X-ray characterization of detached-grown germanium crystals

Germanium (1 1 1)-oriented crystals have been grown by the vertical Bridgman technique, in both detached and attached configurations. Microstructural characterization of these crystals has been performed using synchrotron white beam X-ray topography (SWBXT) and double axis X-ray diffraction. Dislocation densities were measured from X-ray topographs obtained using the reflection geometry. For detached-grown crystals, the dislocation density is on the order of 10⁴ cm⁻² in the seed region, and decreases in the direction of growth to less than 10³ cm⁻², and in some crystals reaches less than 10² cm⁻². For crystals grown in the attached configuration, dislocation densities were on the order of 10⁴ cm⁻² in the middle of the crystals, increasing to greater than 10⁵ cm⁻² near the edge. The measured dislocation densities are in excellent agreement with etch pit density (EPD) results. Broadening and splitting of the rocking curve linewidths was observed in the vicinity of subgrain boundaries identified by X-ray topography in some of the attached-grown crystal wafers. The spatial distribution of rocking curve linewidths across the wafers corresponds to the spatial distribution of defect densities measured in the X-ray topographs and EPD micrographs.     

Investigation of semi-insulating oxygen-doped GaAs

We found Oxygen-doped GaAs crystals to be suitable materials for CO₂ laser optical component preparation, with application at 10.6 μm. An optical transmission of 55% in the IR spectrum range, between 2 and 15 μm has been reached for such a GaAs type material. The GaAs crystals that we have analysed were grown by two procedures: Horizontal Bridgman (HB) and Liquid Encapsulated Czochralski (LEC). The HB method has been used for obtaining pure (undoped) crystals, while the oxygen-doped GaAs ingots were grown by LEC technique. The two types of samples processed in the same manner as regards mechanical polishing and chemical etching, which were investigated by Hall measurements, optical transmission spectrometry and elastic recoil detection analysis (ERDA) technique. The GaAs:O (LEC) has near semi-insulating properties as can be observed from the results of the electrical resistivity and Hall effect measurements. The ERDA spectrum shows an intense signal of oxygen in the bulk of GaAs:O (LEC) crystals, while the oxygen signal is not present in the ERDA spectrum of the undoped GaAs (HB). We consider that these results could recommend the ERDA technique as a possible qualitative and quantitative analysis in an ion-beam accelerator for oxygen content in oxygen-doped GaAs crystals. The analysis is not sensitive to the native oxide, as could be seen by measuring GaAs (HB) undoped crystals.     

Phase diagram of the SrS–Ga2S3 system and its application to the single-crystal growth of SrGa2S4

Ce-doped SrGa₂S₄ compound is expected as a new host material of blue EL devices. However, the basic properties of bulk single crystals have not been fully clarified, since this compound has been mostly synthesized in the form of polycrystals or thin films. Here, we firstly present the pseudo-binary phase diagram of the SrS–Ga₂S₃ system constructed in accordance with our DTA data for single-crystal growth of SrGa₂S₄. It is shown that SrGa₂S₄ compound has a congruent melting point and a eutectic reaction in the side of excess of Ga₂S₃ concentration. On the basis of the phase diagram, single crystals of SrGa₂S₄ are grown using Ga₂S₃ as a self-flux in a horizontal Bridgman furnace. Colorless and transparent crystals having a typical size 2×2×2 mm³ are obtained.     

Growth and properties of Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 single crystals directly from melt

Pb[(Zn_1/3Nb_2/3)_0.91Ti_0.09]O₃ (PZNT91/9) single crystals were grown by a modified Bridgman method directly from melt using an allomeric Pb[(Mg_1/3Nb_2/3)_0.69Ti_0.31]O₃ (PMNT69/31) single crystal as a seed. X-ray diffraction (XRD) measurement confirmed that the as-grown PZNT91/9 single crystals are of pure perovskite structure. Electrical properties and thermal stabilization of PZNT91/9 crystals grown directly from melt exhibit different characters from those of PZNT91/9 crystals grown from flux, although segregation and the variation of chemical composition are not seriously confirmed by X-ray fluorescence analysis (XPS). The [0 0 1]-oriented PZNT91/9 crystals cut from the middle part of the as-grown crystal boules exhibit broad dielectric-response peaks at around 105 °C, accompanied by apparent frequency dispersion. The values of piezoelectric constant d₃₃, remnant polarization P_r, and induced strain are about 1800–2200 pC/N, 38.8 μC/cm², and 0.3%, respectively, indicating that the quality of PZNT crystals grown directly from melt can be comparable to those of PZNT91/9 single crystals grown from flux. However, further work deserves attention to improve the dielectric properties of PZNT crystals grown directly from melt. Such unusual characterizations of dielectric properties of PZNT crystals grown directly from melt are considered as correlating with defects, microinhomogeneities, and polar regions.     

