Ab Initio Radiative Lifetimes in Gallium Nitride

Wurtzite GaN is the primary semiconductor for efficient solid state lighting. Light emission in materials is regulated by the dynamics of excited carriers, which is not completely understood in GaN. In particular, due to the ultrafast (fs – ps) timescales at play and to the presence of defects and interfaces in devices, the intrinsic radiative recombination rate is challenging to measure in GaN. 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 the GW-Bethe Salpeter equation method. An equation for the ab initio temperature dependent radiative lifetime in a bulk crystal is derived using Fermi’s Golden rule and applied to GaN. Combined with previous first principles 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. "Ultrafast Hot Carrier Dynamics in GaN and its Impact on the Efficiency Droop." Nano Letters 17, 5012 (2017).