Deep saturation of junction voltage at large forward current of light-emitting diodes

The dependences of series resistance, ideality factor, and junction voltage of light-emitting diodes (LEDs) on applied voltage or current were characterized accurately using alternating current (ac) behavior combined with I-V plot (ac IV method). The deep saturation of junction voltage and simultaneous decrease of ideality factor of LEDs at large forward current, which imply the pinning of quasi-Fermi levels, were observed. Comparing with our recent study of the similar phenomenon of laser diodes, in which the junction voltage jumps abruptly to a saturated value at lasing threshold, the changes of junction voltage of LEDs are gradual. In addition, the decrease of series resistance with the increasing current and the negative capacitance effect of LEDs were also investigated.(C) 2007 American Institute of Physics.Physics, AppliedSCI(E)EI14ARTICLE9null10