This paper is devoted to the use and further development of the single crystal growing technique invented by Professor Jan Czochralski (1885-1953). The possibilities of the Czochralski technique are demonstrated. Further improvements were introduced at the Scientific Research Company "Carat" (Lviv, Ukraine) to grow large size complex oxide single crystals. The paper presents an overview of some single crystals grown with the use of a modified technology. Growth parameters and properties of resulting crystals are summarized to show a high potential of the Czochralski technique as an industrial technology to grow large-size, high quality, and structurally perfect single crystals of complex oxides.
Crystal growth from the solution under high N_{2} pressure (HNP method) results in high quality mm size crystals of GaN in 5 to 24 hour process. The crystallization of AlN is less efficient due to relatively lower solubility of nitrogen in the liquid Al. Possibility of InN growth is strongly limited since this compound is unstable at T > 600°C even at 20 kbar. The growth of cm size high quality GaN crystals requires lower supersaturations and longer processes.
Single crystals of Cd_{1-x}Co_xTe and Cd_{1-x-y}Co_xMn_yTe are characterized with X-ray powder diffraction and electron microprobe to establish compositional dependence of the lattice parameters and deduce Co solubility limit. The experimental compositional profiles are examined on specimens taken from various locations of ingots along their longitudinal axes and compared with normal freezing distributions. The values of Co segregation coefficient are analyzed for both ternary and quaternary alloys in terms of normal freezing mode.
We present results of investigation on growth of solid solution crystals with perovskites and K_2NiF_4 structures used as substrates for epitaxy. Perovskite single crystals with no twins and crystals with K_2NiF_4 structure with the lattice parameter in the range 3.876-3.819Å and 3.754 to 3.688Å, respectively, can be grown. Here preliminary results on investigation on growth of other solid solution crystals with the lattice constant from 3.946 to 3.688Å are also presented thus covering the whole interesting range for depositing oxide materials. These crystals can be grown by the Czochralski method that secures their high structural quality. Discussed crystals are resistant to reaction with the deposited oxide layers.
Today, the technology of typical silicon-solar cells is fully developed and mature. In spite of its continuous improvements, the record efficiencies of 25.0% are approaching theoretical solar conversion limits of around 33.7%. Values much beyond this limit are likely to be achieved using III-V semiconductor compounds, electrical and optical properties are more suitable for solar energy conversion. They are the most promising candidates for realizing solar cells, which can achieve efficiencies of 50% and more. In this paper we studied the influence of pressure in the reactor chamber on the roughness of an InGaP "nucleation layer" grown on Ge. The growth of the layers was performed in a metalorganic vapour phase epitaxy reactor AIX 200/4. The source gases were trimethylgallium, trimethylindium and AsH_3. The rate of pressure in the reactor was raised from 100 mbar to 400 mbar by 50 mbar. The InGaP layers with the lowest roughness were achieved at the pressure of 400 mbar. The layers were characterized by very low roughness (RMS < 0.3) measured by atomic force microscopy. The quality of the surface was perfect enough to be applied in a solar cell structure.
The results obtained with the use of the pressure grown GaN single crystalline substrates allow to draw the following conclusions important for the construction of In-free UV light emitting diodes and lasers and InGaN-based high power blue lasers: 1. The application of the pressure grown GaN single crystalline substrates allows to grow near dislocation free layer structures by both metal organic chemical vapor deposition and MBE. 2. The elimination of dislocations leads to highly efficient UV emission from GaN and GaN/AlGaN quantum wells which is impossible for strongly dislocated structures grown on sapphire. 3. At high excitations (i.e. in lasers) dislocations are effective nonradiative recombination centers also in the InGaN containing structures, therefore the elimination of these defects is crucial for better performance of blue lasers. 4. The analysis of microstructural and optical properties of the InGaN containing dislocation free structures shows that the main mechanisms of carrier localization in InGaN are not related with the nm scale compositional fluctuations in InGaN. In the paper, the optical and structural properties of the near dislocation free GaN-based structures leading to the above conclusions are discussed.
ZnO thin films were grown by atomic layer deposition method at extremely low temperature using a reactive diethylzinc as a zinc precursor. Optical properties, electrical properties and surface morphology were examined by photoluminescence, Hall effect and atomic force microscope. The study shows correlation between optical, electrical properties and surface morphology in a series of samples of different thickness.
