A tunable terahertz resonator includes a semiconductor substrate and a metal layer contacting a surface of the semiconductor substrate. A depletion layer is formed in the semiconductor substrate near an interface between the metal layer and the semiconductor substrate. A chiral nanostructure is coupled to the substrate or the metal layer, the chiral nanostructure including a conducting or semiconducting material and having an inductance. A bias circuit applies a bias voltage across the metal layer and the semiconductor substrate to control a capacitance of a tunable capacitor that includes the depletion layer. The chiral nanostructure and the tunable capacitor form a tunable resonant circuit. The tunable terahertz resonator can be used in a terahertz radiation emitter or receiver.