Indium Phosphide Transferred Electron Devices for Millimetre Wave Applications

Details are given of the current development stage of CW indium phosphide transferred electron oscillators (TEOs) designed for mm-wave applications. The aims of low-noise, good reliability and thermal stability dictate the use of n+-n-n+ epitaxial material, details of which are given. Device fabrication is discussed with emphasis being placed upon the thermal and electrical parasitics inherent in the diode structure. The thermal problems caused by indium phosphide´s high threshold field (¿3 × GaAs) are overcome using a novel device geometry, which possesses both a low-thermal impedance and minimum skin effect losses. This technology has permitted CW operation of indium phosphide TEOs from 30 to 140 GHz with output powers and conversion efficiencies significantly better than those achieved from gallium arsenide. Spectrum analyser measurements show that, like gallium arsenide, indium phosphide TEOs exhibit quieter f.m. noise characteristics than similar frequency silicon Impatt oscillators.