This research work concerns the characterisation, fabrication and testing of devices capable of generating and detecting terahertz (THz) radiation.
Such devices are based on semiconductor photoconductors grown at low temperatures using the technique of Molecular Beam Epitaxy. The absorption of a pulsed or continuous wave signal by these structures in conjunction with the presence of an electric field generates photocurrent, which is fed into an antenna structure fabricated on the surface of the active layers. As a result of such a sequence, a THz signal is generated and radiated from the substrate side into free space. The desired material characteristics are high absorption at the corresponding illumination wavelength, high dark resistivity, high electron mobility and sub picosecond carrier lifetime.
The design and fabrication of several antenna structures with various geometrical characteristics (Fig.1), and their evaluation as THz emitters and detectors in a time-domain spectroscopy system under pulsed excitation is undertaken. The biggest challenge in this work is the development of efficient devices operating at the telecom wavelength of 1.55 µm, which will allow a portable, low cost, THz spectrometer to be built. To this point, the key findings demonstrate photoconductors with excellent characteristics and system responses, which are among the best ever reported for such material systems. As a consequence, a compact, low cost, reconfigurable, fiber-based THz spectrometer at 1.55 µm was built in collaboration with our industrial partners (Fig.2).