Rectifying metal—semiconductor contacts, semiconductor heterostructures, and semiconductor—insulator interfaces are most important concepts in semiconductor devices and circuits. When two solids are in contact and no intermixing occurs, their electronic structures will be perturbed locally at the interface since there the bonding configurations differ from those in the bulk of both materials. The alignment of the band structures at such contacts may be described in a simple model. It considers tailing of electron wavefunctions across the interface in the energy range where the metal conduction-band overlaps the band gap of the semiconductor or the valence band of one of the semiconductors overlaps the band gap of the other one. As surface states on clean and adatom-covered semiconductor surfaces, these metal-and semiconductor-induced gap states derive from the virtual gap states of the complex band structure of the respective semiconductor. Tailing of electron wavefunctions means charge transfer across the interface so that generally a dipole layer will exist at interfaces. The barrier heights in metal—semiconductor contacts as well as the band discontinuities at semiconductor heterostructures or semiconductor—insulator interfaces will contain dipole contributions. These scale with the electronegativities of the two solids in contact since the interface bonds are partly ionic. At real semiconductor interfaces, even if they are abrupt and epitaxial, fabrication-induced defects may be present. They will lead to variations of barrier heights in Schottky contacts, for example. Interfaces between two lattice-matched semiconductors will be distorted since the covalent radii of the constituent atoms are generally different. Such interface strain will have a marked influence on the actual band discontinuities at semiconductor heterostructures.
KeywordsBarrier Height Schottky Contact Interface Defect Semiconductor Heterostructures Interface Dipole
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