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Overview:
The terahertz range – which lies between the frequency
ranges of electronic and photonic devices – is often
referred to as the "terahertz gap" because of the
lack of both high-power, low-cost, portable room temperature
THz radiation sources and efficient detectors to collect and
record those signals. This remains one of the most significant
limitations in modern terahertz systems.
The upper frequency limit of transistors
operating in conventional regimes is limited by the transit
time of carriers under the gate, for a field effect transistor,
or across the base and collector depletion region, for a bipolar
junction transistor. Scaling of feature sizes has pushed electronic
devices to operate at subterahertz speeds. However, in trying
to approach the terahertz range of frequencies, device feature
sizes approach values such that fundamental physics limitations
lead to diminishing returns on investment in further scaling
and transit time limitations. On the other hand, since the
quanta of terahertz radiation are much smaller than the thermal
energy at room or even at liquid nitrogen temperatures, photonic
devices using interband or intersubband transitions have to
operate at cryogenic temperatures. Plasma wave electronics
relies on propagation of surface plasma waves in the channel
of a field effect transistor. Typical plasma frequencies lie
in the terahertz range and do not involve any quantum transitions.
Therefore, using plasma wave excitation for detection and/or
generation of terahertz oscillations offers great promise.
Technical Description:
Plasma wave excitation in submicron field effect transistors
(FET) and related device structures should allow the THz electronics
lab to develop a new generation of solid-state terahertz tunable
devices that will support numerous applications in biotechnology,
microelectronics and defense.
Plasma waves are oscillations of electron
density in time and space. Shur's colleagues Dyakonov, Ryzhii,
Knap, Gaska, and Deng have shown that a short channel field
effect transistor has a resonance response to electromagnetic
radiation at the plasma oscillation frequencies of the two
dimensional electrons in the device. The devices, which use
this resonance response, should operate at much higher frequencies
than conventional transit-time limited devices – that
is, in the terahertz range – since the plasma waves propagate
much faster than electrons. Recently, Rensselaer researchers
reported on a resonant detector operating in the terahertz
range using an AlGaAs/GaAs 0.15 micron gate FET, offering
great encouragement that proposed improved structures are
indeed achievable.
Contact Information:
Michael Shur
Patricia W. and C. Sheldon Roberts '48 Professor of Solid
State Electronics
Professor, ECSE and Physics, Applied Physics and Astronomy
Director, Center for Broadband Data Transport Science and
Technology
Rensselaer Polytechnic Institute
110 8th Street
Troy, New York 12180-3590
(518) 276-2201
shurm@rpi.edu
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