Optimization of photomixers and antennas for continuous-wave terahertz emission

We have studied terahertz emission from interdigitated finger photomixers coupled to planar antenna structures. Using both pulsed and continuous-wave excitation, polarization measurements reveal that the antenna design dominates the properties of the radiated output at frequencies below 0.6 THz, while the efficiency at higher frequencies is additionally dependent on the design of the photomixer fingers. We have produced terahertz maps of the device, characterizing the photomixer by measuring the generated power as a function of the excitation position. Together, these measurements have allowed us to understand better the distinct roles of the photomixer and antenna in emission at different fre

Comparative Study of Heterosturcture Barrier Diodes in the GaAs/AlGaAs System

Peer reviewedPublisher PD

High quality GaMnAs films grown with As dimers

We demonstrate that GaMnAs films grown with As2 have excellent structural, electrical and magnetic properties, comparable or better than similar films grown with As4. Using As2, a Curie temperature of 112K has been achieved, which is slightly higher than the best reported to date. More significantly, films showing metallic conduction have been obtained over a much wider range of Mn concentrations (from 1.5% to 8%) than has been reported for films grown with As4. The improved properties of the films grown with As2 are related to the lower concentration of antisite defects at the low growth temperatures employed.Comment: 8 pages, accepted for publication in J. Crystal Growt

Extremely uniform tunnel barriers for low-cost device manufacture

We report on the final steps needed to achieve the level of control over the properties of single tunnel barriers of AlAs needed to allow the manufacture of high-volume low-cost microwave and millimeter-waves detectors. We achieve a 1% standard deviation of the current–voltage characteristics across 2-in wafers and average currents from different wafers varying by 1%, when modeling shows that a monolayer error in the AlAs barrier layer thickness would result in a 270% change in the same electrical characteristics.This work was supported in part by the Engineering and Physical Science Research Council and in part by the Royal Society’s Mercer Innovation Award.This is the final version. It was first published by IEEE at http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=7097674

Miniaturized Folded Antenna with Improved Matching Characteristic for mm-wave Detections

UCMMT 2021 - UK-Europe-China Work. Millimetre-Waves Terahertz Technol., Sep. 2021UWIPOM2 project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 857654

Low-Cost Compact Integrated Rectenna for Implantable Medical Receivers

This work describes a novel fully integrated rectenna circuit using tunnelling-based devices for implanted medical devices. An ASPAT (Asymmetric Spacer Layer Tunnel Diode) was used as the active rectifier due to its high non-linearity and temperature insensitivity features. A miniaturized geometry rectenna ( 1×5 mm 2 ) with improved matching characteristics was demonstrated, by integrating a Cockcroft-Walton rectifier with an L-shaped planar folded antenna structure operating at ISM frequency bands. The circuit performance was experimentally explored at various separation distance between transmitter and receiver units. For a 5cm transmission set-up, the rectenna with a single-stage rectifier delivered 0.8V output at 20dBm transmit power. An extended doubler configuration exhibited enhanced performance when multiple stages are used, is predicted to reach 0.24mW output power at 23dBm transmit power and yielding ~1.6V output voltage with an efficiency of 0.12%. These findings can assist in compensating for the degraded antenna gain attributed to the extremely small effective-radiating area of 0.04λ . Furthermore, the ability of controlling the antenna input impedance helps in circumventing the requirement for a matching circuitry thereby offering further reduction in chip size.UWIPOM2 project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 857654