The Double-Barrier Quantum Well
(DBQW) RTD is considered as the most promising candidate for high-speed functional
devices and THz oscillators at room temperature. For THz oscillators, the highest
frequency of electronic single devices at room temperature reported recently (2016)
is 1.9THz holding much promise for the realisation of compact and efficient electronic
THz oscillators
The DBQW-RTD in its simplest form, consists of a few monolayers undoped quantum
well sandwiched between two undoped layer of barriers of thickness 3 monolayers.
The emitter and collector contact regions are heavily doped. One of the key
technologies for this achievement is the precise control of epitaxial growth of ultrathin
semiconductor heterostructures. The structural design of oscillators and
microfabrication technology are also crucial. To achieve oscillations in the terahertz
regime, this programme will examine a novel RTD structure designs with ultra thin
AlAs tensile barriers and highly compressive InGaAs quantum wells, which effectively
reduces both the operating bias voltage and electron transit time in the collector
depletion region. InGaAs/AlAs RTD oscillator with 0.9-nm-thick barriers will be
studied for fundamental oscillations at frequencies > 1 THz at room temperature. This
programme will examine the integration of RTDs with RF circuits to form complete
narrow band emitters in the THz region for use as high power emitters in CW THz
imaging systems.