Inhomogeneous and wide range of barrier heights at metal/molecular-beam epitaxy GaAs(100) interfaces observed with electrical measurements

Abstract

In situ internal photoemission, current–voltage, and capacitance–voltage measurements of electronic barrier heights at metal/molecular-beam epitaxy GaAs(100) interfaces indicate near-ideal behavior and large barrier heights for Au contacts but nonideal characteristics and barrier height inhomogeneity for Al contacts. The observed Au barrier heights of 0.98–1.10 eV are comparable among the three techniques employed and relatively uniform across the interface. Measurements indicate that Al barrier heights are laterally inhomogeneous. Analysis of internal photoemission results for the Al interface using a model of two parallel conduction channels yields good agreements with the experimental results. Fitting the model to the experimental results for different diodes prepared on the same surface yields a low electronic barrier of 0.37±0.05 eV and a high barrier of 0.72±0.04 eV. The former is consistent with our previous soft x-ray photoemission measurements and the latter agree with the value of reported Fermi-level ‘‘pinning.’’ In addition, the low barrier height increases with increasing duration of mechanical contact, indicating instability of the interface. Our results (1) confirm the wide range of barrier heights at metal/GaAs(100) interface observed previously, (2) demonstrate explicitly the existence of multiple contacts at metal/GaAs interfaces, and (3) suggest that differences in barrier heights in the literature are a direct result of local structural variation at the interface.