We propose a simple quantum structure which exhibits resonant tunneling under one bias and simple tunneling under the opposite one, thus acting as a rectifier. The diode consists of a single laterally-indented barrier. Due to its particular conduction-band profile, electrons undergo resonant tunneling when the bias creates a band-profile triangular well which can contain a resonant state aligned to the emitter Fermi energy. A diode with an active layer of approximate to 100 Angstrom, realized by AlGaAs/GaAs, has a Rectification Ratio, calculated at the current-peak bias at resonance, of approximate to 100. This value can be enhanced by putting in series several elements of this kind. (C) 1995 Academic Press Limited