Schottky-type contacts

Some types of the polymers were investigated in detail. The photoconductivity of polyethylene with quantum efficiency 10 5-10 10 is caused by impurities, Schottky type contact injection, and hole transport [82,83], The crystallinity increase is accompanied by a photocurrent increase. There is no clear correlation between the chemical structure and the photocurrent. 

Metals, such as platinum, are usually introduced to improve the electron-hole separation efficiency. In order to analyze the energy structure of the metal-loaded particulate semiconductor, we solved the two-dimensional Poisson-Boltzmann equation.3) When the metal is deposited to the semiconductor by, for example, evaporation, a Schottky barrier is usually formed.45 For the Schottky type contact, the barrier height increases with an increase of the work function of the metal,4 which should decrease the photocatalytic activity. However, higher activity was actually observed for the metal with a higher work function.55 This results from the fact that ohmic contact with deposited metal particles is established in photocatalysts when the deposited semiconductor is treated by heat65 or metal is deposited by the photocatalytic reaction.75 Therefore, in the numerical computation we assumed ohmic contact at the energy level junction of the metal and semiconductor. 

Schottky-type contacts have also been reported. The occurrence of Schot-tky junctions is discussed in terms of the choice of semiconductor, the work... 

In a MESFET, a Schottky gate contact is used to modulate the source-drain current. As shown in Figure 14-6b, in an //-channel MESFET, two n+ source and drain regions are connected to an //-type channel. The width of the depletion layer, and hence that of the channel, is modulated by the voltage applied to the Schottky gate. In a normally off device (Fig. 14-9 a), the channel is totally depleted at zero gate bias, whereas it is only partially depleted in a normally on device (Fig. 14-9 b). 

Figure 23 Ohmic contact (a) and Schottky barrier contact (b) between a metal M and a p-type semiconductor SC. Energies , /, x> and Eg are defined in text. Ef, Fermi level VB valence band, or hole conducting levels CB, conduction band, or electron conducting levels. Dots indicate the acceptors crosses indicate the holes in the SC outside the depletion layer.

Schottky-type cell. A thin organic film is sandwiched between two different metals, which form a blocking and an ohmic contact. 

As mentioned earlier, photochemical diodes489 can be either of the Schottky type, involving a metal and a semiconductor, or a p n junction type, involving two semi conductors (which can be the same, i.e., a homojunction or different, a heterojunc tion). Only the latter type is considered in this Section involving two irradiated semi conductor/ electrolyte interfaces. Thus n Ti02 and p-GaP crystal wafers were bonded together (through the rear Ohmic contacts) with conductive Ag epoxy cement.489 The resultant heterotype p n photochemical diode was suspended in an acidic aqueous... 

J. F. DEWALD (Bell Telephone Laboratories) I do not believe that the effect of semiconductivity on catalysis is completely contained in either the Schottky or the Mott-Schottky approximations. Consider a supported metal catalyst. If one has an exhaustion layer on an n-type support then the total charge in the exhaustion layer would be very small. The potential, acting over so large a distance, would have very little effect on catalysis. If, however, you can cause an electron enrichment layer in the vicinity of the metal-n-type contact, you might expect very much larger catalytic effects, for there would be much larger electric fields near the point of contact. 

The type (1) interface is an ideal Schottky barrier contact in which the barrier height varies directly with the metal work function in accordance with Equation [3.18], The type (2) interface approximates to a Bardeen barrier, provided that the surface states are assumed to be spaced inside the semiconductor so as to allow a potential drop across this region. In the clean contacts of this type, one would expect the barrier height to show a weak dependence on 0 ,.The type (3) interface represents a case of strong chemical bonding between the metal and the semiconductor and, hence, we would expect the barrier height to depend on some quantity related to chemical or metallurgical reactions at the interface. The type (4) contact is the one most frequently encountered in actual metal-semiconductor devices. 

The many variations of the diode structure of Fig. 8 include the so-called Schottky barrier diode, a simple metal-semiconductor structure, usually gold on gallium arsenide. Here the metal is biased negative with respect to an n-type or intrinsic semiconductor with a heavily doped n-type contact layer. Gallium arsenide has a 10-fold larger... 

To consider the photolysis of water based on the inorganic equivalent of the Z-scheme in nature, semiconductor tandem-type structures, such as shown in Fig. 17, can be analyzed. It should be noted that the structure shown in Fig. 17 represents a solid state analogon of two half-cells for the photoelectrolysis of water in a joint scheme. Therefore, compared to solid state devices with two pn junctions, the band bending of the structure shown develops at the respective electrolyte contact or by forming Schottky-type junctions with the electrocatalysts at the surfaces which then... 

Films of phthalocyanine incorporated poly-N-vinyl carbazole on nesa glass in contact with aqueous electrolytes are used as sensitive dioxygen senors [229], Their photovoltaic property depends on the presence of oxygen or otherwise. Their incorporation onto polyimides is found to improve the cell s stability and performance. The use of other materials such as active carbon, alumina, silica, etc. as matrix materials for the incorporation of phthalocyanine has also been reported [70]. A non-Schottky-type rectifying device based on NiPc/Cu(PcFg), developed by vapour deposition, was shown to exhibit an I-V profile similar to a conventional p-n junction diode, with unconventional behaviour of large emission coefficient ( /) values [230]. 

Upon contacting a semiconductor with metallic electrodes the Fermi levels on both sides of either contact have to equilibrate. This is accomplished by charge exchange across the interface. In doped inorganic semiconductors the charges are delivered via impurity ionization. It gives rise to the formation of a Schottky-type depletion layer whose thickness is being the density of donor/acceptor states and V... 

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