Schottky-type devices

In principle there are two types of solid state devices (i) pn-photocells and (ii) Schottky type cells. The first one consists simply of a pn-junction whereas the other of a semi-conductor-metal junction. The energy schemes of these cells are given in Fig. 1 a and b. The current-potential dependence of both types of cells is given by (see e.g. ) ... 

Recent experiments determining the so-called chemicurrent [111] have provided some information on the importance of electron-hole pair excitation in adsorption processes. Using thin films deposited on n-type Si(l 1 1) as a Schottky diode device, the nonadiabatically generated electron-hole pairs upon both atomic and molecular chemisorption create the chemicurrent which can be measured [111, 112]. It has been estimated that for example in the NO adsorption on Ag one quarter of the adsorption energy is dissipated to electron-hole pairs. Adsorption-induced electron-hole pair creation has also been found for other metal substrates, such as Au, Pt, Pd, Cu, Ni and Fe, and even for semiconductors such as GaAs and Ge [112, 113]. 

It is evident from Eq. (94) that the maximum photovoltage depends critically on the exchange current Jo- In the case of pn-junctions, jo is determined by the injection and recombination (minority carrier device). Whereas in Schottky-type of cells jo can be derived from the thermionic emission model (majority carrier device). The analysis of solid state systems has shown that jo is always smaller for minority carrier devices [20,21]. Using semiconductor-liquid junctions, both types of cells can be realized. If in both processes, oxidation and reduction, minority carrier devices are involved, then jo is given by Eq. (37a), similarly as... 

Using SiNWs fabricated by various methods, resistive gas sensors (Gao et al. 2010 Field et al. 2011), FET (McAlpine et al. 2007 Paska et al. 2011), Schottky type gas sensors (Skucha et al. 2010), and field-ionized gas sensors (Sadeghian and Islam 2011) have been designed. Examples of such devices... 

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]. 

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). 

The decrease in free carriers (holes) after hydrogenation of p-type Si is also evidenced by the decrease in IR absorption at the longer wavelengths, where free-carrier absorption dominates, and by a decrease in the device capacitance of Schottky-barrier diodes, due to the increase in the depletion width (at a given reverse bias) as the effective acceptor concentration decreases. 

The simplest electronic devices, such as diodes, light-emitting diodes, lasers, and photocells, have a single p-n junction. If we place, say, a p-type doped Si block in contact with n-typed doped Si block, electrons will normally flow from the n to the p regions but not vice versa. Thus, the p-n diode so created can be fitted with ohmic contacts to function as a rectifier of alternating current. Schottky junctions can act in this way to some degree even without deliberate creation of a p-n junction. 

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