Time-domain analysis of mode competition in ZnO nanowire lasers in inhomogeneous environments

Zinc oxide (ZnO) nanowire lasers are increasingly integrated into complex optoelectronic devices as a source of coherent radiation. To enable the rational design of these devices, it is crucial to understand how both the nanowire resonator and its surrounding environment influence mode competition and the three-dimensional structure of lasing modes. Additionally, realistic models of the lasing process must account for transient gain dynamics. In order to investigate the impact of an inhomogeneous environment, composed of various materials and structures, on mode competition, we conducted Finite-Difference Time-Domain (FDTD) simulations of the dominant lasing modes in different ZnO nanowire laser configurations. Our model describes how key parameters such as nanowire diameter, length, and substrate choice affect the field distribution in the lasing regime. We show that metallic substrates support lasing in thin nanowires in two distinct coupling regimes. Furthermore, we show that metallic particles attached to the nanowire end facets as a result of established nanowire growth techniques significantly influence lasing threshold, field distribution and competition between counter-propagating modes. We show that attaching an aluminum particle at the end facet of a ZnO nanowire leads to a threshold reduction, a switching of the dominant lasing mode and a mono-directional power flow inside a large segment of the nanowire.