Bridgman growth and properties of potassium lithium niobate single crystals

Transparent KLN crystals 10mm in diameter and 25 to 45mm in length have been grown by the modified vertical Bridgman technique from different melts in the range of 3035mol% K₂O, 1723mol% Li₂O and 4350mol% Nb₂O₅. The growth conditions are a growth rate of less than 0.25 mm/hr, temperature gradient in solid-liquid interface of 23 °C/mm and growth direction of <110>. As-grown KLN crystals have tetragonal tungsten bronze structure. Most of the as-grown crystals do not crack when cooling through the paraelectric/ferroelectric phase transition. 180° domain structures are observed after the KLN crystal was etched in boiling 2HNO₃:Hf. Dielectric properties and transmission spectrum of the as-grown KLN crystals are measured.     

Crystal growth of Ce: PrF3 by micro-pulling-down method

Micro-pulling-down (μ-PD) growth apparatus was modified for fluoride crystals. PrF₃ was grown with various concentrations of Ce³⁺ from 0–100%. The crystals were transparent and colorless (CeF₃) or greenish and 3 mm in diameter and 15–50 mm in length. Neither visible inclusions nor cracks were observed. Radioluminescence spectra and decay kinetics were measured for the sample set at room temperature. In comparison to the Czochralski or Bridgman method, the μ-PD method allows to produce single crystalline material in a faster thus more economic way. Once it is established for the fluoride crystals, it is an efficient tool for exploring the field of new functional fluorides.     

Compensation Mechanism in Vanadium and Gallium Doped CdTe and (Cd,Zn)Te

Vanadium and gallium doped CdTe crystals were grown from the vapour phase (modified Markov method) and (Cd_0.9Zn_0.1)Te: V from the melt (vertical Bridgman). The crystals were characterized by photoinduced current transient spectroscopy (PICTS), photoluminescence (PL) and time dependent charge measurements (TDCM). Transitions from different charge states (V²⁺/V³⁺) of the vanadium donor have been observed in the V-doped crystals by PICTS. A shallow donor level (dE = 0.068 eV) and the Ga A-center have been identified by PICTS and PL measurements in CdTe:Ga. In case of V-doping high resistivity is achieved all over the crystal while Ga-doping results in a high resistivity region only in the middle of the crystal. Calculation of the resistivity by means of a compensation model shows that for both dopants an additional not observed deep donor has to be assumed in order to describe the resistivity distributions.     

Large-size β-Ga2O3 single crystals and wafers

Large-size single crystals of β-Ga₂O₃ with 1 inc in diameter have been grown by the floating zone technique. The stable growth conditions have been determined by the examination of the crystal structure. Wafers have been cut and fine polished in the (1 0 0), (0 1 0) and (0 0 1) planes. These were highly transparent in the visible and near UV, as well as electrically conductive, indicating the potential use of β-Ga₂O₃ as a substrate for optoelectic devices operating in the visible/near UV and with vertical current flow.     

Growth and luminescence mechanisms of Ba2ErCl7: a new laser up-conversion crystal

A modified synthesis method for the preparation of Ba₂ErCl₇, a new laser up-conversion material using Er₂O₃, BaCl₂·2H₂O and NH₄Cl, is reported for the first time. Single crystals 5–8 mm in diameter and 10–20 mm in length were grown by both the Czochralski and Bridgman methods. The transmittance spectra for a Ba₂ErCl₇ single crystal was first measured using a HITACHI U-3500 spectrophotometer. There were three intense absorption peaks ⁴I_9/2, ⁴I_11/2 and ⁴I_13/2 in the infrared range which can be excited by 803 and 980 nm and 1.5 μm laser diode (LD), respectively. The cut-off wavelength of the crystal was 230 nm. Intense green luminescence was observed when the crystals were pumped by an 803 nm LD. Up-conversion mechanisms are discussed.     

