Horizontal Zone Melting Research Articles

The Features of Electronic Conduction in InAs

The electrical properties of n-type crystals of InAs compound, grown from stoichiometric melt by the horizontal zone melting method, have been investigated in the temperature range of 4.2 K-300 K before and after fast neutron irradiation up to high integral fluences of 2×1018n?cm-2. At a fixed temperature electrons concentration (n) increases almost by one order during irradiation, and practically does not change with increasing of temperature. n increases only slightly by increasing of temperature near 300 K, both before and after irradiation. When ? 4×1018cm-3 the change of during irradiation is negligible. Comparison of experimental data of mobility with theory shows that the privileged scattering mechanism of electrons at 300 K is scattering on optical phonons in InAs with 1016-1017 cm-3 and scattering on ions of impurity in InAs with n~1018-1019 cm-3. The analysis shows that during irradiation point type scattering centers of donor-type structural defects with shallow levels in the forbidden zone appear. Consequently, the mobility decreases during irradiation. At 300 K in sample with electrons concentration of 3×1016 cm-3 the mobility decreases by 5 times after irradiation, which is equivalent to the formation of 1.5×1019cm-3 charged point scattering centers.

The Features of Electronic Conduction in InAs

The electrical properties of n-type crystals of InAs compound, grown from stoichiometric melt by the horizontal zone melting method, have been investigated in the temperature range of 4.2 K-300 K before and after fast neutron irradiation up to high integral fluences of 2×1018n∙cm-2. At a fixed temperature electrons concentration (n) increases almost by one order during irradiation, and practically does not change with increasing of temperature. n increases only slightly by increasing of temperature near 300 K, both before and after irradiation. When ≥ 4×1018cm-3 the change of during irradiation is negligible. Comparison of experimental data of mobility with theory shows that the privileged scattering mechanism of electrons at 300 K is scattering on optical phonons in InAs with 1016-1017 cm-3 and scattering on ions of impurity in InAs with n~1018-1019 cm-3. The analysis shows that during irradiation point type scattering centers of donor-type structural defects with shallow levels in the forbidden zone appear. Consequently, the mobility decreases during irradiation. At 300 K in sample with electrons concentration of 3×1016 cm-3 the mobility decreases by 5 times after irradiation, which is equivalent to the formation of 1.5×1019cm-3 charged point scattering centers.

Development and melt growth of novel scintillating halide crystals

Melt growth of scintillating halide crystals is reviewed. The vertical Bridgman growth technique is still considered as very popular method that enables production of relatively large and commercially attractive crystals. On the other hand, the micro-pulling-down method is preferable when fabrication of small samples, sufficient for preliminary characterization of their optical and/or scintillation performance, is required. Moreover, bulk crystal growth is also available using the micro-pulling-down furnace. The examples of growths of various halide crystals by industrially friendly melt growth techniques including Czochralski and edge-defined film-fed growth methods are also discussed. Finally, traveling molten zone growth that in some degree corresponds to horizontal zone melting is briefly overviewed.

Electrochemical Reduction of Solid Silica to Form Silicon in Molten Salts

Nowadays, Silicon is the most critical element in solar cells and/or solar chips. Silicon having 98 to 99% Si as being metallurgical grade, requires further refinement/purification processes such as zone refining [1,2] and/or Siemens process [3] to upgrade it for solar applications. A promising method, based on straightforward electrochemical reduction of oxides by FFC Cambridge Process [4], was adopted to form silicon from porous SiO2 pellets in molten CaCl2 and CaCl2-NaCl salt mixture [5]. It was reported that silicon powder contaminated by iron and nickel emanated from stainless steel cathode, consequently disqualified the product from solar applications. SiO2 pellets sintered at 1300oC for 4 hours, were placed in between pure silicon wafer plates to defeat the contamination problem. Encouraging results indicated a reliable alternative method of direct solar grade silicon production for expanding solar energy field.[1] P.R. Mei, S.P.Moreira, E.Cardoso, A.D.S.Cortes, F.C.Marques, “Purification of metallurgical silicon by horizontal zone melting”, Sol. Energ. Mat. Sol., 98 (2012), 233-239. [2] P. Siffert, E.F. Krimmel, eds. Silicon: Evolution and future of a technology. Berlin,Springer (2004). [3] Siemens & Halske: BRD Patents 1.102.117 and 1.140.1594 filed 1954, issued 1956 [4] G.Z. Chen, D. J. Fray, T. W. Farthing, “Direct Electrochemical Reduction of Titanium Dioxide to Titanium in Molten Calcium Chloride”, Nature, 407 (2000), 361-364. [5] E. Ergül, İ. Karakaya, M. Erdoğan, “Electrochemical decomposition of SiO2 pellets to form silicon in molten salts” Journal of Alloys and Compounds, 509 (2011), 899-903.

