Growth, thermal and spectral properties of Nd-doped NaGd(MoO4)2 crystal

Nd³⁺-doped NaGd(MoO₄)₂ crystal with dimensions were grown by Czochralski method. Nd³⁺:NaGd(MoO₄)₂ crystal melts at 1182 °C. The hardness of Nd³⁺:NaGd(MoO₄)₂ crystal is 334 VDH. The specific heat is 72.6 cal/mol K. The thermal expansion coefficients are for c-axis and for a-axis, respectively. The absorption cross-sections of Nd³⁺:NaGd(MoO₄)₂ crystal are with a FWHM of 9 nm at the 804 nm for π-polarization and with a FWHM of 17 nm at 807 nm for σ-polarization, respectively. The emission cross-section σ_em are at 1063 nm for π-polarization and 1.94×10^-20 at 1070 nm cm² for σ-polarization, respectively. The fluorescence lifetime τ_f is 93.9 μs at room temperature.     

Growth and characterization of pendeo-epitaxial GaN on 4H–SiC substrates

Growth on AlN/4H–SiC substrates of coalesced, non-polar GaN films having volumes of material with reduced densities of dislocations and stacking faults has been achieved from etched stripes via the statistical and experimental determination of the effect of temperature and V/III ratio on the lateral and vertical growth rates of the GaN{0 0 0 1} faces combined with pendeo-epitaxy. AFM of the uncoalesced GaN(0 0 0 1) and GaN vertical faces revealed growth steps with some steps terminating at dislocations on the former and a pitted surface without growth steps, indicative of decomposition, on the latter. Coalescence was achieved via (a) a two-step route and the parameters of (1) and V/III=1323 for 40 min and (2) 1020 °C and V/III=660 for 40 min and (b) a one-step route that employed and a V/III ratio=660 for 6 h. The densities of dislocations in the GaN grown vertically over and laterally from the stripes were 4×10¹⁰ cm⁻² and 2×10⁸ cm⁻², respectively; the densities of stacking fault in these volumes were 1×10⁶ cm⁻¹ and 2×10⁴ cm⁻¹, respectively. The defects in the wing material were observed primarily at the bottom of the film where lateral growth of the GaN occurred from the AlN and the SiC. Plan view AFM also revealed different microstructures and a reduction in the RMS roughness values from 1.2 to 0.95 nm in these respective regions.     

Synthesis, growth and characterization of nonlinear optical crystal: l-tyrosine hydrobromide

l-tyrosine hydrobromide (l-THB) a semi organic nonlinear optical material with molecular formula C₉H₁₂NO₃Br has been synthesized at ambient temperature. Spectral, thermal and optical techniques have been employed to characterize the new material. The solubility of l-THB at varying temperatures was determined in different concentrations of hydrobromic acid. Bulk single crystals of size 15×7×4 mm³ of l-THB were grown by slow evaporation method at constant temperature. Powder X-ray diffraction pattern of the grown l-THB has been indexed. Functional groups present in the sample were identified by FTIR spectral analysis. Chemical composition of the synthesized material was confirmed by carrying out CHN analysis. Thermal stability of l-THB was determined from TGA/DTA and DSC response curves. Mechanical hardness of the grown crystal l-THB was determined and Vickers hardness number was calculated. The Kurtz powder second harmonic generation test shows that the compound is a potential candidate for optical second harmonic generation. The optical transparency range and the lower cut-off of UV transmission were identified from the recorded UV-vis spectrum of l-THB. The optical energy gap of l-THB is 3 eV.     

Growth of single crystals of the new double perovskite Ba2HoRu1−xCuxO6 from high temperature solutions

Single crystals of Ba₂HoRu_1−xCu_xO₆ have been grown from high temperature solutions using PbO–PbF₂ as solvent in the temperature range 1150–1250 °C. Crystals with a six sided plate like morphology measuring up to 3 mm across and 0.5 mm thick and polyhedral habit measuring up to 2 and 1 mm in thick mass were obtained. Powder X-ray diffraction patterns obtained on the crystals were indexed to give a monoclinic space group P2₁/n with lattice parameters a=5.875(2), b=5.874(3), c=8.960(1) and β=89.995(2)°. The crystals with x=0 show a single anomaly at 6.5 K corresponding to an antiferromagnetic phase with . The crystals containing Cu show additional anomalies at 18 and 48 K. The SEM and EDS analysis reveals a 2116 phase.     

Oriented growth of large size calcium fluoride single crystals for optical lithography

We report (1 1 1), (1 1 0) and (1 0 0) growth of CaF₂ by the vertical Bridgman method. Crystals up to 250 mm diameter were grown and various growth parameters such as growth rate, temperature gradient and post-growth cooling rate were studied. It was found that the growth rate and the cooling rate are slower for the larger diameter crystals with a fixed temperature gradient. These growth parameters were optimized for growing the crystals along specific orientation after realizing that CaF₂ has a tendency to grow along an orientation close to 1 1 0. Degradation in optical transmittance was evaluated by irradiating the crystal to γ-rays up to a dose of 10⁵ rad. Optimized scavenger addition resulted in crystals with better radiation resistance and excellent VUV transmittance.     

Boron segregation control in silicon crystal ingots grown in Czochralski process

Boron-doped silicon single crystals of 207 mm diameter with various growing conditions are grown from a large amount of the melt in the cusp-magnetic Czochralski method, and the effects of growing parameters on dopant concentrations in the crystals are experimentally investigated. Equilibrium distribution coefficient of boron calculated by BPS model is 0.716. With the crystal rotation (ω) of 13 rpm and the crucible rotation of , the effective distribution coefficient (k_e) is 0.751 in zero magnetic strength and increases up to 0.78 in the magnetic strength of 640 G. For , there is no significant influence of ω on k_e. With , k_e is almost unity. The experimental results are compared with theory.     

Kinetics of dopant incorporation in GaAs grown by organometallic vapor-phase epitaxy

A diffusive capture reaction of dopant atoms by relevant host atoms, via the Rideal–Eley mechanism, in GaAs grown by organometallic vapor-phase epitaxy is shown to result in the dopant concentration in the crystal acquiring a dependence on p_Ga (which is proportional to the growth rate) in agreement with data on S_As, Zn_Ga, and Si_Ga where p_Ga is the partial pressure of trimethylgallium in the input gas stream.