THz Solid-State Electronics

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