Optoelectronic devices based on the group-III nitrides are the only commercially available solution in the green to violet part of the visible spectrum and have a wide array of applications: white nitride LEDs can potentially replace incandescent and fluorescent light bulbs for general illumination, and nitride lasers, already used for high-density optical storage, can be employed in portable laser projectors. However, large internal losses limit the high-power performance of these devices. The internal quantum efficiency of nitride LEDs drops significantly when operating at high injected-carrier densities (the so-called "efficiency droop" problem), while large internal absorption losses limit the light-output power of nitride lasers.
We developed a set of first-principles computational approaches, based on density functional and many-body perturbation theory, to identify the microscopic mechanisms responsible for the efficiency reduction in nitride optoelectronic devices. We found that the efficiency droop of nitride LEDs can be attributed to indirect Auger recombination processes, mediated by electron-phonon coupling and alloy scattering. Moreover, we show that the absorption loss in nitride lasers is due to the internal reabsorption of the generated light by free and acceptor-bound carriers in the active region and adjacent n- and p-type layers. Our work suggests ways to overcome the efficiency issues in nitride optoelectronic devices and illustrates the significance of first-principles calculations in materials research.