HgCdTe (MCT) infrared (IR) photodetectors have been used for various military and civilian applications including thermal imaging, medical imaging, and astronomy. These detectors are commonly fabricated on MCT layers grown on a foreign substrate epitaxially using delicate growth techniques such as Molecular Beam Epitaxy (MBE). The crystal quality of epitaxial layers grown on a substrate critically depends on the quality of the substrate. One of the stringent requirements in choosing the substrate material is the lattice match between grown layer and the underlying substrate. With perfectly matching lattice structure, CdZnTe has been the major substrate material for the MCT growth. The production of defect free single crystal CdZnTe bulk crystal has then attracted great attention among the research and industrial community of MCT based photodetectors. This thesis focuses on the growth and characterization of Cd1-xZnxTe crystals with the main objective of obtaining high-quality, CZT bulk crystal with large crystal sizes. To be compatible with the subsequent MCT growth, we aimed to obtain Cd0.96Zn0.04Te crystals with (211) crystal surface orientation. CdZnTe bulk crystal growths were performed in three-zone vertical Bridgman furnace by a high temperature melt process called &ldquo / Modified Bridgman Technique&rdquo / . Difficulties in both growth and characterization are presented and discussed in this report. Characterization of the grown CdZnTe crystal was performed to determine the crystallographic orientation, crystal quality, Zn distribution, IR transmission, resistivity, polarity, etch pit density, and surface properties. For this purpose, electron microscopy with analytical diagnostic tools like EDS and EBSD, XRD, optical transmission spectroscopy, and electrical measurement systems have been employed. We demonstrated the successful growth of single crystal CZT crystals using our simple Bridgman furnace. Physical properties of the grown crystal were very promising and encouraging for future applications. Crystal pieces having sizes larger than 5 x 5 mm2 with uniform Zn distribution and (211) surface orientation were obtained. IR transmission of nearly 60% which is as good as that of the commercial substrates was achieved. The electrical resistivity was much better (higher) than generally accepted values. However, the XRD results indicated the presence of defects and/or micro grains in the bulk crystal. These structures seemed to have prevented obtaining good FWHM values, which are the measure of crystal quality, in the XRD analysis.

Im Rahmen dieser Arbeit wurde der pseudo-halogenide Gasphasenepitaxie (PHVPE)-Prozess für die GaN-Kristallzüchtung entwickelt. Dieser Prozess basiert auf dem Zyanid als Transportmittel für Ga. Das HCN wurde aus der Reaktion von heißem NH3 entweder mit Graphit oder einem gasförmigen Kohlenstoffträger gewonnen. Als Quelle für reaktiven Stickstoff diente NH3. Im ersten Ansatz wurde ein Reaktor aus Graphit genutzt. In diesem Fall wurden Wachstumsraten von 60 um=h erreicht. Außerdem zeigte der Kristall eine geringe Perfektion mit hoher V-Grubendichte. Im zweiten Ansatz bestand der Reaktor aus mit pyrolytischem Graphit beschichteten Teilen. Diese Änderung des Konzeptes half die Kristallqualität zu verbessern, reduzierte aber gleichzeitig die Wachstumsrate drastisch, weil das Ga-transportmittel nicht mehr ausreichend zur Verfügung stand. Der neu konstruierte, graphitfreie Aufbau stellt den dritten Zugang zur PHVPE dar. In diesem Fall entsteht HCN während eines Degussa-Prozesses am Pt-Katalysator im Züchtungsreaktor. Zur Untersuchung der Reaktionswege wurde ein FTIR-basiertes insitu Abgasmesssystem entwickelt. GaN-Kristalle wurden auf Saphir und Ga2O3 Substraten, AlN/Al2O3 und GaN/Al2O3 Templates gezüchtet. Eine Selbstseparation wurde für dicke GaN-Schichten auf Ga2O3 erreicht. Die Proben wurden mit verschiedenen Methoden charakterisiert, z.B. mit der Röntgenbeugungs-Spektroskopie (XRD) und Elektronenrückstreubeugung (EBSD) für die Kristallperfektion und kristallographische Orientierung, der Transmissionselektronenmikroskopie (TEM) zur Untersuchung von Versetzungen und der Grenzfläche zwischen GaN und dem Ga2O3, der Rasterelektronenmikroskopie (REM) für die Oberflächenmorphologie und Schichtdicke, der energiedispersiven Röntgenspektroskopie (EDX) für die Kristallzusammensetzung, sowie der ex-situ und in-situ Abgasanalyse mit der Fourier-Transform-Infrarotspektroskopie (FTIR) zum Studium der Reaktionswege. / Within the frame of this work the pseudo halide vapor phase epitaxy process (PHVPE) was developed for GaN crystals growth. The process is based on cyanide as a transport agent for Ga. The source of HCN was the reaction of hot NH3 with either graphite or gaseous carbon precursor. Source of reactive nitrogen was NH3. In the first approach the reactor made of graphite was used. In this case growth rate of 60 um/h was achieved. Additionally, the crystals exhibit poor quality with high V-pit density. The second approach was to provide the reactor with pyrolytical boron nitride covered parts. Changing the concept helped to improve the crystals'' quality but simultaneously reduced drastically the growth rate, due to the lack of sufficient supply of Ga transport agent. Newly designed graphite free setup is used in the third approach for PHVPE. In this case, HCN forms during Degussa process on Pt catalyst, inside the growth reactor. For investigation of the reaction paths, an in-situ exhaust gas measurement system based on FTIR was developed. GaN crystals were grown on sapphire and Ga2O3 substrates, AlN/Al2O3 and GaN/Al2O3 templates. Self separation was achieved for thick GaN crystals grown on Ga2O3. The samples were characterized by various methods i.e. x-ray diffraction spectroscopy (XRD) and electron back scattering diffraction EBSD for crystal quality and crystallographic orientation, transmission electron microscopy (TEM) for investigating dislocations and interface between GaN and Ga2O3, scanning electron microscopy (SEM) for surface morphology and layer thickness, energy dispersive x-ray spectroscopy (EDX) for crystals compositions, ex-situ and in-situ exhaust gas analysis by Fourier transform infrared spectroscopy (FTIR) for investigation of the reaction paths.