Surface potentials on Pd/GaAs contacts studied using scanning probe microscopy

Abstract

Two Pd=GaAs contacts annealed at different tem- peratures were evaluated with the current-voltage measure- ment to be Schottky and ohmic contacts, respectively. Using a scanning probe microscope that is capable of surface po- tential measurement, we measured the contact potential dif- ferences (CPDs) for the Pd=GaAs Schottky contact and con- firmed that there is no significant potential barrier for the Pd=GaAs ohmic contact interface. By defining the ohmic electrode on the rear side of the GaAs substrate to be the ref- erence electrode, we observed that the surface potential on the GaAs surface is almost constant and attributed this tentatively to be a result of the CPD between the probe tip and GaAs surface. SPM technique for measuring CPDs, we prepared both Schot- tky and ohmic Pd=GaAs contacts whose electrical properties (barrier heights) were evaluated with I- V measurements. We have shown a comparison of the surface potential dif- ference between the Pd film and GaAs substrate measured using the SPM technique with the barrier height estimated from the I- V method (4). In this article we propose to per- form quantitative analysis on the surface potential, by defin- ing the ohmic electrode prepared on the rear side of the GaAs substrate as the reference electrode. We prepared two types of Pd=GaAs interfaces by annealing at different temperatures and evaluated them with the I- V measurements to be Schot- tky and ohmic contacts. We measured surface potentials on the Pd film and GaAs substrate surface for these two types of Pd=GaAs interfaces. We obtained unique information useful for the explanation of the surface potentials measured using the SPM and confirmed that there is no significant potential barrier at an ohmic contact of Pd on GaAs.