Synthesis and characterisation of amorphous semiconductors

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Μπενέκου, Βασιλική
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Amorphous materials have attracted a lot of attention in the last decades. Their unique structure and properties as well as their application in devices are the two most significant reasons for all the research evolved around these materials. The “imperfections” of these materials are what makes them perfect. A lot of amorphous materials can be synthesized easily with low cost methods and they can be either produced in a bulk form or thin films and even fibers. Among these amorphous materials, chalcogenide glasses have been distinguished due to their unique structure and their ability to exhibit intrinsic photoinduced phenomena. The relatively high ratio of “free volume”, the possession of non-bonding orbitals along with their non-equilibrium nature are some of the reasons making these materials the perfect candidates for exhibiting unique photo-induced effects. These effects are used in a variety of applications such as the optical data storage, but more importantly they have intrigued the scientists because of the peculiar nature of some photo-induced phenomena. Photoamorphization is a very interesting and unique phenomenon which is not often observed. Though the discovery of this effect goes back to 1995, photoamorphization remains one of the least understood physical phenomena. The purpose of this thesis is to study several amorphous semiconductors with the use of Raman spectroscopy and other characterization techniques in order to further understand the structure of these unique materials and better explain some of the intriguing photoinduced phenomena exhibited by some of these systems. The use of Raman spectroscopy is very significant since most of the time it is used not only to record the structural changes of the materials but also to induce them in the first place (in-situ process). A unique three stage mechanism of an amorphous-crystal-amorphous phase transition is presented and studied in detail in order to explain the nature of these photo-induced structural changes. SEM images confirm the crystal growth upon photocrystallization. The kinetics of these phenomena are also studied in order to provide us with insight information concerning these phase changes. Another important aspect of this thesis is the effort to further explain photoamorphization of crystalline Orpiment. The nature of this effect still remains unclear and this study aims to help scientist better understand this phenomenon and prove its existence in the case of orpiment.
Amorphous semiconductors, Chalcogenide glasses, Photocrystallization, Photoamorphization, Raman spectroscopy, Orpiment