From the Schottky–Mott Rule to Interface-Induced Gap States

This chapter discusses the theoretical approaches that have been proposed to explain the alignment of the band structures at semiconductor interfaces, ranging from the Schottky-Mott and the Anderson rule for Schottky contacts and heterostructures, respectively, to the concept of interface-induced gap states (IFIGS). IFIGS are derived from the complex band structure of semiconductors, and their basic parameters are their branch-point energy as well as their density of states and their decay length at this reference level. The barrier heights of Schottky contacts can be most easily understood by experimentally following the changes in the electronic properties of clean semiconductor surfaces due to the deposition of metal atoms up to the formation of thick overlayers. In particular, the observation of the adatom-induced shifts in core levels of the semiconductors shows that the interface dipole can be described by the difference in the electronegativities of metal and semiconductor.