Terahertz photomixing in low-temperature-grown GaAs

Low-temperature-grown (LTG) GaAs offers the combination of sub-picosecond photocarrier lifetime and high breakdown electric field (greater than 5 X 105 V/cm), and is grown in epitaxial films having excellent quality for microelectronic fabrication. A THz photoconductive mixer (photomixer) is formed on these films by patterning low- capacitance planar electrodes coupled to a coplanar antenna. The photomixer is conveniently pumped by two frequency-offset diode-laser beams focused on the exposed GaAs area between the electrodes. This paper summarizes the operational principles of the photomixer in contrast to a competing technique based on coherent three-wave photonic mixing. It then reviews different configurations of the photomixer as a laboratory tunable source for chemistry and metrology, and addresses some of the challenges in applying the photomixer as a local oscillator in portable spectroscopic and radiometric receivers.