In Search of an Alternative Solar Grade Silicon Production By Electrochemical Reduction of SiO2

Silicon plays an important role in fabrication of solar cells and solar chips. Metallurgical grade silicon (98 to 99 % Si) demands further purification such as zone refining [1, 2], metallothermic reduction [3] and Siemens process [4] to convert it to solar grade. A promising method, based on direct electrochemical reduction of oxides by FFC Cambridge Process [5], was adopted to form silicon from porous SiO2 pellets in molten CaCl2 and CaCl2–NaCl salt mixture [6]. The contamination of silicon powder by iron and nickel originating from stainless steel cathode was reported to disqualify the product from solar applications. SiO2 pellets, sintered at 1300oC for 4 hours, were sandwiched between pure silicon wafer plates to minimize contamination of silicon. The promising results indicated a potential alternative method of direct solar grade silicon production for expanding solar energy industry. [1] P.R. Mei, S.P.Moreira, E.Cardoso, A.D.S.Cortes, F.C.Marques, “Purification of metallurgical silicon by horizontal zone melting”, Sol. Energ. Mat. Sol., 98 (2012), 233-239. [2] P. Siffert, E.F. Krimmel, eds. Silicon: Evolution and future of a technology. Berlin,Springer (2004). [3] K. Yasuda, T.H. Okabe, “Solar-grade silicon production by metallothermic reduction”, JOM,62 (12) (2010), 94-101. [4] Siemens & Halske: BRD Patents 1.102.117 and 1.140.1594 filed 1954, issued 1956 [5] G.Z. Chen, D. J. Fray, T. W. Farthing, “Direct Electrochemical Reduction of Titanium Dioxide to Titanium in Molten Calcium Chloride”, Nature, 407 (2000), 361-364. [6] E. Ergül, İ. Karakaya, M. Erdoğan, “Electrochemical decomposition of SiO2 pellets to form silicon in molten salts” Journal of Alloys and Compounds, 509 (2011), 899-903.

Hypereutectic Al2O3/YAG/ZrO2 In Situ Composite Prepared by Horizontal Laser Zone Melting

Abstract Al2O3/YAG/ZrO2 eutectic in situ composite has now been considered as the new generation of high-temperature structural material due to its excellent performance even close to its melting point. In this work, hypereutectic Al2O3/YAG/ZrO2 in situ composite is manufactured by the horizontal laser zone melting technique. The relationship between the solidification microstructure and the solidification parameters is studied. The minimum lamellar spacing is as finer as 0.20 μm when the laser scanning rate is 800 μm/s. Compared with eutectic Al2O3/YAG/ZrO2, hypereutectic exhibits more regular and finer microstructure at the similar conditions. Meanwhile, it is found that the lamellar spacing remains almost as constant at a certain high solidification velocity. The maximum hardness and fracture toughness are 15.9 GPa and 4.2 MPa · m1/2, respectively.

Purification of metallurgical silicon by horizontal zone melting

In this study, we aimed at systematically determining the potential of the zone melting (ZM) technique to remove impurities from Metallurgical Grade Silicon (MG- Si) in an Electron Beam Furnace (EBF), using a water-cooled copper crucible. Our focus was on obtaining solar grade silicon, with the purity between Electronic Grade Silicon (EG-Si) and MG-Si, at lower cost than the silicon obtained by the Siemens process. The MG- Si (99.855% purity in mass, or 1,450ppm of impurities) was processed by 1 and 2 passes of ZM at speed of 1mm/min and 10mm/min. The ZM process reduced in 98% the total amount of impurities present in the MG-Si, increasing the purity from 99% to 99.999%, an intermediate stage to achieve the electronic grade (> 99.9999%). Boron remained near the same after the ZM due to its vapor pressure be lower than the pressure of the furnace chamber and due its distribution coefficient in silicon be near the unit. Carbon and oxygen in the MG-Si were reduced from 106 to 35ppm and from 30ppm to 5ppm, respectively, after ZM, and these values are very close to the levels in the electronic grade silicon. The electrical resistivity showed to be dependent on the boron concentration, but not on the phosphorus or the total amount of impurities. All ingots processed by ZM exhibited p-type characteristics, and it means that boron was really the dominant dopant.

Dislocation, annealing and quenching effects on the microindentation hardness of Bi 2Te 3 and Bi 2Te 2.9Se .1 single crystals

Stoichiometric crystals of Bi 2Te 3 and Bi 2Te 2.9Se .1 have been grown from the melt by the horizontal zone melting (HZM) technique. X-ray powder diffraction and energy dispersive X-ray analysis could prove that the grown crystals are stoichiometric with lattice constants a=0.4374 nm, c=3.044 nm for Bi 2Te 3 and a=0.4374 nm, c=3.038 nm for Bi 2Te 2.9Se .1. Dislocation density measurements are carried out by etch pit technique and are observed by scanning electron and optical micrograph. The mechanical strength of the as-grown, quenched and annealed crystals is assessed by the Vickers hardness measurements.

