Ge/GaAs heterojunction IMPATT's

The fabrication and first successful operation of Ge/GaAs heterojunction IMPATT's are described. Theoretical analyses were employed to establish the optimum materials specifications for maximum microwave performance. The analyses revealed that the heterojunction IMPATT's should be inherently more producible than the conventional Read-type GaAs structures because their efficiencies should be less dependent on critical control of the avalanche region width. On the other hand, the maximum conversion efficiencies of both structures should be similar. Since the potential for detrimental effects due to solid-state diffusion of species across the Ge/GaAs interface increases strongly with temperature, development of special low-temperature fabrication processes was required for the heterojunction devices. The Ge epitaxial avalanche layers were deposited on the GaAs portions of the structures by vapor phase epitaxy at 325°C using an open-tube iodide-transport process. Ion implantation and partial low-temperature annealing at 275°C were employed to produce p-n junctions in the Ge layers. Heterojunction IMPATT's were produced that yielded powers of 410 mW at 6.3-percent efficiency and 320 mW at 4.4-percent efficiency at 10.7 and 15.2 GHz, respectively. The conversion efficiencies are limited, in part, by residual implantation damage that could not be removed at the maximum permissible annealing temperatures.