Growth and Characterization of Indium Monotelluride Crystals

Growth and Characterization of Indium Monotelluride Crystals

Semiconductors have become an inevitable part of human life. The beginning of the modern electronic technology goes back to the invention and elaboration of the semiconductor-based transistor by Bardeen, Brattain and Shockley in 1948. Thereafter, electronics industry has grown and become one of the worlds largest commercial establishments. The increasing demands for smaller electronic devices with improved performance at lower costs drive the conventional silicon-based technology to its limits. To satisfy the requirements from the industry and to extend the applications of semiconductor devices, new materials and fabrication techniques have to be used. The development, specification and quality control of these materials often require a very delicate crystal growth process and specific characterizations, which will be critical to a successful design of an electronic device. The knowledge of structural, electrical and mechanical properties of materials is essential for making use of them in various electronic devices. The operating abilities of a large part of modern technological hardware are based on active and/or passive crystalline core pieces. The fabrication of such crystals is normally connected with the well established growth methods such as Bridgman, Czochralski, Verneuil, zone melting, top seeded solution growth (TSSG), re-crystallization techniques, etc. Bulk crystal growth techniques are used to grow large crystals from which substrates are sliced. Substrate availability is a critical component in the success of a technology. Hence, even in this era of thin films and epitaxial layers, bulk crystal growth from melt still upholds its significance and plays an important role in the development of semiconductor-based technologies. Solar cell technology, as a sustainable source of energy, has shown a tremendous growth in recent years. The most widely used commercial solar cells are made from single crystalline silicon and have efficiencies up to 26.5%. However, such single crystalline solar cells are relatively expensive with the silicon itself making up to 20-40% of the final cost. In the search for low-cost alternatives to crystalline silicon, a great deal of work is being carried out in tailoring the applicability of compound semiconductor materials, which offer advantages over silicon. Indium monotelluride (InTe) is a III-VI layered semiconductor, which is particularly suitable for photovoltaic use, because of its suitable band gap (1.16 eV), optical and transport properties. In addition, its cleaved surfaces do not need any additional treatment for p??n junction formation and are chemically inert under ambient conditions. The crystal structure of InTe is tetragonal with lattice parameters, a = b = 8.454 ??, and c = 7.152 ??. The direct nature of transition supports the maximum efficiency of the InTe based opto-electronic devices. Indium monotelluride (InTe) crystals have been crystallized using directional freezing technique by employing a two zone horizontal furnace. The compound charge used for the growth was synthesised from its constituent elements (In and Te). The structural and chemical investigations of the grown samples were performed using powder x-ray diffraction (XRD) technique and energy dispersive analysis by x-rays (EDAX). The dielectric constant, loss factor, AC conductivity and optical band gap of the grown InTe crystals were estimated from the capacitance measurements in the temperature range, 35-140??C. The frequency dependence of these dielectric parameters has been studied to understand the mechanism behind conduction. The mechanical strength of the cleaved samples of indium monotelluride was investigated using Vickers microhardness tester in the load range, 5-50 g, and the results obtained are discussed. The present research work titled ??Growth and characterization of indium monotelluride crystals has been organized into four chapters. Chapter 1 gives a brief introduction about the concepts of nucleation with regard to the crystal growth of semiconducting materials. The effects of thermodynamical parameters on the growth of crystals are explained. The theories of crystal growth along with the factors affecting the crystallization phenomenon are described in chapter 2. The principle behind the different crystal growth processes is outlined. An account on the various crystal growth techniques highlighting their special features is also given. A review of the present national / international status on the growth and characterization of InTe is presented. The description of directional freezing method, experimental procedure and the various characterization techniques used for the study are presented in chapter 3. Chapter 4 covers the results and discussions of the research findings. It ends with a reference section, wherein the literature reviews used are listed as per the international standards and the order of its appearance in the text.

K. Munirathnam

Physics