EVOLUTION OF THE MICROSTRUCTURE OF AU(ZN) METALLIZATION DURING FORMATION OF AN OHMIC CONTACT TO P-TYPE GAAS

Structural processes occurring in thin Au(Zn) metallization during the formation of ohmic contact to p-type GaAs have been investigated by X -rav diffraction. secondary-ion mass spectrometry, transmission electr on microscopy and high resolution electron microscopy. In order to exa mine the release of arsenic during thermal processing, a thin film col lector method was applied. Emphasis was placed on the particular role of each of metallization constituents during consecutive stages of the formation of an ohmic contact. Pure Zn was found to penetrate the nat ive oxide on GaAs surface and to form an ohmic contact after annealing at 220-degrees-C. The addition of Zn into the Au metallization suppre sses the thermally induced decomposition of GaAs and stabilizes the si ze of Au grains, forming the alpha3-AuZn phase. The most important asp ect of the GaAs Au reaction is the formation of Ga vacancies in the su bcontact region. They are required to form a low resistance ohmic cont act to p-type GaAs. since the specific resistance of the Au(Zn) contac t is one order of magnitude lower than that of the pure Zn contact.