NANOSTRUCTURE GAAS SCHOTTKY DIODES FOR FAR-INFRARED HETERODYNE RECEIVERS

Recent advances in nanostructure fabrication technology have made possible the development of GaAs Schottky barrier diodes with sub-half micron diameters and epitaxial layers which are heavily doped and only several 10's of nanometers thick. In this paper we demonstrate that these diodes are exceptional mixer elements at THz frequencies. In particular, we have investigated the system noise temperature, mixer noise temperature, conversion loss and the required local oscillator (LO) power over the frequency range from 800 GHz to 2.5 THz. The effect of cryogenic cooling on diode performance was also investigated. Furthermore, it is shown that the optimum bias current for mixing is proportional to the LO frequency, as has recently been demonstrated for other diodes. The smallest diode investigated had an anode diameter of 0.25 mum and a zero bias capacitance of 0.25 fF. For this diode, it was shown that optimum mixing performance was achieved when 1300 electrons passed through the diode each LO cycle, regardless of frequency.