Barrier heights of real Schottky contacts explained by metal-induced gap states and lateral inhomogeneities

Abstract
Most metal–semiconductor contacts are rectifying. For moderately doped semiconductors, the current transport across such Schottky contacts occurs by thermionic emission over the Schottky barrier. The current–voltage characteristics of real Schottky contacts are described by two fitting parameters that are the effective barrier heights ΦBeff and the ideality factors n. Due to lateral inhomogeneities of the barrier height, both parameters differ from one diode to another. However, their variations are correlated in that ΦBeff becomes smaller with increasing n. Extrapolations of such ΦBeff-versus-n plots to the corresponding image-force-controlled ideality factors nif give the barrier heights of laterally homogeneous contacts. They are then compared with the theoretical predictions for ideal Schottky contacts. Data of Si, GaN, GaAs, and CdTe Schottky contacts reveal that the continuum of metal-induced gap states is the fundamental mechanism that determines the barrier heights. However, there are additional b...