Phenomenology of metal-semiconductor electrical barriers

The phenomenological rules governing the values of electrical barriers between metals, and semiconductors or insulators are reviewed. The barrier energies on ionic insulators are shown to vary strongly with metal electronegativity, while in the case of covalent semiconductors, the barrier energies are relatively independent of the metal. The barrier energy from the metal Fermi level to the conduction band of the semiconductor is shown to be approximately two thirds of the semiconductor band gap with certain exceptions. The success of a simple barrier model in accounting for the properties of the barrier are reviewed. The variation of barrier energy with electrical field is reported for Al-SiO2, Al-GaSe, and Al-GaAs and compared with simple theory including image-force lowering and field penetration into the metal. Transport through interfacial barriers is illustrated by discussing transport through metal-GaSe-metal structures and metal-InAs Schottky barriers.