1-D and 2-D Nanocontacts for Reliable and Efficient Terahertz Photomixers

Abstract

New types of continuous-wave (CW) terahertz (THz) photomixers were fabricated using 1-D and 2-D nanocontacts on low-temperature-grown (LTG) GaAs as well as nitrogen-ion-implanted $({\rm N}^{+}{\rm i})$ GaAs. The 1-D and 2-D nanocontacts were formed by silver nanowires and graphene sheets, respectively. A silver nanowire (Ag-NW) with a physical diameter of $\varnothing \hbox{60 nm}$ and $\varnothing \hbox{120 nm}$ can handle currents of $>\! \hbox{10}$ and $>\! \hbox{30 mA}$ , respectively, without electromigration, thus enabling reliable high photocurrents. The small diameter of such a nanowire electrode in 1-D photomixers reduces the device capacitance by a factor of more than ten compared with photomixers with conventional interdigital fingers. Thus, these nanowire properties can be used for the fabrication of photomixers with cut-off frequencies $>\hbox{2 THz}$ and with extremely reliable operation. A multilayer graphene (MLG) of 6–8 layers shows unique properties with high short-circuit current capabilities of $>\hbox{9 mA/(10}~\mu \hbox{m width})$ and reliable high photocurrents. Furthermore, the MLG absorbs only 2.3% of white light and is ideal as a transparent nanocontact. The use of these graphene electrodes in 2-D photomixers allows an efficient optical power illumination for high photocurrent generation and shows the potential for reliable CW THz emission. Initial THz measurements confirmed the high possibilities of these new nanocontact photomixers.