Development of high-performance Schottky diode detector in the submillimeter wave region

The aim of the research is to realize a high-performance Pt/GaAs Schottky Diode (SD) detector operated in the submillimeter wave (SMMW) region with characteristics of high-sensitivity and good mechanical stability. The detector consists of reverse honeycomb SD,whisker antenna and RF microstrip filter which are fabricated using photolithographic technique. Concerning a fabrication process of reverse honeycomb SD,we have successfully developed an ECR plasma anisotropic etching technique to make a dot-matrix pattern (diameter : 0.17mum, pitch : 0.5mum) on SiO_2 with thickness of 4000A without damaging the underlying GaAs epi-layr. This is essential to obtain low-noise SD and the technique would also be applicable to fabrication processes for other semiconductor devices. We also made the whisker antenna and RF microstrip filter and have verified their dimensions as designed. We plan to complete the reverse honeycomb SD,make the detector mount, assemble these components and then measure the detector characteristics.For the testing and characterization of the detector we have succeeded in developing an optically pumped SMMW laser with highly stable output power and a diplexer with propagation loss of 0.2dB.In the course of the development we have discovered a new lasing line (wavelength : 746.4mum) when using CH_2F_2 gas as a lasing media. We further tried to modulate the SMMW radiation by laser-produced free carriers in semiconductors. Modulation of 214.6mum radiation was carried out by irradiating high-resistivity silicon or GaAs wafers with optical pulses from a Nd : YAG laser. We have achieved SMMW switching with rise time of 6nsec and generation of SMMW short pulses with duration of 10nsec. This optical switching technique is very useful for measuring the speed of SMMW detectors and could be applied to fields like molecular spectroscopy and solid-state physics.