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 ΦB of electrochemically formed n-GaAs/Au Schottky barriers is investigated as a function of deposition potential VD . Two potential regions can be distinguished: one in which ΦB is comparable to the value of the contacts made by evaporation and another one in which ΦB is higher. This is explained on the basis of a different surface composition of GaAs in the respective potential regions. At more positive VD , gold will be deposited upon a surface at which the Ga atoms are –O− terminated. This leads to the formation of a Auδ+–Oδ− dipole layer at the interface and hence to an increase in ΦB . At more negative VD , 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 ΦB will be lower. This interpretation is supported by results, obtained on n-GaAs/Ag Schottky barriers formed in solutions with different pH.