Crystal-melt interface was investigated during Czochralski growth of SrLaGaO_{4} and SrLaAlO_{4} crystals on ⟨001⟩ oriented seeds. Relations between the ratio of the core diameter, grown on (001) plane, and the crystal diameter, as a function of seed rotation speed were determined. It was confirmed that it is possible to control the core diameter during the crystal growth. A new module was introduced into the crystal growth controlling program. It enables to estimate the surface tension coefficient between crystal and melt at the beginning of crystallization. This value is then used to compute proper corrections for automatic weighting system.
Thin films of MnO_2, Mn_2O_3, and Mn_3O_4 have been grown from single precursor solution by varying the post-annealing condition on the glass and corning substrate using a sol-gel technique. By annealing in air and at temperature between 600 and 800°C, cubic Mn_2O_3 films could be formed. The films were thermally annealed at different temperatures between 300 and 800C to create different crystalline structure. Even under the air-annealing condition, Zn doping results in a structural transformation from cubic Zn_{x}Mn_{2-x}O_3 to tetragonal Zn_{x}Mn_{3-x}O_4. X-ray diffraction, atomic force microscopy, and UV-visible spectra were used to characterize the effect of thermal annealing on the optical and structural properties of a Zn doped manganese oxide thin film. Optical properties of the Mn_2O_3 and Mn_3O_4 films have been investigated by pointwise unconditioned minimization approach.
Due to high bonding energy of N_2 molecule, the III-V semiconducting nitrides, especially GaN and InN require high N_2 pressure to be stable at high temperatures necessary for growth of high quality single crystals. Physical properties of GaN-Ga(l)-N_2 system are discussed in the paper. On the basis of the experimental equilibrium p-T-x data and the quantum-mechanical modeling of interaction of N_2 molecule with liquid Ga surface, the conditions for crystallization of GaN were established. The crystals obtained under high pressure are of the best structural quality, having dislocation density as low as 10-100 cm^{-2} which is several orders of magnitude better than in any other crystals of GaN. The method allows to grow both n-type substrate crystals for optoelectronics and highly resistive crystals for electronic applications. The physical properties of the pressure grown GaN measured to characterize both point defects and extended defects in the crystal lattice are discussed in the paper. A special attention is paid to the application of high pressure to reveal the nature of the point defects in the crystals and electric fields in GaN-based quantum structures. Due to their very high structural quality, the pressure grown crystals are excellent substrates for epitaxial growth of quantum structures. It opens new possibilities for optoelectronic devices, especially short wavelength high power lasers and efficient UV light emitting diodes. This is due to the strong reduction in dislocation densities in relation to existing structures (10^6-10^8 cm^{-2}) which are grown on strongly mismatched sapphire and SiC substrates. The experimental results on the epitaxial growth and physical properties of GaN-based device structures supporting above conclusions are discussed in the paper. The current development of blue laser technology in High Pressure Research Center is shortly reviewed.
Gallium antimonide (GaSb) single crystals were grown by modified Czochralski method integrated with in situ synthesis in a flowing atmosphere of pure hydrogen. The influence of charge material purity as well as other technological parameters on GaSb crystals quality was investigated. High purity undoped GaSb single crystals were grown with residual acceptors concentration < 1.4 × 10^{17} cm^{-3} and high mobility ≈ 690 cm^2/Vs (at 300 K). P-type GaSb crystals were doped with silicon (carrier concentration up to 2 × 10^{19} cm^{-3}) and with zinc (up to 1 × 10^{19} cm^{-3}). Tellurium doped n-type GaSb single crystals were obtained with concentration up to 2 × 10^{18} cm^{-3}. Electrical parameters were investigated by the Hall measurements (300 K and 77 K). Temperature dependent Hall measurements (10 ÷ 300 K) were used to compare the quality of undoped GaSb (obtained from Sb of different purity). Dopant concentration was estimated by glow discharge mass spectroscopy analysis. Axial and radial distribution of carrier concentration were investigated especially for Te-doped crystals (low segregation coefficient of Te in GaSb). Great contribution of compensation and self-compensation mechanisms is shown especially for the beginning part of grown crystals and for low Te-doping level. Radial distribution of physical properties for crystals grown in 〈100〉 direction is not axisymmetrical especially for doped GaSb crystals.
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