  For nitride-based InGaN and AlGaN quantum well (QW) LEDs, the potential
fluctuations caused by natural alloy disorders limit the lateral intra-QW
carrier diffusion length and current spreading. The diffusion length mainly
impacts the overall LED efficiency through sidewall nonradiative recombination,
especially for $\mu$LEDs. In this paper, we study the carrier lateral diffusion
length for nitride-based green, blue, and ultraviolet C (UVC) QWs in three
dimensions. We solve the Poisson and drift-diffusion equations in the framework
of localization landscape theory. The full three-dimensional model includes the
effects of random alloy composition fluctuations and electric fields in the
QWs. The dependence of the minority carrier diffusion length on the majority
carrier density is studied with a full three-dimensional model. The results
show that the diffusion length is limited by the potential fluctuations and the
recombination rate, the latter being controlled by the polarization-induced
electric field in the QWs and by the screening of the internal electric fields
by carriers.
