approach that might circumvent this p roblem using suitable emitters and an appropriate driving scheme. We also s uggest methods for ultrafast modulation of LEDs as well as direct determina tion of the space charge within the recombination zone. (C) 1999 American I nstitute of Physics. [S0003-6951(99)05019-6].