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GROWTH AND CHARACTERIZATION OF InBi1-xSbx, InBi1-xTex AND γ-In2Se3 CRYSTALS

AJAYAKUMAR , C J (2017) GROWTH AND CHARACTERIZATION OF InBi1-xSbx, InBi1-xTex AND γ-In2Se3 CRYSTALS. PhD thesis, Christ University.

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Abstract

Theory and innovating practices of crystal growth heralded cutting edge breakthroughs in the production of proficient crystals towards the advancement of science and technology. Detailed knowledge on the intrinsic physical properties requires good quality, defect free single phase crystalline samples and hence, recent years have witnessed a surge of activities in their evolution and development. Unique characteristics and band structure provide great flexibility for structural design and band gap engineering of indium bismuthide (InBi) compounds. Substitution of antimony and tellurium elements results in the transition of InBi to a semiconducting state with narrow energy gap, making it suitable for optoelectronic devices. Need of eco-friendly sustainable processes concerning the elimination of hazardous materials bring γ-In2Se3 in the forefront of photovoltaic industry, due to its wide band gap as well as ntype conductivity. Thus, realizing the immense potential attributes of InBi1-xSbx, InBi1-xTex (x = 0-0.2) and γ-In2Se3 crystals, the present research was focussed on pioneering their growth and characterization. Complexities were associated with conventional melt growth such as Bridgman-Stockbarger and Czochralski methods for preparation of bulk crystals with regard to irregular heat flow, thermal stress, impurity pick-up, etc. in addition to cost intensive arrangement. Hence, horizontal directional solidification (HDS), being the versatile inexpensive melt growth technique, was employed for obtaining InBi1-xSbx, and InBi1-xTex (x = 0-0.2) crystals. On the other hand, closed tube sublimation (CTS) was found to be most effective for deposition of γ-In2Se3 crystals. The current research problem was aspired at producing stoichiometric crystals with less imperfection. Therefore, by utilizing CTS, good quality samples with well-defined planes and superior mechanical strength were deposited. Crystals obtained using this method are free from external impurities and possessed very low dislocation density. Platelet and spherulitic morphologies of γ-In2Se3 crystals have been grown by the vapor deposition for the first time, under different growth environments. Photoluminescence emission energy and optical band gap data were found to be superior for device fabrication. Photocurrent was increased by three orders of magnitude compared to dark current. Good photosensitivity, small leakage current, wide band gap and remarkable hardness make them suitable for photovoltaic industry. Morphology, structure and quality of the as-grown crystals were studied, employing various scientific procedures such as X-ray diffraction (XRD), energy dispersive analysis by X-rays (EDAX), scanning electron microscopy (SEM), atomic force microscopy (AFM) and transmission electron microscopy (TEM). Transport parameters have been evaluated with the aid of Hall effect measurement system and four probe set up. Differential scanning calorimetry (DSC) and Raman spectroscopy were used for assessing the melting point and phase purity. Vickers indentation testing was utilized for the evaluation of microhardness and deformation characteristics. Fourier transform infrared (FTIR) and photoluminescence spectrometers have been employed for band gap computation. Conduction mechanisms and surface quality were examined with LCR impedance meter as well as photoconductivity device. Structural, morphological, optical, electrical and mechanical properties of indium bismuthide were investigated by doping with antimony as well as tellurium, making it ideal for infrared applications. Substitution of foreign elements changes the semimetallic attribute of InBi to semiconducting nature. Influence of 60-Co gamma ray irradiation on the grown samples was also analyzed to explore their suitability in radiation environment. Thus, the adopted HDS and CTS methods involving optimization of growth conditions are boon to the deliverance of good quality, structurally perfect crystals with precise control of composition and properties for optoelectronic applications. The executed scientific research work has been customized to meet the objectives and organized in the thesis as follows. Chapter 1 gives an overview of literature showing the emerging trends of InBi, In2Se3 and related compounds. Various aspects on the theories of nucleation, growth mechanism and techniques are narrated. This chapter also explains the objectives of present research problem. Chapter 2 describes the experimental methodology for growth of crystals by horizontal directional freezing (HDS) as well as closed tube sublimation (CTS) processes. A brief account of selected characterization tools is also included in the chapter. Detailed description on the morphology, growth mechanism, compositional and structural analysis of InBi1-xSbx crystals is given in chapter 3. By employing XRD, SEM, EDAX, AFM, Raman and FTIR spectroscopy, the various physical parameters controlling phase and structure of grown samples were elucidated. The growth and characterization of InBi1-xTex (x = 0-0.2) crystals by horizontal directional freezing technique is highlighted in chapter 4. Chapter 5 deals with the effect of Co-60 gamma ray exposure on crystallinity, electrical, and optical properties of doped crystals. Chapter 6 reports the growth of gamma indium selenide crystals by closed tube sublimation method. A detailed analysis of the structure, morphology, composition, photoconductivity and photoluminescence of vapor deposited γ-In2Se3 platelet samples is also presented. Results and conclusions of the overall research findings are summarized in chapter 7.

Item Type:Thesis (PhD)
Subjects:Thesis
Thesis > Ph.D > Physics
Thesis > Ph.D
ID Code:7776
Deposited By:Shaiju M C
Deposited On:10 May 2019 12:44
Last Modified:11 May 2019 12:43

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