Transition from schottky limit to bardeen limit in the Schottky barrier formation of Al on n- and p-GaAs(110) interfaces

Schottky barrier formation at room temperature (RT) and low temperature (LT) is studied by photoemission. In the low Al coverage regime (from 0.001 to about 1 ML), it is found that, compared to RT pinning behavior, the n-GaAs(110) surface band bending is attenuated, while the p-GaAs(110) surface band bending is enhanced. This striking phenomenon indicates that, by lowering the substrate temperature, one reduces the disturbance of the GaAs(110) surface, and the surface Fermi level of the n- and p-GaAs (110) tends to go to the same position, the so-called Schottky limit that characterizes a perfect defect-free interface. However, and the coverage increases (up to 30 ML), a new mechanism (in the framework of the unified defect model, it is the formation of defect levels due to the energy released as the adsorbed Al atoms start to form clusters and replace Ga) associated with a disturbed surface becomes dominant. Thus, the LT Fermi level positions of n- and p-GaAs move towards the RT positions, the so-called Bardeen limit. This demonstrates that, by controlling the surface disturbance, one can modify the Schottky barrier formation process, going from the Schottky limit which does not have pinning centers to the Bardeen limit which suggests the existence of pinning centers