Semiconductor-metal contacts

The growth of solid films onto solid substrates allows for the production of artificial stmctures that can be used for many purposes. For example, film growth is used to create pn junctions and metal-semiconductor contacts during semiconductor manufacture, and to produce catalytic surfaces with properties that are not found in any single material. Lubrication can be applied to solid surfaces by the appropriate growth of a solid lubricating film. Film growth is also... 

T. Ioannides, and X.E. Verykios, Charge transfer in metal catalysts supported on Doped Ti02 A Theoretical approach based on metal-semiconductor contact theory, J. Catal. 161,560-569 (1996). 

The photovoltage is esentially determined by the ratio of the photo- and saturation current. Since io oomrs as a pre-exponential factor in Eq. 1 it determines also the dark current. Actually this is the main reason that it limits the photovoltage via Eq. 2, The value of io depends on the mechanism of charge transfer at the interface under forward bias and is normally different for a pn-junction and a metal-semiconductor contact. In the first case electrons are injected into the p-region and holes into the n-region. These minority carriers recombine somewhere in the bulk as illustrated in Fig. 1 c. In such a minority carrier device the forward current is essentially determined... 

In this context it should be mentioned that the height of the Schottky barrier depends on the proc iure of metal deposition and also on the pretreatment. Aspnes and Heller have investigated for instance metal-semiconductor contacts produced by depositing Ru, Rh or Pt as 400 A thick films. They found barrier heights for the metal in contact with air, of 0.6 eV for Ru on Ti02, which decreased to zero in the presence of hydrogen. These results are consistent with those of Yamamoto et al. . ... 

To further substantiate the proposed model, they have carried out some investigations connected with modification of semiconductor electron subsystem [174, 175]. Temperature is one of the important factors. Having no effect on the electron emission from the metal under the action of RGMAs, temperature strongly affects the current-transfer processes at the metal - semiconductor contacts. The impact of temperature on the interaction of RGMAs with Au/ZnO structures can be evaluated as follows. 

E.Kh. Roderik, Kontakty Metall - Poluprovodnik (Metal-Semiconductor Contacts), Moscow Radio i Svyaz , 1982, 206 p. 

John A. Copeland and Stephen Knight, Applications Utilizing Bulk Negative Resistance F.A. Padovani, The Voltage-Current Characteristics of Metal-Semiconductor Contacts P.L. Hower, W.W. Hooper, B.R. Cairns, R.D. Fairman, and D.A. Tremere, The GaAs Field-Effect Transistor Marvin H. White, MOS Transistors... 

A piece of silicon immersed in an electrolyte behaves similarly to a Schottky diode, a metal-semiconductor contact, as discussed in Chapter 3. Under reverse... 

As with metal-semiconductor contacts, the electric field in the space charge, which is given by the diffusion voltage Fd and the width of the space-charge region W, separates optically generated electron-hole pairs. W is given by 41> ... 

F. A. Padovani, The Voltage-Current Characteristics of Metal-Semiconductor Contacts... 

The atomic geometry of a surface or interface is, in certain respects, its most fundamental property. Since most surfaces and interfaces are metastable, especially those of technological interest, their composition and structure depends on their process history. Their structures determine, moreover, the "interesting" interfacial properties which are utilized in specific applications, e.g., reactivity and specificity in catalysis or Schottky barrier height in metal-semiconductor contacts. In addition, the interface structure is measurable by one or more of the techniques noted earlier. Therefore the structure of an interface is a measurable link between the process used to prepare it and the electronic and chemical properties which determine its utility. 

E. H. Roderick and R. H. Williams, Metal-Semiconductor Contacts, 2nd Edition (Clarendon Press, Oxford, 1988). 

As a result, nearly perfect interfaces between the ferromagnetic material and the semiconductor are not a prerequisite for efficient spin injection. It is for example possible to insert a non-magnetic seed layer between the ferromagnetic base layer and the semiconductor collector. Since hot electrons retain their spin moment while traversing the thin non-magnetic layer this will not drastically reduce the spin polarization of the injected current. Finally, since electron injection is ballistic in SVT and MTT devices the spin injection efficiency is not fundamentally limited by a substantial conductivity mismatch between metals and semiconductors [161, 162], The latter is the case in diffusive ferromagnetic metal/semiconductor contacts [163],... 

