Composite avalanche diode structures for increased power capability

The possibility of operating several avalanche oscillator wafers in parallel to obtain higher power and/or higher efficiency CW operation is explored analytically and experimentally. Experiments show that over a wide range the efficiency is roughly proportional to the power density in the semiconductor. The power densities required for good efficiency are very high and cannot be achieved in large area junctions without an excessive temperature rise caused by the thermal spreading resistance of the heat-sink material. The scheme delineated herein considers small area wafers spaced sufficiently close electrically that they operate as a single avalanche oscillator whereas their physical separation permits essentially independent heat sinking. It has been found that, as expected, the efficiency for CW operation improves approximately inversely with the diode diameter whereas the power capability for a given size wafer increases directly with the number of such wafers employed. The relative merits of mounting diodes on copper and on diamond are discussed. Experimental work indicates that the present approach is capable of producing 10 to 15 watts CW at 14 GHz in a single oscillator with available silicon diodes.