Photon recycling in Ga1−<i>x</i>Al<i>x</i>As : Si graded-band-gap LED’s

Abstract

It is shown in this study that photon recycling, i.e., photoluminescence resulting from the self-absorption of photons generated by prior luminescence processes, affects the steady-state characteristics of graded-band-gap Ga1−xAlxAs : Si LED’s strongly and of constant-band-gap GaAs : Si LED’s weakly. In Ga1−x Alx As : Si, where the internal quantum efficiency is near unity, photon recycling can enhance the external quantum efficiency (ηext) by 25% or more. Moreover, the effective minority-carrier diffusion length (L) can be augmented by ∼40%. On the other hand, because the internal quantum efficiency in GaAs : Si is considerably less than 100%, the effect of photon recycling on η and L is less pronounced. A theoretical model of photon recycling in both the graded- and constant-band-gap material is formulated and its predictions for the effects on the external quantum efficiency, the diffusion length, and the electroluminescent spectrum are in good agreement with the experimental results.