Molecular modification of an ionic semiconductor–metal interface: ZnO/molecule/Au diodes

Differences between junctions of metals on ionic or covalent semiconductors persist for junctions, prepared by wet solution methods with a molecular layer at the junctions’ interface. A series of molecules that controls the junction of Au with $\mathrm{n-}\mathrm{GaAs},$ does so even stronger with ZnO (300 instead of $\text{∼100\hspace{0.17em}}\mathrm{mV}$ barrier height change). With ZnO the interface behavior index is found to be 0.55, five times that with GaAs. This agrees remarkably well with results for junctions of these materials with different metals, prepared in ultrahigh vacuum. Thus, the free semiconductor surface, e.g., surface state density, rather than direct metal–semiconductor interactions, appears to dominate junction behavior.