In this work, we report a novel method to achieve half-metallicity in silicene. Silicene is functionalized with Br-atoms to achieve half-metallicity. Both full-Br-silicene and half-Br-silicene are considered. Half-Br-silicene shows a half-metallic character, whereas full-Br-silicene has a semiconducting nature. Besides the half-metallic nature, half-Br-silicene is found to have a stable antiferromagnetic (AFM) configuration. The AFM nature of half-Br-silicene allows tuning the polarization of the spin-down and spin-up channels oppositely. Our proposed device based on the half-Br-silicene shows that the polarization of the carriers can be switched from spin-down to spin-up by using a lateral electric field. The proposed device can be used to implement higher-order spintronic circuits.