Optoelectronic properties of Ta$_3$N$_5$: A joint theoretical and experimental study*

A joint theoretical and experimental study of the optoelectronic properties of Ta$_3$N$_5$ was conducted by means of ab initio calculations and ellipsometry measurements [1]. Previous experimental work on Ta$_3$N$_5$ has not been conclusive regarding the direct or indirect nature of light absorption. Our work found excellent agreement between the optical spectrum computed using the Bethe-Salpeter equation and the measured one, with two prominent features occurring at 2.1 and 2.5 eV assigned to direct transitions between N and Ta states. The computed optical gap, obtained from the $G_0W_0$ direct photoemission gap, including spin-orbit coupling, electron-phonon interaction, and exciton binding energy, was found to be in excellent agreement with measurements. Our results also showed that Ta$_3$N$_5$ is a highly anisotropic material with heavy holes in several directions, suggesting low hole mobilities, consistent with low measured photocurrents in the Ta$_3$N$_5$ literature. Work is in progress to compute polaronic contributions to the hole and electron mobilities and to investigate the effect of substitutional doping on the electronic structure of Ta$_3$N$_5$.\\[4pt] [1] Juliana M. Morbec, Ieva Narkeviciute, Thomas F. Jaramillo, and Giulia Galli, Phys. Rev. B 90, 155204 (2014).