An epitaxial growth system comprises a housing around an epitaxial growth chamber. A substrate support is located within the growth chamber. A gallium source introduces gallium into the growth chamber and directs the gallium towards the substrate. An activated nitrogen source introduces activated nitrogen into the growth chamber and directs the activated nitrogen towards the substrate. The activated nitrogen comprises ionic nitrogen species and atomic nitrogen species. An external magnet and/or an exit aperture control the amount of atomic nitrogen species and ionic nitrogen species reaching the substrate.