Bridgman-grown Crystals Research Articles

Structural and angle-resolved optical and vibrational properties of chiral trivial insulator InSeI

Chiral materials, known for their unique structural and quantum properties, have garnered significant interest, with InSeI emerging as a promising chiral topologically trivial insulator. In this study, we introduce a scalable Bridgman crystal growth technique to synthesize large, environmentally stable single crystals of InSeI, achieving centimeter-sized chiral crystals with superior quality. Notably, this work marks the first report of photoluminescence (PL) emission from exfoliated InSeI chiral chains, alongside a detailed exploration of their polarization-dependent optical and phononic properties. Our Bridgman-grown crystals exhibit excellent structural integrity, enhanced exfoliation characteristics, and increased resistance to light-induced degradation compared to those produced by traditional solid-state methods. A microscopy analysis confirms the distinct chiral structure of InSeI, and the first in situ nanometer spatial resolution electron energy loss spectroscopy measurements establish a bandgap of 2.08 eV, consistent with the cryogenic PL emission peak. Angle-resolved Raman spectroscopy, combined with calculated vibrational properties, identifies five distinct frequency regions in the Raman modes, predominantly associated with In-, In-I, In-Se-I, and Se-atomic motions, with significant intensity variations under different polarization orientations. This study not only offers a practical method for synthesizing high-quality InSeI but also provides the first comprehensive experimental insights into its unique optical and vibrational properties, significantly advancing the understanding of chiral material systems.

Interconfigurational d-f luminescence of Pr3+ ions in praseodymium doped Li6Y(BO3)3 single crystals

Luminescence properties of undoped Li6Y(BO3)3 (LYB) crystals grown by the Bridgman method as well as undoped and praseodymium doped LYB crystals grown by the Czochralski method were studied under excitation by ultraviolet light, synchrotron radiation and electron beam in the temperature region of 5–300 K. The emission bands peaking at 4.8, 3.76 and 2.95 eV were found in undoped Czochralski-grown crystals, while the band at 3.34 eV was dominant in the Bridgman-grown crystals. These bands are presumably ascribed to excitons localized at regular and defect-perturbed lattice sites. Intense emission bands peaking at 4.75, 4.50, 4.17 and 3.98 eV were discovered in Pr doped crystals at low temperatures and related to the interconfigurational 4f15d1 → 4f2 radiative transitions in Pr3+ ions. The structure of the emission spectrum is shown to be determined by the 3H4, 3H5, 3H6, 3F2, 3F3, 3F4 terms of the Pr3+ ion. The characteristic decay time of the 4f15d1 → 4f2 emission is τ = 24 ns at low temperatures, however, it shortens to 9 ns by room temperature due to a strong thermal quenching. The study of glow curves and spectra of thermostimulated luminescence in Li6Y(BO3)3:Pr crystal irradiated by 10-keV electron beam shows that Pr3+ ions do not participate in an electron-hole recombination process.

The visibility and stability of GaSe nanoflakes of about 50 layers on SiO2/Si wafers

GaSe nanoflakes on silicon substrates covered by SiO2 films are prepared by mechanical exfoliation from the bulk Bridgman-grown GaSe crystals using a scotch tape. The thickness of SiO2 films on Si substrates providing the highest optical contrast for observation of GaSe flakes is estimated by taking into account the spectral sensitivity of a commercial CMOS camera and broadband visible light illumination. According to our estimations, the optimal SiO2 thickness is [Formula: see text]126 nm for the visualization of GaSe flakes of 1–3 layers and [Formula: see text]100 nm for the flakes of 40–70 layers. The obtained nanoflakes are investigated by optical and atomic force microscopy and Raman spectroscopy. The observed spectral positions of the Raman peaks are in agreement with the positions of the peaks known for bulk and nanolayered GaSe samples. It is found that the 50 nm thick flakes are stable but are covered by oxide structures with lateral size about 100 nm and height [Formula: see text]5 nm after [Formula: see text]9 months exposure to ambient atmosphere.

