Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Molecular Beam Epitaxial Growth of Znse on (211)b Gaas(Izmir Institute of Technology, 2017) Yavaş, Begüm; Özçelik, Serdar; Ateş, Serkan; Ateş, Serkan; Özçelik, Serdar; 04.01. Department of Chemistry; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of TechnologyThe Mercury Cadmium Telluride (Hg1-xCdxTe) play important role for infrared (IR) focal plane array application. It is grown on variety alternative substrates which are Si, Ge, GaAs or GaSb. When GaAs is compared with the others alternative substrate, it is more preferable due to having good surface polarity and also easily commercially available of high quality. When HgCdTe epilayer is grown directly on the GaAs substrate, there exist some dislocations in the epilayer due to large lattice mismatch between HgCdTe and GaAs substrate.The CdTe semiconductor is grown like a buffer layer to reduce dislocation in the HgCdTe epilayer grown on GaAs or other alternative substrate [1].The crystal quality of CdTe buffer layer directly affected HgCdTe epilayer. Therefore, CdTe needed to be low defect density.Because of %14.6 lattice mismatch between CdTe and GaAs [2], some defects are observed in CdTe buffer layer. ZnSe epilayer can be used to decrease lattice mismatch between CdTe and alternative substrate. When ZnSe interlayers are grown with high quality, CdTe affects positively. The aim of this theses is the growth of ZnSe epilayer films on (211) GaAs substrates by molecular beam epitaxy (MBE). The effect of growth temperature, VI/II flux ratio and deoxidation process with In and As were studied in this study. Crystal qualities of films were investigated by using X-ray diffraction. The surface morphology of ZnSe films were analyzed by atomic force microscopy and Nomarski microscopy. Vibrational phonon modes, thermal and elastic strains of ZnSe epilayer were observed by using Raman spectroscopy.Master Thesis Characterization of Lattice Mismatch Induced Dislocations on Epitaxial Cdte Films(Izmir Institute of Technology, 2015) Bilgilisoy, Elif; Selamet, Yusuf; Bilgilisoy, Elif; Selamet, Yusuf; 01. Izmir Institute of Technology; 04.05. Department of Pyhsics; 04. Faculty of ScienceMercury Cadmium Telluride (HgCdTe) is a widely used material for infrared focal plane array applications. In order to produce high quality infrared detecting material, HgCdTe needs to be grown on large area alternative substrates such as GaAs, GaSb, Si or Ge. GaAs is the best choice as an alternative substrate due to its surface polarity and commercially availability of high quality epi-ready wafers. However, there exists a lattice mismatch between HgCdTe and GaAs. To minimize the detrimental effect of the large lattice mismatch between the two materials, Cadmium Telluride (CdTe) is preferred as a buffer layer for HgCdTe IR material. The lattice mismatch between HgCdTe/CdTe and the GaAs substrate results in a large number of misfit dislocations. Dislocation density of the buffer layer limits and reduces the detector device performance. For this reason, the crystal quality and dislocation analysis of CdTe are examined in detail to produce large area and high performance HgCdTe IR devices. The aim of this thesis is the characterization of lattice mismatch induced dislocations on epitaxial CdTe buffer layers. CdTe epilayers which were grown on (211)B GaAs by molecular beam epitaxy (MBE) were subjected to two different etch treatments to quantify the crystal quality and dislocation density. The crystal quality was also obtained by using x-ray diffraction (XRD) measurements. The thicknesses of the samples were measured by ex-situ spectroscopic ellipsometry (SE). The surface morphologies of the CdTe buffer layers were analyzed by atomic force microscopy (AFM), scanning electron microscopy (SEM) and Nomarski microscopy before and after wet chemical etching. Vibrational phonon modes distributions of the as-grown and etched samples were examined by Raman spectroscopy mapping. The “triangle” and “trapezoid” shaped etch pits were compared due to the Everson and Nakagawa etching solutions, respectively. Measured etch pit density (EPD) values of “triangle” etch pits were found in 0.3x108 – 3.8x108 cm-2 range and “trapezoid” shaped etch pits were found in 0.03x108 – 0.6x108 cm-2 range for samples.