Semiconductors corrosion

It was learned that pitting-type metal and semiconductor corrosion is attended by the generation of noise seen in the form of dynamic irregularities in the changes of the anodic potential and current density. Thus, electrochemical noise studies were applied to the corrosion and passivation of metals and to their activation by external chemical (activating additives in the electrolyte) or electrochemical (anodic or cathodic polarization) agents. 

In the above argument, we only considered the electron-transfer reactions between the semiconductor surface and redox species in solution. Actually, the electrons and holes at the semiconductor surface often cause another type of redox reaction leading to semiconductor corrosion. For n-type semiconductors such as n-Si and n-GaAs, for example, the following anodic photo corrosion reactions occur.3,4)... 

A full description of photo-assisted semiconductor corrosion is not available. We have undertaken an analysis of this phenomena, relying on aqueous solution electrochemical equilibria considerations (16). 

There are other treatments of semiconductor corrosion, which have concentrated on different likely mechanisms. Tenne et al. have considered the case where the surface reactions may have chemical processes such as adsorption as rate-limiting reactions. Under these circumstances, the above treatment may be re-worked taking into account recombination [160]. 

Semiconductor corrosion will also be affected by the adsorption of ions and molecules on the semiconductors. We have nevertheless seen in the field of corrosion science almost no reliable research results on the catalytic characteristics of semiconductor corrosion. 

To improve the solar response of a photoelectrode, a proper match between the solar spectrum and the band gap of the semiconductor should be maintained. When a single band gap semiconductor is used, a band gap in the vicinity of 1.4 eV is most desirable from the standpoint of optimum solar-conversion efficiency. An important criterion is that the minority carrier that is driven toward the semiconductor-electrolyte interface should not participate in a photocorrosion reaction that is detrimental to the long-term stability of the photoelectrode. Photocorrosion can be viewed in terms of either kinetic or thermodynamic considerations and the real cause may be a mixture of both. From thermodynamic perspective, a photoanode is susceptible to corrosion if the fermi level for holes is at a positive potential with respective to the semiconductor corrosion potential [21]. The corrosion can be prevented or at least inhibited by choosing a redox couple that has its /ijedox more negative than that for the corrosion process [22,... 

Polyaniline has potential applications in areas such as organic semiconductors, corrosion inliibitors, color displays, energy storage devices, optoelectronic devices, and rechargeable pofymer batteries. This polymer has been endowed with desirable electrical, electrochemical, and optical properties coupled with excellent environmental stability [278-287]. 

The war itself also drove the development of improved and miniaturised electronic components for creating oscillators and amplifiers and, ultimately, semiconductors, which made practical the electronic systems needed in portable eddy current test instruments. The refinement of those systems continues to the present day and advances continue to be triggered by performance improvements of components and systems. In the same way that today s pocket calculator outperforms the large, hot room full of intercormected thermionic valves that I first saw in the 50 s, so it is with eddy current instrumentation. Today s handheld eddy current inspection instrument is a powerful tool which has the capability needed in a crack detector, corrosion detector, metal sorter, conductivity meter, coating thickness meter and so on. 

In corrosion, adsorbates react directly with the substrate atoms to fomi new chemical species. The products may desorb from the surface (volatilization reaction) or may remain adsorbed in fonning a corrosion layer. Corrosion reactions have many industrial applications, such as dry etching of semiconductor surfaces. An example of a volatilization reaction is the etching of Si by fluorine [43]. In this case, fluorine reacts with the Si surface to fonn SiF gas. Note that the crystallinity of the remaining surface is also severely disrupted by this reaction. An example of corrosion layer fonnation is the oxidation of Fe metal to fonn mst. In this case, none of the products are volatile, but the crystallinity of the surface is dismpted as the bulk oxide fonns. Corrosion and etching reactions are discussed in more detail in section A3.10 and section C2.9. 

Photoelectrochemistry may be used as an in situ teclmique for the characterization of surface films fonned on metal electrodes during corrosion. Analysis of the spectra allows the identification of semiconductor surface phases and the characterization of their thickness and electronic properties. 

It should be mentioned that as well as for metals the passivation of semiconductors (particularly on Si, GaAs, InP) is also a subject of intense investigation. However, the goal is mostly not the suppression of corrosion but either the fonnation of a dielectric layer that can be exploited for devices (MIS stmctures) or the minimization of interface states (dangling bonds) on the semiconductor surface [63, 64]. 

As outlined above, electron transfer through the passive film can also be cmcial for passivation and thus for the corrosion behaviour of a metal. Therefore, interest has grown in studies of the electronic properties of passive films. Many passive films are of a semiconductive nature [92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102 and 1031 and therefore can be investigated with teclmiques borrowed from semiconductor electrochemistry—most typically photoelectrochemistry and capacitance measurements of the Mott-Schottky type [104]. Generally it is found that many passive films cannot be described as ideal but rather as amorjDhous or highly defective semiconductors which often exlribit doping levels close to degeneracy [105]. 

Intermetallic compounds with gallium are used as semiconductors. Indium is used to coat other metals to protect against corrosion, especially in engine bearings it is also a constituent of low-metal alloys used in safety sprinklers. The toxicity of thallium compounds has limited the use of the metal, but it does find use as a constituent of high-endurance alloys for bearings. 

Molybdenum hexafluoride is classified as a corrosive and poison gas. It is stored and shipped in steel, stainless steel, or Monel cylinders approved by DOT. Electronic and semiconductor industries prefer the cylinders equipped with valves which have Compressed Gas Association (CGA) 330 outlets. 

Materials made of siHcon nitride, siHcon oxynitride, or sialon-bonded siHcon carbide have high thermal shock and corrosion resistance and may be used for pump parts, acid spray nozzles, and in aluminum reduction ceUs (156—159). A very porous siHcon carbide foam has been considered for surface combustion burner plates and filter media. It can also be used as a substrate carrying materials such as boron nitride as planar diffusion source for semiconductor doping appHcations. 

Corrosion. Copper and selected copper aHoys perform admirably in many hostile environments. Copper aHoys with the appropriate corrosion resistance characteristics are recommended for atmospheric exposure (architectural and builder s hardware), for use in fresh water supply (plumbing lines and fittings), in marine appHcations (desalination equipment and biofouling avoidance), for industrial and chemical plant equipment (heat exchangers and condensers), and for electrical/electronic appHcations (coimectors and semiconductor package lead-frames) (30) (see Packaging). 

Electroless nickel or nickel—lead alloys can improve the solderabiUty and braisabiUty of aluminum even when a continuous film is not present. Electroless nickel systems based on dimethylaminehorane reduciag agents are used to coat aluminum contacts and semiconductors (qv) ia the electronics iadustry. Newer uses iaclude corrosion-resistant electroless nickel topcoatings on electroless copper plating for radio frequency... 

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