Ohmic Contacts to Gallium Aluminum Arsenide for High Temperature Applications

摘要

A new approach for fabricating nonalloyed ohmic contacts to gallium arsenide was developed. The approach uses ultrathin layers of heavily doped germanium or silicon in contact with gallium arsenide to alter the Schottky barrier height(phi B) at the gallium arsenide interface. For n-type gallium arsenide phi B could be varied from about 0.3 to 1.0 eV. The low barriers are useful for tunneling ohmic contacts to n-gallium arsenide while the high barriers should be useful for p-gallium arsenide ohmic contacts and for Field Effect Transistor (FET) gate applications. In some instances it was necessary to interpose a thin nonmetallic electrically conducting barrier between the contact metal and the thin germanium or silicon layer to preserve optimum contact properties. Specific contact resistivity measurements indicated that contact resistivity < 10 to the -6 ohms/sq.cm should be obtainable in practical contacts to heavily doped material. It is generally observed that phi B at most gallium arsenide interfaces is confined to a relatively narrow range presumably due to a large concentration of acceptor and donor states closely spaced in energy near midgap. The new approach for normalized ohmic contact fabrication suggests that these states can be saturated with carriers from the heavily doped germanium silicon so as to substantially modify phi B. The resulting contact phi B is virtually independent of contact metallization; the heterojunction band alignment characteristics at the germanium or silicon interface with gallium arsenide determine the phi B of the contact. (aw)