X‐Ray Topography: X‐Ray Topography Characterization of the Bridgman‐Grown Crystals of Zinc Germanium Phosphide (Crystal Research and Technology 11/2018)

Crystal Research and TechnologyVolume 53, Issue 11 1870020 Cover PictureFree Access X-Ray Topography: X-Ray Topography Characterization of the Bridgman-Grown Crystals of Zinc Germanium Phosphide (Crystal Research and Technology 11/2018) First published: 08 November 2018 https://doi.org/10.1002/crat.201870020AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Graphical Abstract X-ray image of the zinc germanium phosphide crystal obtained at the synchrotron radiation using the rocking topography technique. More details can be found in article number 1800154 by Alexander A. Kaloyan, Konstantin M. Podurets, and co-workers. Volume53, Issue11November 20181870020 RelatedInformation

Enhancement of thermoelectric figure of merit in β -Zn4Sb3 by indium doping control

We demonstrate the control of phase composition in Bridgman-grown β-Zn4Sb3 crystals by indium doping, an effective way to overcome the difficulty of growing very pure β-Zn4Sb3 thermoelectric material. The crystal structures are characterized by Rietveld refinement with synchrotron X-ray diffraction data. The results show an anisotropic lattice expansion in In-doped β-Zn4Sb3 wherein the zinc atoms are partially substituted by indium ones at 36f site of R-3c symmetry. Through the elimination of ZnSb phase, all the three individual thermoelectric properties are simultaneously improved, i.e., increasing electrical conductivity and Seebeck coefficient while reducing thermal conductivity. Under an optimal In concentration (x = 0.05), pure phase β-Zn4Sb3 crystal can be obtained, which possesses a high figure of merit (ZT) of 1.4 at 700 K.

Comparative Study of Shallow Acceptor Levels in Unintentionally Doped p-Type GaSe Crystals Prepared by the Bridgman and Liquid Phase Solution Growth Methods

GaSe crystals were grown by liquid phase solution growth, using the temperature difference method under controlled vapor pressure. Temperature-dependent Hall effect measurements were used to show the different thermal activation energies of the acceptor levels of the commercially available Bridgman-grown GaSe crystals and our liquid phase solution-grown crystals. Unintentionally doped GaSe crystals showed p-type conduction; also, the thermal activation energies of the acceptor levels of the Bridgman-grown crystals were 30 meV + Ev and 50 meV + Ev while that of liquid phase-grown crystals was 15 meV + Ev (where Ev is the energy of the valence band). We conclude that low temperature growth and stoichiometry control can effectively inhibit native point defect formation.

Growth and uniformity improvement of large-size PbWO4 crystal with PbF2 doping

PbF2-doped lead tungstate (PbWO4) scintillation crystals have been grown by the modified vertical Bridgman method along 〈001〉 orientation. Large-size PbWO4 crystals up to 200mm in length and 24×24mm2 in section have been obtained reproducibly. The uniformity of the crystal block has been investigated by means of X-ray diffraction (XRD), longitudinal transmittance, X-ray excited luminescence and light yield. The results showed that Bridgman-grown PbWO4 crystals have good optical and scintillation uniformity.

Liquid-phase epitaxy of GaSe and potential application for wide frequency-tunable coherent terahertz-wave generation

GaSe is one of the most promising semiconductor crystals for wide frequency-tunable terahertz (THz) wave generation by photo mixing. The ε-type monocrystalline GaSe crystals were successfully grown by the liquid-phase epitaxy at constant and low (530–590 °C) growth temperatures under the controlled different selenium (Se) vapor pressures ( P Se ∼0–7.75 Torr). From the coherent THz-wave spectroscopy, the absorption spectra have shown different resonant frequencies and absorption coefficients due to the stoichiometry-dependent point defects which depend on the applied P Se . It is shown that the resonance in GaSe under P Se ∼0 Torr shifts towards the lower THz frequencies compared with those under high P Se , maybe due to the degraded intermolecular interactions caused by the introduction of Se vacancy-related defects. The absorption coefficients (1–5 THz) decreased according to the increase of Se vapor pressure, thus the transparency of GaSe under higher P Se is improved by an amount of 25% compared with that of Bridgman-grown crystals. By using Bridgman-grown GaSe crystals, coherent-THz wave was generated by the difference frequency method (DFM) in a wide frequency range of 0.1–70 THz. Coherent-THz spectroscopy is a revolutionary method for the evaluation of molecular structures and defects in organic molecule also could be analyzed.

Growth of Rare-Earth-Doped K2LaCl5, K2BaCl4, and K2SrCl4 Single Crystals

Processes are described for the synthesis and melt growth of rare-earth-doped K2LaCl5, K2BaCl4, and K2SrCl4, using rare-earth oxides as starting materials. The solubility of rare-earth activators in Bridgman-grown crystals are determined, and the spectroscopic properties of K2LaCl5〈Nd〉 crystals are investigated.

