In the present review, various crystal growth methods are reviewed from the viewpoint of crystal growth of high-quality large CdTe and CdZnTe crystals. The VGF (Vertical Gradient Freezing) method is now becoming the most appropriate one for growing large single crystals. 100mm diameter CdZnTe twin-free single crystals have been first realized by a precisely temperature controlled VGF method. The crystal quality of these single crystals have been evaluated by Nakagawa etchant and by a four-crystal monochrometer X-ray diffraction method and the quality was found to be of high-quality as substrates for MCT epitaxial growth. The relationship between the Cd reservoir temperature and the precipitate size is discussed from the viewpoint of nonstoichiometry. The future perspectives of CdTe crystals are discussed.
We have developed VCZ method for growing GaAs and InP single crystals with low-dislocation-density. In this report, we show the growth by the VCZ method and the characterization of 4"φ and 6"φ semi-insulating and 3"φ Si-doped GaAs single crystals. In the VCZ method, a GaAs crystal is pulled under an arsenic atmosphere sealed in an inner chamber. The surface of the crystal isn't decomposed over 1100℃, therefore the crystal can be grown under a low tempertaure gradient so that growing a crystal with low dislocation density can be achieved. Dislocation densities of 4"φ and 6"φsemi insulating VCZ crystals are one order of magnitude and one third lower than that of the 4"φ LEC crystal respectively. The VCZ crystal includes low residual stress which causes cracking of a wafer and generating slip-dislocations in a wafer during hest treatments. In our heat treatment of 4"φ LEC and 4"φ VCZ wafers at 480℃, slip-dislocations are generated only in the LEC wafer. We have also successfully grown 3"φ Si-doped GaAs single crystals with wide dislocation free region by the VCZ method.
High quaity ZnSe single crystals have been grown by a vapor phase transport method (modified Prior method), using a commercial grade high purity selenium and the zinc purified by vacuum distillation and overlap zone-melting. Photoluminescence and photoexcited cyclotron resonance studies confirm that the qualty of the grown crystals is very high. The donor concentration of the purest crystal is 4×10^<14>cm^<-3> and the cyclotron mobilities at 4.2K of electrons and heavy holes are 470,OOO and 21,000cm^2/V・s, respectively. A new emission related to twin boundaries is observed at 2.8002 eV, the intensity of which is proportional to the 1.2 power of the excitaion intensity.
ZnSe-based heteroepitaxial crystals are grown on III-V substrates, mainly on GaAs, because II-VI wafers with high quality and large area are hardly obtained. The heteroepitaxial crystals include two-dimensional elastic strains due to mismatches of lattice constant and thermal expansion coefficient. The strains in ZnSe layers on GaAs substrate measured with X-ray diffraction are described as a function of temperature for different layer thicknesses. The stress at the heterointerface is also estimated from energy shift of Cr^<2+> luminescence in GaAs substrate. The two-dimensional strain changes symmetry of the crystal lattice and energy band structure. The band structure of strained layers are studied by low-temperature reflectance spectra. The electrical properties of ZnSe/GaAs hetero-interface and influences of substrate-surface treatment are also discussed.
A three-dimensional finite element computer program for thermal stress analysis was developed for cracking of trigonal class 3m bulk single crystals such as lithium niobate (LN) during Czochralski growth. A tensor transformation technique was used to obtain an elastic constant matrix and a thermal expansion coefficient vector corresponding to an arbitrary pulling direction. The anisotropy of elastic constants and thermal expansion coefficients as well as their temperature dependence was considered in the program. Using this program. we analyzed thermal stress in a LN single crystal. The analyses were carried out, for the pulling directions of both the α-axis  and the c-axis. The results show that thermal stress is lower in the c-axis pulling than in the a-axis pulling. The relation between thermal stress and the cracking and quality of a bulk single crystal was also discussed.
Short wavelength light generation is a trend in a field of applications of laser such as information process, material processing and laser fusion. The energy driver at nuclear fusion experiments required an efficient generation of short wavelength light with a partially coherency for irradiation uniformity improvement. The partially coherent light has wide spectral width and large beam divergence of which the hamonic conversion efficiency is greatly degraded. An arrowance of the spectral bandwidth of the lowly deuterated KDP crystal is estimated larger than that of the KDP or highly deuterated KDP. It was found that the deuterated ratio of the grown crystal was lower than that of the growth solution and the distribution coefficient of deuterium decreased with decreasing of deuterated ratio of the growth solution. The distribution of deuterated ratio in the grown crystal was shown constant within the measuremental error. It was also demonstrated that 10 cm class 13% KD^*P crystals were grown very easily.
Molecular recognition and cystallization processes are investigated using nickel complex (NI-complex) as a host, and 1-and 2-methylnaphthalene as guests. Information of clathrate crystals, guest molecules are recognized by a host with characteristic host-guest interaction in solutions and/or on the growing surface of the crystals, then the guest molecules are included in the host lattice. Such molecular recognition and integration of host-guest structure are performed through the nucleation and crystal growth processes. In this work it was observed that the species crystallizing out (polymorphs) and selection of guest molecule are mainly determined by nucleation process and the behaviors are strongly influenced by the condition of the circumstance, i. e. temperature and guest molecular concentration in solutions. On the other hand, the transformation proceeds between the polymorphous clathrate crystals, accompanying the exchange of guest molecules due to the difference of thermodynamic stability of the crystals. The mechanism of the competitive crystallization and the transformation of polymorphs could be explained quantitatively by estimating the supersaturation degree of each polymorph and the thermodynamic stability of the host lattice structure, from the solubility of each host lattice of the polymorphs.