  The quantum efficiency of AlGaN ultraviolet light-emitting diodes (LEDs)
declines (droops) at increasing operating powers due to Auger-Meitner
recombination (AMR). Using first-principles density-functional theory, we show
that indirect AMR mediated by electron-phonon coupling and alloy disorder can
induce bulk $C$ coefficients as large as $\sim10^{-31}$ cm$^6$/s. Furthermore,
we find that the confinement of carriers by polarization fields within quantum
wells severely relaxes crystal-momentum conservation, which exacerbates the
rate of AMR over radiative recombination by an order of magnitude relative to
the bulk. This results in a striking decrease in quantum efficiency at high
power. Suppressing polarization fields and jointly increasing the well width
would greatly mitigate AMR and efficiency droop.
