Journal of Crystal Growth最新文献

Short Step-Bunching (SSB) are a kind of linear defects consisting of convex and concave undulations on the surface of 4H-SiC homoepitaxial layer. In this work, we report the characterizations of SSBs on 12 μm, 50 μm and 85 μm thick SiC epilayers by using optical microscopy (OM), micro-photoluminescence spectra (PL), atomic force microscopy (AFM), chemical mechanical polishing (CMP), molten KOH etching (10 min, 500 ℃) and high resolution transmission electron microscope (HRTEM). It is found that these SSBs are 200 ∼ 250 μm long, perpendicular to the step-flow [11], [12], [13], [14], [15], [16], [17], [18], [19], [20] direction, leading to local rugged surfaces of epilayer. No other poly-types are identified on and around these SSBs. H₂ etching the substrate reveals the existence of short-line defects on the substrate with one or more dislocations (TSD or TED) or an amorphous bump locating in center of most of them. Presumably, the amorphous bump was a kind of carbon inclusion. Based on the above results, we proposed that the SSBs develop from the short-line defects generated when etching the substrates prior to epilayer growth. Elimination of short-line defects by proper etching process is an effective route to reducing the SSBs in 4H-SiC homoepitaxial layers.

Three-phase (solid, melt, and gas) and two-phase (solid and melt) models of horizontal ribbon growth were compared to identify the significance of different gas effects. The boundary conditions at the melt–gas and solid–gas interfaces for two-phase simulations were obtained from decoupled simulations of the gas phase. The results showed that the gas shear stress strongly changes the flow and temperature fields and the position of the triple-phase line. Also, the gas pressure distribution determined the vertical position of the triple-phase line. In the absence of growth angle effects, the results of the two-phase model with specified convective heat transfer coefficient, shear stress, and pressure as boundary conditions along the gas phase interface closely matched that of the three-phase model. Even with non-zero growth angle effects, the two-phase model with all the boundary conditions agreed well with three-phase simulation results, despite increased deviations at higher pull speeds. Finally, the results indicated that gas-induced velocities are significant compared to the Marangoni and buoyancy velocities, which could lead to flow instabilities and the variations in solid shape as observed in HRG experiments.

Yttrium calcium oxyborate (YCOB) crystals are excellent nonlinear optical crystals. To enhance the thermal properties of YCOB crystal, Sc-doped YCOB crystals, denoted as Sc_xY_1-xCa₄O(BO₃)₃ (x = 0.1 and 0.2) were grown using the Czochralski method along the b-direction. Various measurements, including X-ray powder diffraction, rocking curve analysis, inductively coupled plasma-optical emission spectroscopy (ICP-OES), transmission spectroscopy, density measurements, and thermal property assessments, were conducted to evaluate the characteristics of the Sc_xY_1-xCOB crystals. The results indicated that Sc_xY_1-xCOB crystals have an isostructural arrangement like YCOB, with segregation coefficients of approximately 0.2. The full width at half maximum (FWHM) values of the rocking curves of the Sc_xY_1-xCOB (x = 0.1 and 0.2) crystals are 33.9″ and 29.3″, respectively. Furthermore, the specific heat, thermal diffusion coefficients and thermal conductivity of the Sc_xY_1-xCOB crystals were examined in the temperature range of 298–573 K, which were found to be higher than those of pure YCOB. These high-quality Sc_xY_1-xCOB crystals are expected to serve as suitable nonlinear optical crystals media for optical parametric chirped pulse amplification (OPCPA) applications.

High-quality single crystals of both pure and Sn:β-Ga₂O₃ single crystals were grown using the optical floating zone technique and a comprehensive study of its luminescence and scintillation properties was carried out. The pure and Sn:β-Ga₂O₃ grown crystals were oriented along (1 0 0) by Laue diffraction pattern and its monoclinic structure was confirmed using a single crystal XRD. X-ray induced luminescence spectrum shows a maximum emission peak at 365 nm. The cut off wavelength was observed around 258 nm and the optical band gap was calculated to be 4.64 eV from UV–Vis-NIR transmission spectroscopy. The room temperature Raman spectra were recorded and the various vibration modes were investigated. Low temperature (10 to 300 K) and high temperature (325 to 675 K) TL measurements were carried out on X-ray irradiated crystals and its TL kinetic parameters such as activation energy (eV) and frequency factor (S) were calculated. Scintillation decay time profiles were measured for both pure and Sn-doped crystals under ¹³⁷Cs γ-ray excitation. The calculated scintillation light output is 2300 Ph/5.5 Mev for Sn:β-Ga₂O₃ crystal under α-particle excitation from ²⁴¹Am radiation source.

