Ultrahigh speed graphene diode with reversible polarity

► Geometric diodes showing electrical asymmetry were formed from asymmetric graphene structures. ► The polarity of the electrical asymmetry is a function of carrier type. ► Carrier type and hence diode polarity reversed with shifting applied gate voltage. ► The graphene geometric diode operates at a frequency of at least 28 THz. ► The reversible diodes can be applied to ultra-high-speed digital memory and flip-flops.