Currently, the terahertz and sub-terahertz frequencies provide excellent prospects for applications in medical, security, atmospheric and environmental monitoring as well as in ultra high speed telecommunication.
The resonant tunneling diode (RTD) is the ultimate high frequency electron devices due to its relatively simple structure and ease of processing. This diode exhibits negative differential resistance (NDR) with the ability to generate continuous wave (CW) at terahertz frequency when integrated with oscillator circuit.
In its simplest form, the RTD consists of an undoped quantum well sandwiched between two undoped layer of barriers meanwhile both the emitter and collector contacts are heavily doped. This research focuses material growth, device processing techniques, electrical characterisation and the realisation of an integrated InGaAs/AlAs RTD oscillator.
To ensure low power consumption of the device, the peak voltage is engineered to be as low as possible through the use of a highly strained, high indium-content (80%) quantum well.
The processing technique poses some great challenges as well. As a rule of thumb, any high frequency devices need a very small lateral area in order to reduce the device geometrical capacitance. The ability to define sub-micrometer lateral dimension by using only optical lithography, thanks to our newly developed low temperature trilayer soft-reflow technique is one novelty of this research.