Thermal expansion and thermal conductivity of CuGa1−x InxTe2 solid solutions

The thermal expansion coefficients and the thermal conductivity of Bridgman-grown crystals of CuGa1−x InxTe2 solid solutions are investigated. It is found that the thermal expansion coefficient varies with x linearly, while the thermal conductivity is minimal when x=0.5. The Debye temperature and the rms dynamic atomic displacements are calculated from experimental data. It is shown that the Debye temperature decreases and the rms displacements in the crystal lattice sharply increase as the In content in the solid solutions grows.

Vacuum evaporated CsPbX 3 ( X=Cl, Br, I) thin films: optical and transport properties

Thin films of ternary CsPbX 3 compounds were prepared by vacuum co-evaporation of CsX and PbX 2 purified powders. Bridgman-grown crystals of the ternary CsPbX 3 phases were also evaporated to produce “bulk-like” (BE) thin films. The films are constituted by nanocrystallites as evidenced by X-ray diffraction (XRD) and Atomic Force Microscopy (AFM). Electrical characterization reveals a complex response of the materials either on the applied voltage or temperature variations. I( V) curves are ohmic for low voltages while an exponential increase is observed over 80 V, which supports a field-assisted emission contribution to the dark current. Degenerate scattering mechanisms control the carriers transport at the lower temperatures while activate conduction with energy barrier lower than one half the band gap takes place for temperatures greater than 300 K in all deposited materials. A model is proposed to discuss the experimental results.

CZT detectors fabricated from horizontal and vertical Bridgman-grown crystals

Characterizations of Cd 1− x Zn x Te (0.04< x<0.24) detector crystals grown by vertical high-pressure Bridgman (VHPB), vertical ambient pressure Bridgman (VB), horizontal ambient pressure Bridgman (HB) and vapor-grown crystals obtained from various sources were compared. The following methods were applied: (1) Triaxial double crystal X-ray diffraction (TADXRD) to determine the crystal homogeneity and Zn content. (2) Sensitivity to radiation from high-flux X-rays to investigate detector efficiency and contacts. (3) Laser-induced transient charge technique (TCT) for measuring the carrier lifetimes. (4) Thermoelectric voltage spectroscopy (TEVS) and thermal-stimulated current spectroscopy, (TSC) to study the carrier traps. (5) IR imaging to characterize macroscopic crystalline defects. We compared cadmium zinc telluride crystals grown by different methods in order to understand better the nature of defects, which influence their nuclear spectroscopic response, and how the defects are affected by the growth technique.

Phase transitions in the (Cs1−x Rbx)2ZnI4 system

(Cs1−xRbx)2ZnI4 crystals were grown by two different methods with Rb concentrations varying from x=0 to 2.5%. 127I NQR and calorimetric measurements showed that crystals grown by the Bridgman technique contain residual impurities (∼0.5%) for all x. While x=0 crystals grown from solution do not contain detectable impurities, they allow incorporation only of a low Rb concentration, not above 0.5%. A transition-temperature-concentration (x) phase diagram has been constructed for Bridgman-grown crystals from NQR data. Rb doping shifts the normal-incommensurate and incommensurate-ferroelastic phase-transition points toward higher temperatures with different rates. The P21/m↔P1 first-order transition shifts toward lower temperatures. The region of low Rb concentrations lies closest to the critical point.

Cleavage Planes in CuInSe2

All angles between facets in CuInSe 2 Bridgman-grown crystals were measured and confirmed, by X-ray Laue patterns and diffractometry, to be accounted for by three planes: {101}, {112} and {110}. The {110} facets were less frequent and were found to consist of {112} microcleavages. The {101} cleavages occurred most frequently and it is speculated that this is due to the smaller energy required to break a smaller number of the stronger Se–Cu bonds (compared with the weaker Se–In bonds) than for {112} cleavages.

Low temperature ESR spectra of nickel — doped NaCl crystals

Paramagnetic resonance of Bridgman-grown NaCl crystals nominally doped with divalent nickel was studied over the temperature range from 4 K to 300 K. The broad isotropic EPR line with g = 2.12 ÷ 2.23 and ΔHpp = 280 ÷ 780 G was detected at temperatures higher than 130 K for samples of various thermal history. The origin of these spectra was attributed to aggregated and precipitated Ni2+ ions. At temperatures lower than 40 K another ESR signal was registered. It was an anisotropic one, the intensity of which strongly depends upon the temperature. This spectrum results from substitutional Ni+ ions with tetragonally distorted surrounding along a S100T direction. The angular dependence of the ESR line positions was fitted to an appropriate spin-Hamiltonian with the g-factor components g∥ and g⊥ equal to 2.86 and 2.10, respectively. The temperature-dependence of the signal intensity at temperatures between 4 and 110 K has been interpreted in terms of a transition from the static to dynamic Jahn-Teller effect.

