Design and Characterization of In 0.22 Ga 0.78 As-Based Schottky-Barrier Diode Mixers Operating at 3.4 THz

A key challenge in developing terahertz Schottky-barrier diode-based receivers operating at ambient temperatures is to overcome the complexities of fabrication and machining, and to achieve efficient coupling between the waveguide feed horn and the THz signal. This paper presents characterization of WM-57, In0.22Ga0.78As Schottky-barrier diode mixers realized on a 2-μm-thick indium phosphide membrane. The mixers were pumped by a quantum-cascade laser operating at 3.4 THz; the radio and local-oscillator signals were spatially superimposed using a Mylar beam splitter and coupled to the mixers via an integrated pyramidal horn antenna. A double-sideband receiver noise temperature of 28 500 K was measured at 3.4 THz for 6-μm Mylar at an IF of 1.5 GHz, with 2-mW of LO power coupled to the mixer. The DSB receiver noise temperature corrected for atmospheric attenuation is 27 600 K. These results represent a key step toward room-temperature THz front-end systems for limb-sounding instruments to detect trace gases in the mesosphere and lower thermosphere of the Earth's atmosphere.