Ohmic contact formation during continuous heating of GaAs and GaP Shottky diodes

Changes in the current-voltage and capacitance-voltage characteristics of semiconductor-solid metal structures (GaAs-Ni and GaP-Au Schottky diodes) during continuous heating have been studied. It is shown that the rectifying contacts are transmuted into ohmic contacts at some temperature T-ohm. This transition precedes the possible formation of a recrystallized layer that is peculiar to conventional ohmic contacts. The transition temperature T-ohm is substantially lower than the melting point of the metal. The current-voltage characteristics of structures annealed at different temperatures T-ann and cooled to room temperature have been studied. It is shown that at some temperature T-ann lower than some critical temperature T-0 the structural properties remain virtually constant, that at T-ohm> T-ann> T-0 the structures remain rectifying but excess currents appear, and that at T-ann > T-ohm the structures become irreversibly ohmic. It is assumed that after chemical interaction between the metal and the surface layer of the semiconductor, the newly formed surface acquires properties that account for the ohmic characteristics of the metal-semiconductor contact. (C) 1998 American institute of Physics.