CsLiB_6O_<10>(CLBO) crystals are superior in fundamental properties for the generation of UV light by frequency conversion. For high power UV light generation, it is necessary to develop technique for growing high-quality single crystals in order to prevent laser damage and thermal dephasing induced by UV light absorption. We have attained improvement of crystal quality by a newly developed melt stirring technique of highly viscous CLBO growth melt. By this mean, bulk laser induced damage threshold of CLBO have been improved by 2.5-fold as compared to crystals grown from melt without stirring. Further, self-heating generated by the absorption of UV light was also reduced. These improvements were due to the reduction of dislocation density in CLBO crystals. Mechanical properties such as Vickers hardness were also enhanced. As a result, we have obtained stable fourth harmonic generation of Nd:YAG laser (266 nm light) at an average power of 20 W for 100 hours continuously.
High performance silicon (Si) thin film transistors (TFTs) on non-alkali glass substrate will be key to achieving a system on glass (SOG). However, it is very diflicult to form high performance Si devices on glass substrate, because glass is an amorphous materials and its deformation temperature is low: 600℃. Excimer laser crystallization is a useful technique for forming high-quality Si film on glass substrate. However, the obtained Si film is a polycrystalline material with small grains and the reproducibly obtained mobility of TFT is about 150 cm^2/V・s. This value is insufficient to achieve a SOG. We thus need a singlecrystalline-Si film on glass substrate. Since TFTS are positioned at different sites on glass substrate and it is very difficult to form single-crystalline-Si over a wide area, a self-aligned formation of single-crystalline-Si in the channel regions of the TFTS is necessary. In this paper, we propose new Si growth methods to achieve self-aligned formation of single-crystalline-Si in the channel region of TFTS on glass substrate.
Studies on the Na flux method for GaN single crystal growth were reviewed. Platelet single crystals of hexagonal wurtzite-type GaN (h-GaN) with a size of about 1 mm were obtained at 650-850'C in a stainless-steel sealed tube using NaN_3 as a source of Na and N_2. A mixture of h-GaN and cubic zinc-blend-type GaN (c-GaN) grains was precipitated at the bottom of a BN crucible at 570℃. Platelet h-GaN single crystals with a size over 5 mm in the longest direction grew at 750℃ and a constant N_2 pressure of 5 MPa for 200-450 h by introducing N_2 from the outside of a stainless steel container. Colorless transparent prismatic h-GaN single crystals of about 1 mm were obtained at a lower Na content in the starting Na-Ga melt. A carrier concentration n-type of 1-2×10^<18>cm^<-3> and a mobility of 100 cm^2 V^<-1>s^<-1> were measured at room temperature for platelet crystals of about I mm. The full-width at half-maximum (FWHM) of the rocking curve measured for 0004 X-ray diffraction peak was 25-32 arcsec.
Low-dislocation-density large-diameter GaAs single crystals have been strongly required. We have developed dislocation-free 2-inch to 3-inch Si-doped GaAs single crys-tals, and low-dislocation-density 4-inch to 6-inch semiinsulating GaAs single crystals by vertical boat (VB) method. Such low-dislocation-density large-diameter single crystals could be grown by achievement of the flat solid-liquid interface during the crystal growth. We confirmed that low-residual-strain VB substrate have higher resistance against slip-line generation during MBE process. VB-GaAs crystals showed uniform radial profile of resistivity, due to uniform radial profile of carbon concentration reflecting to the flat solid-liquid interface. Uniformity of micro-resistivity of a VB-GaAS substrate was much better than that of a LEC-GaAS Substrate, which is thought that the concentration of excess arsenic atoms inside the cell of dislocations is higher in VB crystals than in LEC crystals.
Growth hillocks and single steps were studied in situ by laser interferometry and atomic force microscopy on the (101) KDP face. The hillock is transformed from the rounded to the triangular, nearly fully polygonized, shape when the supersaturation rises. This indicates non-linear dependence of the average step rate for at least several step orientations. AFM studies of a single step though at much lower growth rate, showed that the roughening width of a step shrinks from 〜10μm at the step growth rate 0.14 nm /s to〜4μm at 7 nm/s. We believe both phenomenas occur because fluctuations are not fast enough to provide sufficient kink density. This is believed to happen because the rate at which fluctuations create kinks is finite and nearly supersaturation independent near equilibrium while the annihilation rate of kinks during growth increases with supersaturation. Examples concerning growth induced three dimensional faceting are mentioned.