Large-signal-modulation of high-efficiency light-emitting diodes for optical communication

The dynamic behavior of high-efficiency light-emitting diodes (LEDs) is inv estigated theoretically and experimentally. A detailed theoretical descript ion of the switch-on and switch-off transients of LEDs is derived. In the l imit of small-signal modulation, the well-established exponential behavior is obtained. However, in the case of high injection, which is easily reache d for thin active layer LEDs, the small-signal time constant is found to be up to a factor of two faster than the radiative recombination lifetime. Us ing such quantum-well LEDs, we have demonstrated optical data transfer,vith wide open eye diagrams at bit rates up to 2 Gbit/s, In addition, we have c ombined the use of thin active layers with the concept of surface-textured thin-film LEDs, which allow a significant improvement in the light extracti on efficiency. With LEDs operating at 0.5 Gbit/s and 1 Gbit/s, we have achi eved external quantum efficiencies of 36% and 29%, respectively.