Ab Initio Radiative Lifetimes in Gallium Nitride

Wurtzite GaN is the primary semiconductor for efficient solid state lighting. The radiative recombination and excited carrier dynamics are challenging to measure in GaN due to the ultrafast (fs – ps) timescales at play and the presence of defects and interfaces in devices. Here, we present ab initio calculations of the radiative lifetime as a function of temperature in bulk GaN. We compute the exciton energies and wavefunctions using a combination density functional theory and GW-Bethe Salpeter equation (BSE) method. We derive an equation for the temperature dependent radiative lifetime for an anisotropic bulk crystal within the ab initio BSE framework. The radiative lifetimes in GaN obtained with this approach are in excellent agreement with experiment. We discuss the importance of including spin-orbit coupling, which, though weak in GaN, is essential to obtaining accurate radiative rates. Combined with our previous calculations of excited carrier relaxation in GaN [1], we can obtain from first principles key device parameters such as the hot carrier cooling time and the carrier diffusion lengths, with important technological implications.

[1] V. A. Jhalani, J.J. Zhou, and M. Bernardi. Nano Lett. 17, 5012 (2017).