Films, semiconductor oxide

Transparent semiconductor oxide films, such as tin oxide (Sn02) and zinc oxide (ZnO), produced by MOCVD are also being considered for photovoltaic applications. ]... 

Kashyout AB, Arico AS, Monforte G, Crea E, Antonucci V, Giordano N (1995) Electrochemical deposition of ZnFeS thin film semiconductors on tin oxide substrates. Sol Energy Mater Sol CeUs 37 43-53... 

To dissociate molecules in an adsorbed layer of oxide, a spillover (photospillover) phenomenon can be used with prior activation of the surface of zinc oxide by particles (clusters) of Pt, Pd, Ni, etc. In the course of adsorption of molecular gases (especially H2, O2) or more complex molecules these particles emit (generate) active particles on the surface of substrate [12], which are capable, as we have already noted, to affect considerably the impurity conductivity even at minor concentrations. Thus, the semiconductor oxide activated by cluster particles of transition metals plays a double role of both activator and analyzer (sensor). The latter conclusion is proved by a large number of papers discussed in detail in review [13]. The papers cited maintain that the particles formed during the process of activation are fairly active as to their influence on the electrical properties of sensors made of semiconductor oxides in the form of thin sintered films. 

If the above comparison of the properties of metal atoms with those of hydrogen deposited on the surface of a solid body (semiconductor) is correct, the effect of their adsorption on electric properties of semiconductor oxide films will be similar to features accompanying adsorption of hydrogen atoms. The atoms of hydrogen are very mobile and, in contrast to metal atoms, are capable of surface recombination resulting in formation of saturated molecules with strong covalent bond. 

Similar to the case of H-atoms the results obtained fully confirm the validity of expression v = 9Iz, where 9 is the degree of ionization depending on adsorbate, adsorbent, and the temperature. This means that ZnO films (it is also correct both for a CdO layer, and for other chemically stable semiconductor oxides) may be used as very sensitive miniature sensors to determine intensity of atom flow for detected noble metals Ag and Pd (see Table 3.2). If the sensitivity of the measuring equipment is brought up to one can measure atom flows equal to... 

All the aforesaid on the adsorption of acceptor atom and molecular particles lends support to the general conclusion of suitability of the designed sintered semiconductor oxide films (mainly ZnO) as highly sensitive semiconductor sensors meant to quantitatively detect extremely low concentrations of atom and molecular acceptor and donor particles in a concentration range of 10 -10 atoms per cubic centimetre in the volume adjacent to a semiconductor sensor. 

Electric effects detected in semiconductor oxide films during chemi-sorbtion of atom particles have been also thoroughly studied for chemi-sorbtion of various free radicals CH2, CH3, C2H5, C6H5OH2, OH, NH, NH2, etc. [41]. It was discovered that all of these particles have an acceptor nature in relation to the electrons of dope conductivity in oxide semiconductors their adsorption, as a rule, being reversible at elevated temperatures. It is clear that we deal with reversibility of electron state of the oxide film after it has been heated to more than 250-300°C in... 

This radicals do not escape from the surface (this is indicated by a semiconductor microdetector located near the adsorbent surface) undergoing chemisorption on the same semiconductor adsorbent Him. Thus, they caused a decrease in the electric conductivity of the adsorbent sensor, similarly to the case where free radicals arrived to the film surface from the outside (for example, from the gas phase). Note that in these cases, the role of semiconductor oxide films is twofold. First, they play a part of adsorbents, and photoprocesses occur on their surfaces. Second, they are used as sensors of the active particles produced on the same surface through photolysis of the adsorbed molecular layer. 

Further investigations of the above discussed effects show that, at fixed temperature of the oxide film (catalyst), the jump in the electric conductivity first increases in amplitude, as the portion of alcohol vapor admitted into the vessel increases. On further increase of the admitted portion of alcohol, the jump amplitude reduces (starting with the pressure of 3.6-10 2 Torr). At the pressure of 3.2-10 Torr, the jump in the electric conductivity of the zinc oxide film is less pronounced. Finally, at still higher pressures, it disappears (Fig.4.9). This effect is not unexpected. On our mind, it is associated with the fact that, as the concentration of alcohol vapor increases, the sum of the rate of interaction of the vapor with adsorbed hydrogen atoms and the rate of surface recombination of hydrogen atoms at the time instant of production becomes higher than the chemisorption rate of these atoms. The latter is responsible for the increase of the electric conductivity of the semiconductor oxide film via the reaction... 

The sensor detection of EEPs is methodically more complicated than the detection of atoms and radicals. With atoms and radicals being adsorbed on the surface of semiconductor oxide films, their electrical conductivity varies merely due to the adsorption in the charged form. If the case is that EEPs interact with an oxide surface, at least two mechanisms of sensor electrical conductivity changes can take place. One mechanism is associated with the effects of charged adsorption and the other is connected with the excitation energy transfer to the electron... 

