Directional lasing in resonant semiconductor nanoantenna arrays

Directional lasing, with a low threshold and high quality factor, in active dielectric nanoantenna arrays is demonstrated. This is achieved through a leaky resonance excited in coupled gallium arsenide (GaAs) nanopillars. The leaky resonance is formed by partially breaking a bound state in the continuum (BIC) generated by the collective, vertical electric dipole resonances excited in the nanopillars for sub-diffractive arrays. By opening an unprotected, diffractive channel along one of the periods of the array one can control the directionality of the emitted light without sacrificing the high Q associated with the BIC mode, thus achieving directional lasing. A quality factor Q = 2750 is achieved at a controlled angle of emission of ~ 3 degrees with respect to the normal of the array with a pumping fluence as low as 10 uJ/cm^2. We demonstrate the possibility to control the lasing directivity and wavelength by changing the geometrical parameters of the nanoantenna array, and by tuning the gain spectrum of GaAs with temperature. Lasing action is demonstrated at different wavelengths and emission at different angles, which can be as large as 25 degrees to the normal. The obtained results provide guidelines for achieving surface emitting laser devices based on active dielectric nanoantennas that are compact and highly transparent.