The earliest experimental data on an oxygen-free glass have been published by Schulz-Sellack in 1870 [1]. Later on, in 1902, Wood [2], as well as Meier in 1910 [3], carried out the first researches on the optical properties of vitreous selenium. The interest in the glasses that exhibit transparency in the infrared region of the optical spectrum rose at the beginning of the twentieth century. Firstly were investigated the heavy metal oxides and the transparency limit was extended from (the case of the classical oxide glasses) up to wavelength. In order to extend this limit above the scientists tried the chemical compositions based on the elements of the sixth group of the Periodic Table, the chalcogens: sulphur, selenium and tellurium. The systematic research in the field of glasses based on chalcogens, called chalcogenide glasses, started at the middle of our century. In 1950 Frerichs [4] investigated the glass and published the paper: “New optical glasses transparent in infrared up to 12 . Several years later he started the study of the selenium glass and prepared several binary glasses with sulphur [5]. Glaze and co-workers [6] developed in 1957 the first method for the preparation of the glass at the industrial scale, while Winter-Klein [7] published reports on numerous chalcogenides prepared in the vitreous state.

The earliest experimental data on an oxygen-free glass have been published by Schulz-Sellack in 1870 [1]. Later on, in 1902, Wood [2], as well as Meier in 1910 [3], carried out the first researches on the optical properties of vitreous selenium. The interest in the glasses that exhibit transparency in the infrared region of the optical spectrum rose at the beginning of the twentieth century. Firstly were investigated the heavy metal oxides and the transparency limit was extended from (the case of the classical oxide glasses) up to wavelength. In order to extend this limit above the scientists tried the chemical compositions based on the elements of the sixth group of the Periodic Table, the chalcogens: sulphur, selenium and tellurium. The systematic research in the field of glasses based on chalcogens, called chalcogenide glasses, started at the middle of our century. In 1950 Frerichs [4] investigated the glass and published the paper: “New optical glasses transparent in infrared up to 12 . Several years later he started the study of the selenium glass and prepared several binary glasses with sulphur [5]. Glaze and co-workers [6] developed in 1957 the first method for the preparation of the glass at the industrial scale, while Winter-Klein [7] published reports on numerous chalcogenides prepared in the vitreous state.

This book provides introductory, comprehensive, and concise descriptions of amorphous chalcogenide semiconductors and related materials. It includes comparative portraits of the chalcogenide and related materials including amorphous hydrogenated Si, oxide and halide glasses, and organic polymers. It also describes effects of non-equilibrium disorder, in comparison with those in crystalline semiconductors.

The medium range order in disordered chalcogenides has been explained by the existence of reminiscent crystal-like configurations with distorted arrangement of the atoms. Using the paracrystalline theory, two parameters have been defined for the characterization of the MRO in glass: paracrystallite thickness and paracrystallite distortion.

The Workshop on Physics and Application of Non-crystalline Semiconductors in Optoelectronics was held from 15 to 17 October 1996 in Chisinau. republic of Moldova and was devoted to the problems of non-crystalline semiconducting materials. The reports covered two mjlin topics: theoretical basis of physics of non -crystalline materials and experimental results. In the framework of these major topics there were treated many subjects. concerning the physics of non-crystalline semiconductors and their specific application: -optical properties of non-crystalline semiconductors; -doping of glassy semiconductors and photoinduced effects in chalcogenide glasses and their application for practical purposes; -methods for investigation of the structure in non-crystalline semiconductors -new glassy materials for IR trasmittance and optoelectronics. Reports and communications were presented on various aspects of the theory. new physical principles. studies of the atomic structure. search and development of optoelectronics devices. Special attention was paid to the actual subject of photoinduced transformations and its applications. Experimental investigations covered a rather wide spectrum of materials and physical phenomena. As a novel item it is worth to mention the study of nonlinear optical effects in amorphous semiconducting films. The third order optical non linearities. fast photoinduced optical absorption and refraction. acusto-optic effects recently discovered in non-crystalline semiconductors could potentially be utilised for optical signal processing. The important problems of photoinduced structural transformations and related phenomena. which are very attractive and actual both from the scientific and practical points of view. received much attention in discussions at the conference.

This second edition deals in an elementary way with electrons in non-crystalline systems. It reflects advances in the theory of interactions in non-crystalline systems, provides a more detailed discussion of the "minimum metallic conductivity", and addresses the relevance of disorder in the new high-temperature semiconductors.