Terahertz electrical response of nanoscale three-branch junctions

Abstract

Ultrafast time-domain electro-optical characterization of the ballistic three-branch junctions (TBJs) has been performed to investigate their electrical response at terahertz (THz) frequencies. A TBJ rectifier consisting of two TBJs in parallel was placed in a coplanar waveguide (CPW) in which subpicosecond electrical pulses were generated by a photoconductive switch. A LiTaO3-based electro-optic transducer measured the waveform of the incident and transmitted voltage signals with a subpicosecond temporal resolution. This experimental configuration allowed the rectifier’s electrical response to be studied with a bandwidth of up to 1 THz. Detailed analysis of the TBJ rectifier and the photoconductive switch was performed in both the time domain and frequency domain. This analysis revealed poor coupling of the excitation signal into the rectifier because of a severe impedance mismatch between the rectifier and CPW as well as a parasitic capacitive coupling between the input and output ports of the rectifier. The poor coupling limited our ability to observe any substantial nonlinear response of the rectifier at THz frequencies. Possible solutions for enhancing the system bandwidth and efficient THz rectification are presented.