Wide band-gap electronics materials

As mentioned earlier, CL is a powerful tool for the characterization of optical properties of wide band-gap materials, such as diamond, for which optical excitation sources are not readily available. In addition, electron-beam excitation of solids may produce much greater carrier generation rates than typical optical excitation. In such cases, CL microscopy and spectroscopy are valuable methods in identifying various impurities, defects, and their complexes, and in providing a powerful means for the analysis of their distribution, with spatial resolution on the order of 1 pm and less. ... 

Let us now briefly consider the various steps in a typical TSL or TSC experiment in wide-band gap material. We choose electromagnetic radiation as a means of excitation. The interaction of this radiation with the solids leads to a number of electronic phenomena, many of which are not clearly understood. They include the production of new defects as well as filling of trap levels with electron and holes ... 

On the other hand, oxide semiconductor materials such as ZnO and 2 have good stabilities under irradiation in solution. However, such stable oxide semiconductors cannot absorb visible light because of their wide band-gap character. Sensitization of wide-band-gap oxide semiconductor materials by photosensitizers, such as organic dyes which can absorb visible light, has been extensively studied in relation to the development of photography technology since the middle of the nineteenth century. In the sensitization process, dyes adsorbed onto the semiconductor surface absorb visible light and excited electrons of dyes are injected into the conduction band of the semiconductor. Dye-sensitized oxide semiconductor photoelectrodes have been used for PECs. 

The wide band gap semiconductor ZnO has attracted much attention in recent years. This is stimulated by the development of transparent electronics, the growing need of emitters and detectors working in the ultraviolet range of the electromagnetic spectrum, and the progress in the realization of ferromagnetic semiconductors with Curie temperatures close to or above room temperature. ZnO is nowadays applied as transparent front contacts of solar cells competing with the commonly used material indium tin oxide (ITO). The low cost of ZnO as well as the radiation hardness make... 

---