Received 31 July 2015; revised 5 November 2015; accepted 15
December 2015
Some 50 years ago discussions of plasmonics
in semiconductors lead to many new concepts such as travelling
domain structures with applications leading even to logic
systems. Now plasmonics of submicron wires of Ag and graphene
bring new device concepts for the fabrication of compact THz
sources and optical focusing of the beat signal into the
active area. Here as an experimental example such new
opportunities are involved with compact THz sources based on
optical laser mixing. They include resonant plasmonic
structures at THz and optical frequencies to locally enhance
the electromagnetic fields at THz as well as optical
frequencies by the combination of semiconductor-graphene
plasmons respectively by the semiconductor-metal-nanostructure
plasmons.
Of particular interest is the usage of graphene, which is
optically transmitting and which is either a semimetal or can
be transformed into a semiconductor by reducing the width of
its strips to about 30 nm, opening a band gap in the meV to
tens of the meV range.
A successful experimental structure for continuous-wave THz
photomixing is fabricated using 1D and 2D nanocontacts either
on low-temperature-grown (LTG) GaAs or on nitrogen
ion-implanted (N+i) GaAs and graphene sheets. The overlaying
1D and 2D nanocontacts were formed by silver nanowires with a
diameter of 60 or 120 nm. They can handle currents of >10
and >30 mA, respectively, without electromigration enabling
reliably high photocurrents and field enhancement at THz
frequencies by plasmonic effects.
The nanomaterial structurization in connection with
present-day plasmonic applications is now to be discussed in a
similar manner as past opportunities with semiconductor
plasmonics.
Keywords: collective
excitations, radiowave and microwave technology, nanowires,
electronic transport in graphene
PACS: 73.20.Mf,
84.40.-x, 62.23.Hj, 72.80.Vp
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