Dislocations in CdTe

Two different etchants were developed to get boat- and triangular type etch pits on CdTe crystals. The subboundaries are shown to be symmetrical tilt boundaries. Dislocation density and microhardness measurements were made on three CdTe crystals grown by Bridgman, Travelling heater and vapour phase technique and were correlated.     

氧气对CsPbBr3单晶电学性能的影响

CsPbBr₃兼具高探测效率和较好的稳定性,是当前高性能高能辐射探测器的热门材料。在使用坩埚下降法制备CsPbBr₃单晶的配料阶段,如果无法有效隔绝原料与氧气的接触,氧气会吸附于原料表面难以排出,在原料熔化后会聚集在密封坩埚的上方,导致所得到的单晶颜色沿生长方向逐渐变深,这一颜色变化不会改变CsPbBr₃的禁带宽度。通过对单晶上端切片进行电学性能测试发现,从单晶的中心到外侧,CsPbBr₃单晶的电阻率逐渐下降,陷阱密度和载流子迁移率逐渐增大,但对X射线的响应度基本不变。本文为研究高质量CsPbBr₃单晶的生长提供帮助。     

Defect characterization and composition distributions of mercury indium telluride single crystals

A mercury indium telluride (MIT) ingot was grown by the vertical Bridgman method. The defects in MIT crystals were characterized by the chemical etching method. A defect etchant for MIT crystals was developed. The etch pits of dislocations, microcracks and boundary was observed by scanning electron microscopy. It was elucidated that the etch pits density of dislocations of MIT wafers was about 4×10⁵ cm⁻². Te and In reduced at the grain boundaries, but were homogeneously distributed within the grains in the as-grown MIT crystals. The distribution of In in MIT crystals along the growth direction and radial direction was analyzed by electronic probe microscopy. It was found that In concentration was higher in the initial part and lower in the final part of the MIT ingot, which indicated that the segregation coefficient of In in MIT crystals was 1.15. The radial In concentration increased from the center to edge of the wafers and homogeneous in the middle part.     

Porous crystal structures obtained from directionally solidified eutectic precursors

Interconnecting cage-like porous structures of several halide compounds were prepared by the selective leaching of one eutectic phase method. The binary eutectic precursors were prepared by directional solidification using the Bridgman crystal growth technique. Porous NaMgF₃ (40% pore volume), CaF₂ (57% pore volume) and BaF₂ (43% pore volume) crystals were obtained after water leaching the NaF component of the directionally solidified NaF/NaMgF₃, NaF/CaF₂ and NaF/BaF₂ eutectics with the appropriate entangled microstructure. The growth conditions for eutectic-coupled growth and the morphology of the eutectics have been determined. In the coupled growth regime, the size of the eutectic phases “λ” is fairly uniform and varies with the eutectic growth rate “v” as λ²v=constant, which allows us to control the pore size within the 0.5–10 μm range. The simplicity and versatility of the eutectic growth also allows us to fabricate highly aligned porous structures at relatively high production rates.     

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.     

Growth, morphological and structural characterization of Pb1−xSnxTe single crystals

Pb_1−xSn_xTe single crystals have been grown by a vertical Bridgman method. They have typical Hall mobilities and carrier concentration values of 10³ cm²/V · s and 10¹⁸ cm^-3, respectively, and change from p- to n-type as the Sn content increases. The ingots were single crystal with a subgrain structure that has a misorientation no higher than 2′. The segregation of Sn has been determined and it suggests that there is a convective flow in the liquid.     

Influence of growth conditions on microstructure and properties of GaSe crystals

GaSe crystals have been grown from melt. There are several reasons why it is difficult to meet ideal demands for nonlinear optic material, GaSe single crystal. First, these crystals have a tendency towards lamination because of great difference in a and c crystal lattice parameters and very weak Vander der Waals forces in c direction. Next, there is a great difference in saturation vapor pressure of the components, which can cause nonstoichiometry of a melt-grown crystal composition. Another obstacle in the growth of perfect GaSe crystals is dendrite formation caused by instability of the growth front. To overcome this obstacle we used Bridgman technique and have found the temperature and pressure conditions, and growth velocity which provide growth of perfect bulk single crystals of about 100 mm in length and 20 mm in diameter. Sharp Laue patterns and a rocking curve confirm perfect structure of the grown crystals. Electron-probe X-ray microanalysis shows stoichiometric composition of GaSe crystals and X-ray phase analysis reveals presence of single-phased hexagonal structure.     

