Semiconductors defects

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]. 

The unique electronic properties of semiconductor devices arise at the regions where p-typc and ra-typc materials ate in close proximity, as in p-n junctions. Typical impurity levels ate about 0.0001 at %, and their inclusion and distribution need to be very strictly controlled during preparation. Without these deliberately introduced point defects, semiconductor devices of the type now commonly available would not be possible. 

At all temperatures above 0°K Schottky, Frenkel, and antisite point defects are present in thermodynamic equilibrium, and it will not be possible to remove them by annealing or other thermal treatments. Unfortunately, it is not possible to predict, from knowledge of crystal structure alone, which defect type will be present in any crystal. However, it is possible to say that rather close-packed compounds, such as those with the NaCl structure, tend to contain Schottky defects. The important exceptions are the silver halides. More open structures, on the other hand, will be more receptive to the presence of Frenkel defects. Semiconductor crystals are more amenable to antisite defects. 

I For the case of copper, a mixture of cuprous and cupric oxides is present on the copper surface which acts as a defect semiconductor. Therefore, electrons can readily be transported from copper to its oxide surface allowing oxidation to continue at the metal oxide/adhesive interface ls. This continued oxidation reaction which involves the base metal can interfere with adhesion between the oxide and the adhesive. Hence, the underlying metal atoms can effect the adhesion forces in some cases 171... 

The j9-type or defect semiconductor has the formula Nii 0. Metals that form such j9-type oxides are those that exist in several oxidation states. The oxides contain the lower oxidation state form (e.g., Ni ", Co ", Cu" ), which can then enter the higher oxidation state (Ni ", Co ", Cu ". The n-type oxides, in contrast, are those that exist in only one oxidation state or in which the highest state is present (e. g., Zn0,Ti02,V205, M0O3, Fe203). 

Gallium selenides exhibit semiconductor properties [6, 7]. 603803 belongs to the defect semiconductor group A bJ [8]. 

D. Macdonald [1999] Cation/interstitial/ anion conductors Constrained by Esaki tunneling Cation injection from metal or anion vacancy generation at the m/bl interface Yes Yes Highly doped (degenerate), defect semiconductor... 

It should be noted, though that defective semiconductors - for instance oxide layers on metals - typically do not show an ideal capacitive behavior which often leads to a strong frequency-dependence of the capacitance. There are many possible reasons for non-ideal behavior such as ionic participation , a frequency-dependent dielectric constant, contributions from the Helmoltz-layer or from surface states, non-ideal structure or nonideal donor distribution, as well as inhomogeneous depth distribution in the composition or structure of the oxide layer. Independent of the origin of the non-ideal behavior, the frequency dispersion can partially be corrected by replacing the capacitance in impedance fits by a so-called constant phase element (CPE), which takes into consideration the non-ideal nature of a capacitance. While the introduction of CPE may eliminate the... 

Signals due to technical imperfections or deterioration of the seismic Passive Seismometers (corrosiOTi, leakage currents, defective semiconductors, etc.)... 

In addition to atomic point defects, semiconductor materials can also have electronic point defects. These defects provide mobile charge carriers that move about the crystal lattice. They provide the basis for many useful applications. In fact, the entire microelectronics industry is based on being able to control electronic defects in these materials. 

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