In the active state, the dissolution of metals proceeds through the anodic transfer of metal ions across the compact electric double layer at the interface between the bare metal and the aqueous solution. In the passive state, the formation of a thin passive oxide film causes the interfadal structure to change from a simple metal/solution interface to a three-phase structure composed of the metal/fUm interface, a thin film layer, and the film/solution interface [Sato, 1976, 1990]. The rate of metal dissolution in the passive state, then, is controlled by the transfer rate of metal ions across the film/solution interface (the dissolution rate of a passive semiconductor oxide film) this rate is a function of the potential across the film/solution interface. Since the potential across the film/solution interface is constant in the stationary state of the passive oxide film (in the state of band edge level pinning), the rate of the film dissolution is independent of the electrode potential in the range of potential of the passive state. In the transpassive state, however, the potential across the film/solution interface becomes dependent on the electrode potential (in the state of Fermi level pinning), and the dissolution of the thin transpassive film depends on the electrode potential as described in Sec. 11.4.2. 

The rapid developments in the microelectronics industry over the last three decades have motivated extensive studies in thin-film semiconductor materials and their implementation in electronic and optoelectronic devices. Semiconductor devices are made by depositing thin single-crystal layers of semiconductor material on the surface of single-crystal substrates. For instance, a common method of manufacturing an MOS (metal-oxide semiconductor) transistor involves the steps of forming a silicon nitride film on a central portion of a P-type silicon substrate. When the film and substrate lattice parameters differ by more than a trivial amount (1 to 2%), the mismatch can be accommodated by elastic strain in the layer as it grows. This is the basis of strained layer heteroepitaxy. 

Copper electrodes have been used to determine amino acids and carbohydrates [10]. Metal oxide electrodes (including thin-film semiconductors) show some promise, but nothing of substance has yet been published with regard to LCEC. Pulsed amperometric detection (PAD) takes advantage of metal oxides formed in situ. This approach is discussed later. 

The rapid development of solid state physics and technology during the last fifteen years has resulted in intensive studies of the application of plasma to thin film preparation and crystal growth The subjects included the use of the well known sputtering technique, chemical vapour deposition ( CVD ) of the solid in the plasma, as well as the direct oxidation and nitridation of solid surfaces by the plasma. The latter process, called plasma anodization 10, has found application in the preparation of thin oxide films of metals and semiconductors. One interesting use of this technique is the fabrication of complementary MOS devices11. Thin films of oxides, nitrides and organic polymers can also be prepared by plasma CVD. 

Thns, Ch acts as a capacitor in series with the parallel combination of Csc and Css- hi many sitnations becanse of the presence of an oxide film on the surface, particularly for sihcon in non-HF electrolytes, an extra RC component is involved due to the charges and states in the oxide and at the semiconductor/oxide interface. The characteristics of these charges and states are discnssed in Chapter 3 on sihcon oxide. 

This chapter has not been organized historically to trace research that has culminated world-wide in the introduction of high-k dielectrics into commercial advanced semiconductor devices, but instead is organized to describe the experiments and theory that underpin the importance of J-T effects in nano-crystalline thin film TM oxides, most importantly in the intrinsic bonding defects that limit device performance and reliability [1]. 

Jones T A, Bott B, Hurst N W and Mann B 1983 Solid state gas sensors zinc oxide single crystals and metal phthalocyanine films Proc. Int. Meeting on Chemical Sensors (Analytical Chemistry Symposia Series 17, Fukuoda 1993) ed T Seiyama, K Fueki, J Shiokawa and S Suzuki (New York Elsevier) pp 90-4 Saeki H and Suzuki S 1992 Organic thin film semiconductor device Japanese Patent IPX 19881102 63-277732 US Patent 3 Q19 595 Lewis A 1967 The Palladium Hydrogen System (New York Academic)... 

Here, LHE(A) is the light harvesting efficiency for photons of wavelength X, 0mj is the quantum yield for electron injection from the excited sensitizer in the conduction band of the semiconductor oxide and r]coii is the electron collection efficiency. Having analyzed above the light harvesting efficiency of dye-loaded mesoscopic films we discuss now the other two parameters. 

Su P.-G., Wu R.-J., and Nieh F.-R, Detection of nitrogen dioxide using mixed tungsten oxide-based thick film semiconductor sensor, Talanta, 59, 667-672, 2003. 

J241 5 Thin-Film Semiconductors Deposited in Nanometric Scales Na2S203 is oxidized through the half[Pg.324]

In modem technology an increasing number of nonmetallic materials, such as semiconductors, oxides, ionic crystals, and polymers, is employed, which corrode or degrade via chemical rather than electrochemical mechanisms. Corrosion protection of these materials by inhibitors is currently only marginally studied and will be an important future challenge for inhibitor science. For the important case of oxides, similar concepts as employed for the stabilization of passive films in the inhibition of localized corrosion should be applicable. 

A thin film of oxide is left during the surface preparation of a highly polarizable semiconductor, which prevents an intimate contact between the metal and the conductor. The film is referred to as an interfadal layer . 

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