Growth and characterization of CdSe single crystals by modified vertical vapor phase method

Good quality, large single crystals of CdSe were grown by the modified growth method (i.e., vertical unseeded vapor phase growth with multi-step purification of the starting material in the same quartz ampoule without any manual transfer between the steps). Lower temperature gradients (8–9°C/cm) at the growth interface were used for the crystal growth. As-grown CdSe crystals was characterized by X-ray diffraction, scanning electron microscopy, energy dispersive analyzer of X-rays, high-resistance instrument measurement, and etch-pit observation. It is found that there are two cleavage faces of (1 0 0) and (1 1 0) orientations on the crystal, the resistivity is about 10⁸ Ω cm, and the density of etch pits is about 10^3–4/cm². The crystal was cut into wafers and was fabricated into detectors. The detectors were tested using an ²⁴¹Am radiation source. γ-ray spectra at 59.5 keV were obtained. The results demonstrated that the quality of the as-grown crystals was good. The crystals were useful for fabrication of room-temperature-operating nuclear radiation detectors. Therefore, the modified growth technique is a promising, convenient, new method for the growth of high-quality CdSe single crystals.     

Synthesis, growth, thermal, optical, dielectric and mechanical properties of semi-organic NLO crystal: Potassium hydrogen malate monohydrate

Potassium hydrogen malate monohydrate (PHMM), a semi-organic nonlinear optical material, has been synthesized and single crystals were grown from aqueous solution. Single crystals of PHMM have been grown by slow evaporation of solvent at room temperature up to dimensions of 22 mm×16 mm×14 mm. Single-crystal X-ray diffraction study on grown crystals shows that they belong to monoclinic system and non-centrosymmetry spacegroup Cc. The structural perfection of the grown crystals has been analyzed by high-resolution X-ray diffraction (HRXRD) rocking curve measurements. Fourier transform infrared (FTIR) spectroscopic study was performed for the identification of different modes of functional groups present in the compound. The UV–Vis transmission spectrum has been recorded in the range 200–1100 nm. The thermal stability of the compound has been determined by TG-DTA curves. The dielectric studies were performed. From the microhardness measurements, Vicker's hardness number (H_v), Stiffness constant (C₁₁), fracture toughness (k_c), Brittle index (B_i) and yield strength (σ_y) have been calculated. The Young's modulus was calculated using the Knoop hardness measurement. The SHG relative efficiency of PHMM crystal was found to be 1.2 times higher than that of KDP.     

Flux growth of BPO4 crystals

Single crystals of BPO₄ with sizes up to 15×10×12 mm³ were grown by top-seeded solution growth method using Li₂O–Li₄P₂O₇ as fluxes. The components volatilized from the melt were characterized by the method of X-ray powder diffraction. The defects of grown crystals have also been investigated. The measured ultraviolet cutoff edge of BPO₄ was about 130 nm. Its density was 2.82 g/cm³ determined using drainage method.     

Growth and morphology of ruby crystals with unusual chromium concentration

Single crystals of ruby have been obtained from fluxed melts based on the systems Li₂O–MoO₃, Li₂O–WO₃, Na₂O–WO₃, 2PbO–3V₂O₅, PbO–V₂O₅–WO₃, PbF₂–Bi₂O₃ and Na₃AlF₆ by both the TSSG method and spontaneous crystallization at the temperatures 1330–900 °C. Al₂O₃ solubility has been measured for the flux composition of 2Bi₂O₃–5PbF₂ in the temperature range 1200–1000 °C and dissolution enthalpy has been defined as 29.4 KJ/Mol. The composition of grown crystals was studied by electron microprobe analysis. The synthetic ruby contains from 0.51 to 6.38 at% of chromium admixture depending on the crystal growth conditions. Experimental results on growth conditions, composition and morphology of grown crystals are presented for each flux and temperature interval.