E.H. Rhoderick, R.H. Williams Metal-Semiconductor Contacts (Clarendon Press, Oxford 1988)... 

Refs. [i] Shockley W (1950) Electrons and holes in semiconductors. Van Nostrand, New York [ii] Blakemore JS (1987) Semiconductor statistics. Dover, New York [Hi] Rhoderick EH (1978) Metal-semiconductor contacts. Clarendon Press, Oxford [iv] Ashcroft W, Mermin ND (1976) Solid state physics. Saunders College, Philadelphia [v] SeegerK (1991) Semiconductor physics - an introduction. Springer, Berlin... 

Schottky contact — Alternative denomination of metal-semiconductor contact presenting a Schottky barrier. Depending on metal - work function, semiconductor electron affinity, doping of the semiconductor, conditions of the surface of the semiconductor before contact preparation, and preparation process, Schottky contacts with high rectification can be prepared. Devices encor-porating such contacts behave like a diode and for this reason, are also denominated Schottky diodes, whose main features are the capability of high frequency operations and low forward-voltage drop. 

Refs. [i] Mills I, Cvitas T, Homann K et al (eds) (1993) IUPAC quantities, units and symbols in physical chemistry. Blackwell Scientific, Cam-brigde, p 37 [ii] Parsons R (1974) Pure Appl Chem 37 503 [Hi] Bockris JO M, Khan SUM (1993) Surface electrochemistry. Plenum Press, New York, p 83 [iv] Fromhold Jr AT (1981) Quantum mechanics for applied physics and engineering. Academic Press, New York, 1981 [v] Lang ND, Kohn W (1971) Phys Rev B 3 1215 [vi] Rhoderick EH (1978) Metal-semiconductor contacts. Clarendon Press, Oxford [vii] Trasatti S (1986) Pure Appl Chem 58 955... 

Walter Haus Schottky (1886-1976) received his doctorate in physics under Max Planck from the Humboldt University in Berlin in 1912. Although his thesis was on the special theory of relativity, Schottky spent his life s work in the area of semiconductor physics. He alternated between industrial and academic positions in Germany for several years. He was with Siemens AG until 1919 and the University of Wurzburg from 1920 to 1923. From 1923 to 1927, Schottky was professor of theoretical physics at the University of Rostock. He rejoined Siemens in 1927, where he finished out his career. Schottky s inventions include the ribbon microphone, the superheterodyne radio receiver, and the tetrode vacuum tube. In 1929, he published Thermodynamik, a book on the thermodynamics of solids. Schottky and Wagner studied the statistical thermodynamics of point defect formation. The cation/anion vacancy pair in ionic solids is named the Schottky defect. In 1938, he produced a barrier layer theory to explain the rectifying behavior of metal-semiconductor contacts. Metal-semiconductor diodes are now called Schottky barrier diodes. 

The carrier effect is most easily considered for the case where the carrier is a semiconductor, since the dhscussion can be based on the Schottky theory (15,16) of metal-semiconductor contact, made familiar to catalytic chemists by its adaptation to explain depletive chemisorption on semiconductors (17. 

The results of Schwab s experiments indicate that there is a carrier effect whose direction can be correlated with predictions based on the metal-semiconductor contact theory. However in catalysis research there are many examples of cases where attempts to reproduce complicated experiments of this type have resulted in conflicting results. A question of this basic importance will need confirming evidence before the concept of the carrier effect is widely accepted. 

At metal/semiconductor contacts the cone angle 6=5° since tan e= Va/ Vf, with Ejt, is the thermal velocity of electrons (10 cm s ) and Vf is the velocity of electrons at the Fermi surface in the metal (10 cm s ) [189]. In BEEM 6 should be even smaller since ballistic electrons have a greater kinetic energy than electrons in the metal. 

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