In this study, N-Structured based InAs/AlSb/GaSb Type-II Superlattice pbin type detector structures are investigated. These systems make absorption in the infrared region in the electromagnetic spectrum as detectors. Structural characterization of these systems is aimed. n-type GaSb is used as the substrate. InAs/AlSb/GaSb-based repetitive SL layers are formed as n-layer, i-layer, p-layer, and p-contact layer from the bottom InAsSb layer to the top GaSb cap layer for 120, 300, 15, and 80 periods, respectively. Structural characterization of all layers is made by using SIMS and XRD systems analyses. The structural depth profile of the SL layers has been presented comparatively through SIMS analysis. The interfacial transitions observed in the depth profile are consistent with the designed T2SL layers. By using XRD characterization, crystal quality parameters, lattice constants, periodicity, and deviation of superlattice peak from the substrate are determined. Such dislocation density and strain are measured AS 7.85x10⁷cm⁻² and 6.4x10^-3 nm, respectively. AFM analysis technic is used to examine the surface morphology of the structure. Also, SEM analysis is used to examine the cross-section of the structure. The cross-sectional measurements allowed the observation of interfacial transitions within the SL structure. In this study, super lattice with high crystal quality is achieved and results show that T2SL detector structures have succeeded.

To investigate the effect of high-power laser heating on the floating zone (FZ) method, a crystal of β-Ga₂O₃ was grown by the LDFZ method using a newly developed optical system equipped with a 20-kW laser diode (LD) system as a heat source. The growth started from a twin-free seed crystal with a diameter of 7 mm and the diameter of the crystal was increased gradually up to 30 mm. With increasing the diameter of the crystal, three patterns of the beam intensity profile were switched to heat the whole of the molten zone locally and intensively. The intensity profile of the five beamlets irradiating the sample was adjusted with a combination of the zooming by the optical system and the partial blocking by the alumina cylinder. By the proper tuning of the beam profile and the proper selection of the diameter of the feed rod, the molten zone was kept stable against gravity. The obtained crystal has a layer texture without clear facets or cracks. It almost conserves the crystallographic direction of the seed crystal but is twinned except for a twin-free region near the seed crystal.

Lead zirconate titanate (PZT) of composition Pb(Zr_XTi_1−X)O₃ is a non-congruently melting material, so crystal growth must be done from a high temperature solution. An understanding of the high temperature solution phase diagram is necessary to make this possible. A variety of solvent systems and solvent properties were evaluated for the growth of PZT, and two innovative lead oxide-phosphate solvents were developed: PbO-PbLiPO₄ (PLP), and PbO-Pb₂P₂O₇ (lead pyrophosphate). PZT crystals were grown from these solvents with compositions near the desirable morphotropic phase boundary composition X = 0.52. Both PLP and Pb₂P₂O₇ form molecular complexes in the melt that participate minimally in the solution of PZT, which is dissolved by the free uncomplexed PbO acting as both a solvent and solute ingredient. The phosphates do favorably reduce the melting temperature, PbO evaporation, density, and position of the melting minimum. These solvents were used to determine liquidus and solidus curves over the range of interest in X, and to develop a universal solubility equation. Modeling was used to fit and extrapolate these PZT-solvent phase diagrams to other PbO-based solvents. These results explain prior art data and point to a congruently melting indifferent point at the lead titanate end of the phase diagram.

CdZnTe (CZT) is the preferred material for HgCdTe (MCT) infrared detectors and room temperature nuclear-radiation detector applications. However, their widespread application is hindered by the low yield, attributed to intrinsic thermophysical properties like extremely low thermal conductivity and stacking fault energy, complicating the growth of large-volume crystals. Based on steady-state computer numerical modeling simulation, this paper examines the impact of seed size variations (from 15 mm to 90 mm) in the crystal growth process on the initial growth surface morphology, simulations indicate that larger seed crystals are predisposed to developing more convex interfaces, which are conducive to enhanced crystal growth. An optimized Vertical Gradient Freeze (VGF) method employing iso-diameter seed (having the same diameter as the grown crystals) of approximately 90 mm has been developed to grow single crystals with reduced defect density in a VGF furnace, and the applications in liquid phase epitaxy (LPE) are also discussed.

High-quality Na₂Gd₂(BO₃)₂O crystals have been successfully grown using the top-seeded solution growth method (TSSG), employing a Na₂O - NaF - B₂O₃ flux system with optimal molar ratios of Na₂Gd₂(BO₃)₂O : Na₂CO₃ : NaF : H₃BO₃ = 1:2:6:4. The magnetic and magnetocaloric properties were investigated including magnetic susceptibility (χ), magnetization (M), and isothermal magnetic entropy change (−ΔS_m) measurements. Na₂Gd₂(BO₃)₂O exhibits a large magnetocaloric effect with a maximum − ΔS_m of 41.6 J·kg⁻¹·K⁻¹ at 2 K and 7 T, which is higher than that of commercial Gd₃Ga₅O₁₂ (GGG, −ΔS_m = 38.4 J·kg⁻¹·K⁻¹ at 2 K and 7 T) and most other Gd³⁺-based borates, showing the potential application in the field of magnetic refrigeration.

Ni, Sn co-doped ZnO nanoparticles have been prepared by chemical method at room temperature. The effects of Sn on the structural, morphological, optical, electrical, and anti-microbial properties of the prepared nanoparticles have been evaluated and discussed. The crystallite size and the unit cell properties have been influenced by the doping concentration of Sn. The addition of Sn enhances the texture coefficient of the nanoparticles. The optical band gap of the material is blue-shifted as the doping concentration of Sn increases. The prepared nanoparticles have high hole concentration than electron concentration. The nanoparticles became more transparent at high doping concentrations. The effect of Sn concentration against E. coli, S. aureus, and P. aeruginosa has been evaluated.