Oxide semiconductor

General reviews of the use of oxide semiconductors for the photoelectrolysis of water are contained in Refs. 62 and 65 (see Table 1). Eleven binary and ternary oxides were examined in Ref. 62. Linear correlations were presented between the flat band potential, Vtb of these oxides and their band gap energy (Eg) and between Vm and the heat of formation of the oxide per metal atom per metal-oxygen bond. Aligning all the oxide energy levels on a common scale, these authors noted62 that the position of the conduction band varies much more than those of valence bands - a trend expected from the cationic (d-band) character of the conduction band in the oxide while the valence band is mainly of 0(2p) character. The latter should be relatively independent of the oxide parentage in terms of the metal. 

The possibility of introducing new d-bands for Type b oxides (with filled d-bands) by introducing dopants into the host lattice was also discussed in Ref. 65 with examples. Other authors have advocated this approach as well (Ref. 26, for exam pie). The review in Ref. 32 contains further examples of this approach for effectively shrinking the original Eg and sensitizing the oxide to visible portions of the solar spectrum. We shall return to this aspect for the specific case of TiCte later in this Chapter. 

We now turn to discussions of individual oxide semiconductor materials for the photoelectrolysis of water, starting with the mother of all oxides, namely, TiC 2. 

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Dadap J I, Hu X F, Anderson M H, Downer M C, Lowell J Kand Aktsiperov O A 1996 Optical second-harmonic electroreflectance spectroscopy of a Si(OOOI) metal-oxide-semiconductor structure Phys. Rev. B 53 R7607-9... 

Figure Bl.22.4. Differential IR absorption spectra from a metal-oxide silicon field-effect transistor (MOSFET) as a fiinction of gate voltage (or inversion layer density, n, which is the parameter reported in the figure). Clear peaks are seen in these spectra for the 0-1, 0-2 and 0-3 inter-electric-field subband transitions that develop for charge carriers when confined to a narrow (<100 A) region near the oxide-semiconductor interface. The inset shows a schematic representation of the attenuated total reflection (ATR) arrangement used in these experiments. These data provide an example of the use of ATR IR spectroscopy for the probing of electronic states in semiconductor surfaces [44]-...

Figure C2.16.9. Schematic cross-section and biasing of a metai-oxide-semiconductor transistor. A unifonn conducting channei is induced between source (S) and drain (D) for > V. Voitage is appiied between the gate (G) and the source. Part (A) shows the channei for - V the transistor acts as a triode. The source-...

Metal oxide semiconductor field-effect transistor pOSFEQ... 

BSG = borosilicate glass PSG = phosphosilicate glass MOS = metal oxide semiconductor. 

Main memories almost exclusively consist of semiconductors on a siUcon basis in complementary metal oxide semiconductor technology (CMOS). The most important types are the pure read only memory (ROM) and the write/read memory (RAM = random access memory), which is available as S-RAM (static RAM) or as D-RAM (dynamic RAM). 

Gate oxide dielectrics are a cmcial element in the down-scaling of n- and -channel metal-oxide semiconductor field-effect transistors (MOSEETs) in CMOS technology. Ultrathin dielectric films are required, and the 12.0-nm thick layers are expected to shrink to 6.0 nm by the year 2000 (2). Gate dielectrics have been made by growing thermal oxides, whereas development has turned to the use of oxide/nitride/oxide (ONO) sandwich stmctures, or to oxynitrides, SiO N. Oxynitrides are formed by growing thermal oxides in the presence of a nitrogen source such as ammonia or nitrous oxide, N2O. Oxidation and nitridation are also performed in rapid thermal processors (RTP), which reduce the temperature exposure of a substrate. 

Plasma etching is widely used in semiconductor device manufacturing to etch patterns in thin layers of polycrystaUine siUcon often used for metal oxide semiconductor (MOS) device gates and interconnects (see Plasma TECHNOLOGY). 

Semiconducting Ceramics. Most oxide semiconductors are either doped to create extrinsic defects or annealed under conditions in which they become non stoichiometric. Although the resulting defects have been carefully studied in many oxides, the precise nature of the conduction is not well understood. Mobihty values associated with the various charge transport mechanisms are often low and difficult to measure. In consequence, reported conductivities are often at variance because the effects of variable impurities and past thermal history may overwhelm the dopant effects. 

Fig. 1. Technological trends A, components per chip B, minimum feature length , metal oxide semiconductor (MOS) memory A, bipolar memory I MOS logic n, bipolar logic. The designations SSI, MSI, LSI, and VLSI stand for small-, medium-, large-, and very large-scale iategration, respectively.

For example, chloride and duoride ions, even in trace amounts (ppm), could cause the dissolution of aluminum metallization of complimentary metal oxide semiconductor (CMOS) devices. CMOS is likely to be the trend of VLSI technology and sodium chloride is a common contaminant. The protection of these devices from the effects of these mobile ions is an absolute requirement. The use of an ultrahigh purity encapsulant to encapsulate the passivated IC is the answer to some mobile ion contaminant problems. 

FfCURE 13.54 Semiconductor gas sensors (o) tubular, (b) thick film, (e) bulk-type one-electrode sensor where a thin Pt wire spiral is embedded Inside a sintered oxide semiconductor button. ... 

A novel development of the use of ion-selective electrodes is the incorporation of a very thin ion-selective membrane (C) into a modified metal oxide semiconductor field effect transistor (A) which is encased in a non-conducting shield (B) (Fig. 15.4). When the membrane is placed in contact with a test solution containing an appropriate ion, a potential is developed, and this potential affects the current flowing through the transistor between terminals Tt and T2. 

M. McD. Baker and G. I. Jenkins Chemisorption and Catalysis on Oxide Semiconductors... 

Several demonstrations of this concept have recently been published The first one is based on the pH dependence of redox transitions in oxide semiconductors that are connected with conductivity changes. If the bridging polymer layer in Fig. 6 is WO3 sputtered onto the electrode array or electrochemically deposited Ni(OH)j the transistor amplification is a function of the pH of the... 

Nanocrystals are receiving significant attention for nano-electronics application for the development of future nonvolatile, high density and low power memory devices [1-3]. In nanocrystal complementary metal oxide semiconductor (CMOS) memories, an isolated semiconductor island of nanometer size is coupled to the channel of a MOS field effect transistor (MOSFET) so that the charge trapped in the island modulates the threshold voltage of the transistor (Fig. 1). 

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