Carrier Transport Processes in Amorphous Solids

3 Significance of Carrier Transport Data in Various Applications 42 

During the past decades, increasing use was made of amorphous semiconductor films, which not only offer the advantage of reduced cost, but are readily produced as large-area elements of the type required in applications. 

The successful use of noncrystalline semiconductors in various applications depends on the development of our understanding of electronic conduction in these materials to a standard comparable to that which presently exists in the case of their crystalline counterparts. 

For many years, during and after the development of the modem band theory of electronic conduction in crystalline solids, it was not considered that amorphous materials could behave as semiconductors. The occurrence of bands of allowed electronic energy states, separated by forbidden ranges of energy, to become firmly identified with the interaction of an electronic waveform with a periodic lattice. Thus, it proved difficult for physicists to contemplate the existence of similar features in materials lacking such long-range order. 

Trap Level Spectroscopy in Amorphous Semiconductors. DOI 10.1016/B978-0-12-384715-7.00003-6 

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Before presenting some additional experimental observations, we pause to discuss, qualitatively, how the foregoing trends and dependences may be understood. (A quantitative theory of charge transport in amorphous molecular solids will be discussed later.) In any charge transport process, whether the carriers are electronic or ionic, and whether the mediiun is crystalline, amorphous, or fluid, each individual carrier undergoes a random walk in which there is a preference (large or small, de-... 

One of the most interesting aspects of the physics and chemistry of organic solids is their ability to conduct optical excitation energy within the crystal or even in amorphous material and to transfer it. Energy which is absorbed at one place in the solid can be transported to another place where it can be used to induce various processes which require energy. Such processes include sensitised luminescence, the generation of free charge carriers and photochemical reactions. 

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