Effect of feedback carrier excitation on LED external quantum efficiency

Self-absorption of photons generated by prior luminescence processes affects both the steady-state and transient characteristics of LEDs. In this study we confine ourselves to one of the most important steadystate parameters-external quantum efficiency. It is shown that the photon self-absorption increases the injected carrier concentration, and consequently the emitted photon flux. This results in an increase in LED external quantum efficiency. A detailed analysis of this phenomenon is presented, and a simplified evaluation of its influence on the external quantum efficiency is given. Our calculation also takes into account multiple internal reflection of light generated inside the LED. The obtained results are applied to a diffused GaAs (Zn, Te) surface-emitting LED. It is estimated that the feedback carrier excitation (re-excitation) due to selfabsorption increases the LED external quantum efficiency by about 60% and multiple internal reflections by about 12%.