The terahertz frequency range sits between the microwave and mid-infrared regions of the electromagnetic spectrum, but has long resisted exploitation owing to difficulties in fabricating convenient sources and detectors; terahertz radiation is too high in frequency to be generated by the electronic techniques used in mobile telephones, but too low in frequency to be produced by the optical techniques exploited in, for example, CD player lasers.
However, the last twenty years have witnessed a remarkable growth in the field owing to the development of innovative sources, detectors, and imaging systems—and in particular, the quantum cascade laser. These developments have enabled a wide range of imaging and spectroscopy studies in which the selective absorption or transmission of terahertz radiation has provided unique and fundamental information about the physical and chemical properties of materials in this relatively unexplored region of the spectrum. Recent commercial application of terahertz instrumentation is now finding application in the pharmaceutical and automotive industries, and in high-resolution fault isolation in semiconductor devices and 3D imaging of integrated circuits, inter alia. We are looking to support three postgraduate research projects, each addressing a complementary aspect of the terahertz field.
The quantum cascade laser is an intersubband laser fabricated by a sophisticated high vacuum semiconductor growth technique called molecular beam epitaxy. The lasers comprise a carefully designed layered superlattice structure, containing thousands of semiconductor layers, each of nanometre-scale thickness and each deposited with an atomic layer resolution. The terahertz quantum cascade laser was highlighted by the journal Nature Photonics as one of the top photonics breakthroughs in the last 50 years, and the Leeds group is internationally recognized to be leading in the growth and fabrication of these lasers, often working with international collaborators. This PhD project will optimize the growth of quantum cascade lasers to increase their output power, operating frequency range, frequency tuneability, and maximum operating temperature. It will also explore new materials systems for use as quantum cascade lasers and detectors, and for developing understanding of the physical properties of intersubband and heterostructure devices.
Funding covers the cost of tuition fees as well as a maintenance grant to match the standard Research Council rates (around £14,777 in session 2018/19). Funding duration is 3 years.