Semiconductor-Semiconductor

Thermopiles are considered temperature sensors and are fabricated incorporating a number of thermocouples. Each thermocouple is formed by a couple of different materials (Metall-Metal2, Metal-Semiconductor, Semiconductor-Semiconductor) and responds to a temperature difference localized between the two junctions (cold junction and warm junction ), see fig. 11. One of the two junctions can be considered the reference one. 

One frequently examined interface is the solid-liquid interface, where the solid phase may be a dielectric, a semiconductor, or a metal. Species located at these interfaces are of primary importance in electtochemisny and in chemistry of surface-active substances (surfactants). Another common type of interface is the solid-solid interface, specifically dielectric-dielectric, dielectric-semiconductor, dielectric-metal, semiconductor-semiconductor, semiconductor-metal, and metal-metal interfaces. These structures have an extremely important role in such areas as microelectronics and the chemistry of composites. Furthermore, positioning an ultrathin film at the interface of two media, one can substantially increase surface sensitivity of all IR spectroscopic methods. 

The term photovoltaic effect is further used to denote non-electrochemical photoprocesses in solid-state metal/semiconductor interfaces (Schottky barrier contacts) and semiconductor/semiconductor pin) junctions. Analogously, the term photogalvanic effect is used more generally to denote any photoexcitation of the d.c. current in a material (e.g. in solid ferroelectrics). Although confusion is not usual, electrochemical reactions initiated by light absorption in electrolyte solutions should be termed electrochemical photogalvanic effect , and reactions at photoexcited semiconductor electodes electrochemical photovoltaic effect . 

Solid-solid contact (inc. solid breakup) Metal to metal Metal to semiconductor Semiconductor to semiconductor Volta potential (equalization of Fermi levels) Electrolytic potential (where adsorbed water films may be present)... 

The National Technology Roadmap for Semiconductors, Semiconductor Industry Association, 1994. 

After discussing semiconductor/metal heterostructures let us now consider the case of semiconductor/semiconductor heterojunchons. The semiconductors will be characterized by the band gaps fg and E, where we arbitrarily assume that E > E, and with valence-HOMO band offset A v, dehned as the difference between VBM and HOMO, and the conduction-LUMO band offset A c, dehned as the difference between CBM and LUMO (see Fig. 4.28). Both AE v and AE c are dehned as posihve. 

Structural information on the atomic arrangements at the early stage of formation of metal-metal, metal-semiconductor interfaces and semiconductor-semiconductor heterojunctions is needed along with the determination of the structure of the electron states in order to put on a complete experimental ground the discussion of the formation of solid-solid junctions. Amongst the structural tools that have been applied to the interface formation problem Surface-EXAFS is probably the best... 

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