Chemical trend of radiative recombination in III-nitrides

Since charge-carrier radiative recombination is a key process in semiconductors that enables light emission, it is critical to understand its chemical trend and microscopic mechanisms. Using III-nitride semiconductors as prototypical examples, we rigorously study the radiative recombination mechanisms employing first principles. We show that the radiative recombination coefficient is competitively impacted by the band gap, effective masses, and dipole matrix elements, but the band gap plays a dominant role. The radiative recombination coefficient is actually stronger in AlN, as compared to the ones in InN and GaN, despite the fact that AlN-based light-emitting diodes (LEDs) currently exhibit low efficiencies. However, the polarization direction of light emission in AlN is qualitatively different from those in InN and GaN due to valence-band reordering, which may lead to additional complication in light extraction. Our insights pave the way to optimize the optoelectronic performance of wide-band-gap LEDs.