Low resistance ohmic contacts to millimetre-wave graded gap Gunn diode oscillators

Low resistance ohmic contacts have been developed for state of the art graded gap Gunn diode oscillators for volume production of anti-collision/automatic cruise control car radar. Both alloyed and non-allowed contact schemes have been investigated. We report one of lowest specific contact resistivities to date for a conventional alloyed AuGeNiAu on n/sup +/-GaAs system and a non-alloyed TiAu on graded n-InGaAs on n/sup +/GaAs, of 1.03(/spl plusmn/0.7)/spl gamma//spl times/0.6/sup -2/ cm/sup -2/ and 1.07(/spl plusmn/0.7)/spl times/10/sup -7/ /spl Omega/ cm/sup -2/ respectively, achieved by incorporating very highly doped, high quality MBE grown epitaxial contact layers. The non-spiking nature of the non-allowed approach provides highly reproducible, consistently uniform resistivity ohmic contacts; an essential requirement for volume production processes when field and reliability are important. For such applications we highlight certain ill effects attributed to the alloying process, illustrated by measurements made on alloyed and non-alloyed GePd based contact systems.