The concepts of translational symmetry and long-range order in atomic arrangement relating to single crystals are the pillars of modern solid state physics. However, single crystals are a very special case of the solid state. Long-range order is absent in most materials. Therefore, the future of solid state physics lies in developing a theory that would describe the different states of matter while including the theory of single crystals as a special case. Besides being of academic interest, materials without long-range order are important from the application point of view. Devices based on disordered semiconductors have very wide applications: electrophotographic printers and copiers, liquid crystal displays and monitors, optical discs, cheap solar cells and others. However, the peculiarities of disordered semiconductors call for new approaches to the device design compared with traditional single-crystal materials. For example, the absence of long-range order in structural network allows for applying new methods of properties control without any doping. Moreover, with a correct approach the so-called inherent disadvantages of disordered semiconductors can be used to the advantage of the devices. For example, low charge carrier mobility allows for combining the high resistivity of materials with photosensitivity in the visible part of the spectrum and for creating electrophotography equipment.
The goal of this textbook is to link characteristic features of atomic and electronic structures of disordered semiconductors to the device design process. The textbook begins with a description of general concepts of disordered semiconductors, their atomic structures, the structure of energy bands, their defects, as well as their electrical, optical and photovoltaic properties. Since weak sensitivity to impurities is a distinguishing feature of disordered semiconductors, methods of property control and thin-film preparation methods are the areas of focus. Finally, applications of disordered semiconductors in various devices are considered.
