Electrochemical formation and properties of n-GaAs/Au and n-GaAs/Ag Schottky barriers: Influence of surface composition upon the barrier height

The barrier height Phi (B) of electrochemically formed n-GaAs/Au Schottky barriers is investigated as a function of deposition potential V-D. Two potential regions can be distinguished: one in which Phi (B) is comparable to the value of the contacts made by evaporation and another one in which Phi (B) is higher. This is explained on the basis of a different surface composition of GaAs in the respective potential regions. At more positive V-D, gold will be deposited upon a surface at which the Ga atoms are -O- terminated. This leads to the formation of a Audelta+-Odelta- dipole layer at the interface and hence to an increase in Phi (B). At more negative V-D, metallic Ga will be formed during the cathodic decomposition of n-GaAs. As a consequence, surface Ga-O- groups will no longer be present, no surface dipole layers will be formed and Phi (B) will be lower. This interpretation is supported by results, obtained on n-GaAs/Ag Schottky barriers formed in solutions with different pH.