Improved vertical Bridgman growth techniques for various kinds of single crystal are introduced and discussed. In the first, compound semiconductors of GaAs and InP are grown by the liquid encapsulated vertical Bridgman growth technique, using pyrolytic boron nitride crucibles, and the role of liquid boric oxide (B_2O_3) is discussed from the viewpoints of the single crystal growth and the elimination of dislocations. In the second, various kinds of oxide crystals, such as LiNbO_3, La_3Ga_5SiO_<14>, La_3Ta_<0.5>Ga_<5.5>O_<14,> and KNbO_3, are grown by the vertical Bridgman growth technique using platinum crucibles, and the problems of adherence between the crucibles and crystals grown in them are discussed. In the third, α-Al_2O_3 (sapphire) and α-Al_2O_3/YAG:Ce eutectics are grown by the vertical Bridgman growth technique using iridium, molybdenum and tungsten crucibles, and the linear thermal expansion coefficients of the crystals grown and the crucibles used are discussed from the viewpoint of crystal release from the crucible and reuse of the crucible.
White light-emitting diodes (wLEDs) are the new environmental friendly sources for general and specific lighting purposes. Although their commercialization is extending rapidly, current wLEDs cannot be used in applications that require high-brightness due to overheating, which drastically decreases their emission efficiency, color quality and lifetime. This paper reviews the recent investigations on single-crystal phosphors (SCPs) as alternative to conventional ceramic powder phosphors (CPPs). SCPs represent a totally new approach, that can overcome all the difficulties of CPPs. SCPs can realize resin-free, all-inorganic packaging, thus allowing the use of high-power LEDs and LDs. Further, it is demonstrated that in comparison with CPPs, SCPs exhibit an outstanding conversion efficiency and thermal stability up to 300℃. Ce:Y_3Al_5O_<12> SCPs are suitable for neutral white light sources, where a high light intensity is required independently of the color quality. On the other hand, it is shown that Ce:(Y_<1-x>Lu_x)_3Al_5O_<12> SCPs, in combination with an additional red phosphor, are adequate to realize warm and neutral trichromatic white light sources with a color rendering Ra > 90.
Gallium Oxide is attracting attention as a new material for optical and electrical applications. It has a large band gap of 4.8 eV. The electron concentration can be controlled in a range between 10^<16> cm^<-3> and 10^<19> cm^<-3>. Large-size bulk crystals can be obtained easily because melt growth is possible under the atmospheric pressure. From these material features, we expect high performance and low production cost of LEDs and high power devices. In this report, we introduce the properties of β-Ga_2O_3 single crystal substrates and the present status of device development.
We demonstrate the high-speed growth of (2^^-01)-oriented β-Ga_2O_3by halide vapor phase epitaxy, and the orientation control of the β-Ga_2O_3 layers by using off-angled sapphire (0001) as the substrates.The β-Ga_2O_3 layers were grown using GaCl and O_2 as source gases. The growth rate monotonically increased with increasing the partial pressures of the source gases, reaching over 250 μm/h. X-ray pole figure measurement of a β-Ga_2O_3 layer grown on a sapphire (0001) substrate with no off angle indicated the presence of six inplane rotational domains, in accordance with the substrate symmetry, and some minor (310) domains. By using off-angled substrates and thick layer growth, one of the in-plane orientations was strongly favored and the incorporation of the (310) domainswas effectively suppressed. These results showthatthe HVPE technique is promising for the growth of β-Ga_2O_3 layers for the cost-effective production of β-Ga_2O_3 based devices.
Growth processes occurring in Physical Vapor Transport (PVT) method for SiC single crystals are described in view of quasi-equilibrium phase transitions. Si-C binary phase diagrams are found to be successful in giving a consistent explanation for sublimationrecrystallization phenomena under appropriate assumptions. In particular, technical directions obtainable from thermodynamic descriptions of the PVT will be quite useful when growth conditions have to be optimized for realizing SiC crystals with higher crystallinity upon suppressing unwanted perturbations such as foreign phase precipitations. In order to establish more semi-quantitative views of the PVT mechanism, the thermodynamic description proposed so far has to include the effects of reactions between vapors and other graphite constituents existing inside crucibles such as graphite crucible walls or particles formed after thermal decomposition of SiC source powders.
Currently,Tb_3Ga_5O_<12>(TGG) single crystal is used as Faraday rotator in the laser machinery whose wavelength is <1100nm. However, TGG have problems of such as low Faraday rotation angle, difficult crystal growth,high cost, and so on. In order to overcome these problems, we focused on Tb_3(Sc,Lu)_2Al_3O_<12>(TSLAG) single crystal. The optical and magneto-optical properties of the TSLAG crystal are analyzed in detailed and compared with those of the reference compound TGG. TSLAG presents a very low absorption coefficient, particularly lower than that of TGG in the visible region, and its Verdet constant is 20% larger at any wavelength. To achieve cost reduction, we tried to grow large TSLAG single crystal. At initial experiments, TSLAG was cracked by the internal stress of the crystal, and thermal stress. By optimizing the growth conditions, TSLAG single crystal was successfully grown with 2.0 inch in diameter. We has realized an optical isolator using TSLAG single crystal for the first time.