Zinc oxide electrical properties

Heterogeneous Photocatalysis. Heterogeneous photocatalysis is a technology based on the irradiation of a semiconductor (SC) photocatalyst, for example, titanium dioxide [13463-67-7] Ti02, zinc oxide [1314-13-2] ZnO, or cadmium sulfide [1306-23-6] CdS. Semiconductor materials have electrical conductivity properties between those of metals and insulators, and have narrow energy gaps (band gap) between the filled valence band and the conduction band (see Electronic materials Semiconductors). 

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. 

Zinc oxide is certainly not unique in exhibiting a strong correlation between adsorption and its electrical and optical properties. 

In this section, we have presented evidence to indicate that adsorbed oxygen on the surface may be a controlling factor in the electrical properties of zinc oxide. In the following section, the electron transfer theory of adsorption will be discussed. The properties then will be examined in more detail, agreement of the results with those predicted by the adsorption theory will be emphasized, and the contribution of those that have been studied to a more complete understanding of adsorption phenomena will be discussed. 

It is proposed that on zinc oxide the adsorption of oxygen has an important effect on the electrical properties. This has been supported by direct evidence relating the electrical effects to oxygen pressure over a wide range of temperatures (20°C to 800°C), and in addition has been supported by abundant indirect evidence. 

Zinc oxide (ZnO) can exhibit a wide range of electrical properties depending on minor constituents and sintering conditions. It is also remarkable for the ease with which high-density ceramics can be achieved over a wide range of sintering temperatures and for its excellent resistance to thermal shock. 

In this book the chemical, structural, optical, electrical, and interface properties of zinc oxide are summarized with special emphasis on the use of ZnO as transparent conductive electrode in thin film solar cells. This application has a number of requirements, which can be fulfilled by ZnO ... 

It should not be supposed that crystal defects enter into the picture only as nuisances which the chemist seeks to avoid or eliminate. Actually, certain optical and electrical properties of oxides, sulfides, and halides have been found to depend strongly on the nature and extent of crystal defects. Indeed, semiconductivity, fluorescence (absorption of radiation and emission of less energetic radiation), and phosphorescence (delayed fluorescence) of some salts may be spectacularly increased, not only by a small stoichiometric excess of one of the constituents, but also by addition of very tiny quantities of a foreign ion. Perhaps the best known example is the case of zinc sulfide which, when precipitated from aqueous solution and dried at low temperatures, shows negligible fluorescence upon exposure to ultraviolet light. When the sulfide is heated to... 

Kim, K. H., Park, K. C. and Ma, D. Y. (1997). Structural, electrical and optical properties of aluminum doped zinc oxide films prepared by radio frequency magnetron sputtering. J. Appl. Phys. 81(12), 7764-7772. 

Recently, there has been a significant increase of research in the field of zinc oxide. This is mainly driven by its extraordinary electrical and optical properties that enable a variety of applications ranging from piezoelectrical... 

Zinc is also a primary metal in the penny coin, which used to be made of copper. In addition, zinc can be mixed with copper to form brass, which is a very useful alloy because of its durability and hardness. Another useful compound is zinc oxide. Made by burning zinc vapor in air, zinc oxide is used to make white paints. Used as an ointment, zinc oxide makes a good sunscreen because it blocks the Suns harmful ultraviolet rays that damage the skin. Zinc oxide also has another important property it is photoconductive, which means that it conducts electricity better when exposed to light. For example, a photocopier contains a photoconductive plate that is sometimes made with zinc oxide. When this plate is electrically... 

Critical properties of TCO coatings are electrical resistance and transparency [3], but for solar cell applications very often texture and large haze factors, i.e., ratio of diffuse to total transmission, have similar importance. Large haze factors have been shown to influence positively the efficiency of silicon solar cells, because the reflection at the TCO-silicon interface is reduced and the scattering increases the pathway of light inside the active material. The preparation and characteristics of several TCO materials have been reviewed by Chopra et al. [92] and Dawar and Joshi [93]. The optical and electrical properties of ITO and aluminum doped zinc oxide have been studied in detail by Granqvist and coworkers [94, 95], but these films were prepared by sputtering and not by CVD. Very recently they also published an overview of transparent conductive electrodes for electrochromic devices [7]. 

Transparent conductive coatings combine high optical transmission with good electrical conductivity. The existence of both properties in the same material is, from the physics point of view, not trivial and is only possible with certain semi-conductors like indium oxide, tin oxide, cadmium oxide, and with thin gold and silver films, e.g. [157]. Particularly antimony or fluorine doped tin oxide (ATO, FTO), tin doped indium oxide (ITO), and aluminium, indium, or boron doped zinc oxide (AZO, IZO, BZO) are of technical importance [157a]. 

---