The mechanisms of Schottky barrier pinning in III–V semiconductors: Criteria developed from microscopic (atomic level) and macroscopic experiments

For the sake of perspective, an overview is given of the development of concepts concerning the mechanism involved in Schottky barrier (SB) formation. Until about 1972 principally “macroscopic” data (e.g., I–V and C–V electrical measurements) were available. More recently “atomic” level microscopic tools have been increasingly applied experimentally to the problem of understanding SB formation. The most popular models for the III–V semiconductors are examined in terms of the metal:III–V chemistry including its correlation with barrier height and/or the effect of metal thickness. Experimentally it is found that, for most metals, the Schottky barrier pinning is completed with the deposition of less than a monolayer of metal. Most importantly, the Fermi level pinning position at these low metal coverages is found to correspond well with the SB height obtained from I–V measurements from carefully prepared samples with thicknesses of about 1000 Å. On the other hand, the metal:III–V chemistry appears to have little effect on the SB height. For example, four metals - Ag, Au, Cu, and Pd - have very different chemistry (varying from essentially no reaction for Ag to a very strong reaction for Pd); however, they give almost identical SB heights. After comparison of experimental data with various currently popular models, only a refined version of the united defect model is found consistent with the available data.