Origin of strong Auger-Meitner recombination in AlGaN deep-ultraviolet emitters

The quantum efficiency of AlGaN-based deep-ultraviolet (DUV) light-emitting diodes lags severely behind its visible-light counterparts. Continued advancements in the synthesis and doping of AlGaN alloys are expected to reduce extrinsic losses, however the intrinsic energy-loss mechanisms in AlGaN are less well understood. Auger-Meitner recombination (AMR) is a non-radiative process involving the scattering of three carriers via the Coulomb interaction that causes the quantum efficiency of light emitters to decrease (droop) at high operating powers. The importance of this non-radiative-loss mechanism in AlGaN remains unclear, because its ultra-wide band gap makes it exceedingly difficult to simultaneously satisfy energy and crystal-momentum conservation for the direct AMR process. In this work, we develop and apply first-principles calculations based on density-functional theory to obtain mechanistic insights into the radiative and AMR processes in bulk AlGaN alloys and AlGaN quantum wells. We find that the additional momentum provided by electron-phonon coupling and alloy disorder lead to indirect AMR coefficients C in AlGaN that are as large as in InGaN (C ~ 10^-31 cm⁶/s), which is known to suffer from severe efficiency droop. Moreover, we find that quantum confinement introduces a new scattering channel that significantly exacerbates AMR in AlGaN quantum wells, leading to an enhancement of the C/B ratio (where the B coefficient quantifies the radiative recombination) by an order of magnitude relative to the bulk. We propose experimentally feasible approaches for removing disorder and minimizing quantum confinement to mitigate efficiency droop in AlGaN DUV emitters.