Characterisation of InGaAs/AlAs resonant-tunnelling diodes

Conference poster, 2024

Resonant-tunnelling diode (RTD) -based oscillators, capable of room-temperature fundamental oscillations up to 1.98 THz, show promise as terahertz sources. However, to cater for application requirements, there is a need for increased output power. A necessary step towards achieving this is the accurate characterisation of the RTDs. It is believed that this could further optimise the design of RTD-based oscillators, which is of great importance for achieving high output power at a predetermined frequency. The aim of this work is to accurately measure and characterise the small-signal behaviour of RTDs in the negative and positive differential region up to 1.1 THz.

The RTDs used consist of two thin layers of AlAs enveloping a layer of InGaAs. Spacer layers of undoped InGaAs encase the AlAs and serve to reduce the device capacitance. Two lightly doped regions supply the charge carriers, and lastly, two heavily doped regions enable the fabrication of ohmic contacts. With coplanar waveguides connected to GSG contact pads, vertical RTDs capable of both one- and two-port on-wafer S-parameter measurements are fabricated. De-embedding structures and multiline thru-reflect-line calibration standards are also designed and fabricated on-chip. A thin film resistor is fabricated in parallel to the RTD to enable measurements in the negative differential conductance region of the RTD. Measurements are performed with and without the shunt resistor, and after de-embedding of the resistor the results are compared. We will present preliminary results of extracting RTD model parameters.