Study of zinc inclusions/precipitates in CdZnTe crystals

Zn inclusions/precipitates in Bridgman-grown CdZnTe crystals, for the first time, have been characterized by scanning electron microscopy with an electron probe X-ray microanalyzer (SEM/EPMA). The Zn inclusions/precipitates in CdZnTe crystals are possibly due to Zn segregation effects resulting from the deviation from the congruent melting point. It is also shown that Te- and Cd-rich regions surrounding the Zn inclusions/precipitates edge, due to the non-stoichiometric solid compositions, lead to the formation of Te and/or Cd precipitates around the Zn inclusions/precipitates. The infrared transmittance of these stoichiometric-type CdZnTe is about 64% in the wavenumber range of 400–4000 cm −1.

Identification of oxygen in the copper as the source of adhesion in Bridgman-grown CuInSe2 crystals

In synthesizing CuInSe2 from its starting elements for subsequent Bridgman crystal growth, a closed ampoule is used to prevent the loss of selenium. Frequently, the resulting ingot adheres strongly to the inner wall of the ampoule, unless a getter is included, such as graphite or boron nitride. The present work, shows that the “ingot sticking” problem is due to oxygen in the starting copper, even though this element is nominally of five-nines purity. Ingots of CuInSe2 prepared with oxygen-free copper, pumped-on-heated copper, or copper heated separately with boron nitride all show a reduction in adherence to the ampoule wall or exhibit no sticking at all. Gas analysis during the heat treatment has confirmed the presence of oxygen in the five-nines-pure copper and its reduction with continued pumping and heating.

An electron paramagnetic resonance and magneto-optical study of vanadium in

The vanadium-related defects in high-resistivity Bridgman-grown (x = 0.04, 0.10) crystals have been studied by electron paramagnetic resonance (EPR) and magnetic circular dichroism absorption spectroscopy (MCDA). Only one vanadium-related spectrum is observed by EPR, which is attributed to a defect in orthorhombic point symmetry. Its spin Hamiltonian parameters are electron spin S = 3/2, Landé g-tensor , , , crystal field splitting parameters and , nuclear spin I = 7/2, hyperfine tensor , , with the principal axes x, y, z oriented along the [110] , [001], [-110] directions respectively. The MCDA measurements performed on the same crystals show in addition to the absorption bands of the ion those of the ion, a defect not observed by EPR; the non-observation of the EPR spectrum is ascribed to a strong zero-field splitting of the groundstate. The low point symmetry of the defect is attributed to the formation of second nearest neighbour complexes in the Zn-alloyed CdTe samples.

Gamma-ray detectors from thermally annealed Bridgman-grown CdTe

The characteristics of small γ-ray probe detectors (hemispherical contact geometry) made from Cl- and In-doped Bridgman-grown crystals of CdTe are described. A slow, low-temperature anneal of as-grown CdTe ranging from 485 to 85°C, and cooled at a rate of < 20°C/h, was found to greatly improve detector performance. Best photopeak to Compton edge ratios were 2:1 for 662 keV γ-rays. Typical values were 1:1 with energy resolutions of 5% full width at half maximum. Energy resolution was ∼ 13.5% for 185 keV γ-rays from a 235U (93%) source.

Effect of vibrational stirring on the quality of Bridgman-grown CdTe

The coupled vibrational stirring (CVS) method was applied to the vertical Bridgman growth of CdTe. This new stirring method involves orthogonally coupling a set of low frequency transverse vibrations to a growth ampoule. The motion imparted to the ampoule gives rise to rapid, controlled spiral flows. Dopant distributions in CVS grown, phosphorous-doped CdTe boules were studied by measuring free carrier concentrations. CVS improved the chemical homogeneity of Bridgman-grown crystals. From the isoconcentration curves, the growth interface was observed to be much flatter than in boules grown without CVS, which is desirable to minimize radial strain. Some degradation in microstructure was detected from the CVS processing conditions used in these experiments. This effect needs to be studied further.