Interface control mechanisms in horizontal zone-melting with slow rotation

Using slow rotation to control the interfaces in horizontal zone-melting (HZM) is a widely adopted method for organic materials, i.e., the Pfann–Miller technique. A short and nearly axisymmetric zone can be achieved easily even with a rotation rate of only 1 or 2 rpm. However, the melt convection might not be the crucial mechanism for such a control. Through flow and interface visualization during HZM of succinonitrile, the role of the slow rotation was investigated. Three-dimensional numerical simulation was further performed to illustrate the key mechanisms for determining the zone shape. Besides the good agreement between the simulation and the experiments, we found that the heat of fusion released or absorbed during the rotational regrowth and remelting played a crucial role, and it could not be ignored in the simulation.

Phase and chemical composition of the zone melted Bi 2Sr 2CaCu 2O rods

The influence of the horizontal zone melting arrangement on the resulting phase and chemical composition of the Bi 2.1Sr 1.9CaCu 2O 8 rods was investigated. It was found that already in the as grown state the main middle part of the examined rods is formed predominantly by aligned grains of 2212 phase exhibiting a uniform composition.

The growth of homogeneous semiconductor crystals in a centrifuge by the stabilizing influence of the Coriolis force

Both experimental and numerical results on crystal growth and fluid flow studies carried out in a centrifuge are reported. It is shown that the formation of doping striations can be avoided in the vertical Bridgman and the horizontal zone melting growth of Te-doped InSb if the centrifugal acceleration is increased beyond a critical value depending on the thermal boundary conditions. Furthermore, the maximum rate for the growth of inclusion free GaSb crystals grown by the travelling heater method (THM) is increased by a factor of 10 if this method is carried out at an acceleration of 20 times earth gravity. Model experiments in the Bridgman configuration using a test cell with liquid Ga and a larger series of thermocouples are conducted by varying the thermal boundary conditions and the rotation rate of the centrifuge. A three-dimensional time dependent numerical simulation of the fluid flow under the experimental conditions was carried out using a finite difference numerical scheme. It follows clearly that the Coriolis force acting on the melt in the rotating centrifuge system significantly influences the buoyancy-driven convection with respect to the flow patterns as well as the stability. The Coriolis force causes two very different flow states (I and II), depending on whether the rotation sense of the flow is in the same or in the opposite direction to that of the centrifuge. Type I is very similar to that normally observed on earth. Type II is only observed on the centrifuge and has a very large stability range of steady convection which can be used to grow striation-free crystals. All results give excellent agreement between model experiments and numerical calculations, which finally leads to a fully satisfying explanation of the crystal growth results on our centrifuge.

Laser performance of LiSrAlF6:Cr3+

We have lased the new material, LiSrAlF6:Cr3+ (Cr3+:LiSAF). The single crystals were grown by the horizontal zone melting technique. The spectroscopic properties of Cr3+:LiSAF are similar to those of other low-field Cr3+-doped systems, although the emission cross section is strongly π polarized and is also somewhat larger than has been measured for other fluoride hosts. The free-running lasing wavelength of Cr3+:LiSAF is 825 nm, and the tuning range extends from at least 780 to 920 nm. Using Kr laser pumping, we obtained slope efficiencies of 36% and 14% by utilizing output couplings of 4.8% and 0.8%, respectively. On the basis of these results, the extrapolated maximum efficiency of 53% is determined, to be compared to the quantum defect-limited value of 78%. It is concluded that a moderate level of excited state absorption (ESA) loss is responsible for the reduced efficiency of the Cr3+:LiSAF system. This contrasts with the related results previously obtained for LiCaAlF6:Cr3+, where it was concluded that the effects of ESA were negligible [IEEE J. Quantum Electron. QE-24, 2243 (1988)].

Elaboration of high purity iron (RRR>4000) by horizontal zone melting—attempts for chemical characterization

High purity iron bars were prepared by horizontal zone melting in a water cooled copper boat. The bar is zone melted five times under helium and five times under dry hydrogen. In order to characterize the metal, RRR measurements were performed on cold rolled and annealed samples in dry and wet hydrogen. The RRR measurements vary with the water content of hydrogen: 2734 after dry annealing, 4287 after wet annealing. The RRR variation cannot be related to titanium, chromium, copper or manganese internal oxidation, but to that of aluminium and silicon. After chemical polishing, RRR measurements increase by about 2000 points. If we want to adopt the RRR measurement as a purity criterion of the samples, the surface treatments and the annealing conditions have to be stated. We tried to connect the RRR to the chemical purity of the material. Considering the present analysis capabilities and the high purity metal degree involved, it seems difficult to directly connect the RRR measurements to the variation of the chemical impurities contents.

Identification and characterization of precipitates in (Gd,Ho)-doped GaSb crystal

Abstract Two types of precipitate were identified in gallium antimonide heavily doped with Gd and Ho. The crystal has been grown by the horizontal zone melting method. It was confirmed that one type of precipitate corresponded to Gd 0.44 Ho 0.56 Sb mainly, and the other type to HoSb. Both types of precipitate also contain compounds of doped rare earth elements with oxygen and carbon. Identification of these precipitates was carried out using EPMA and X-ray diffraction technique. Characterization of the precipitates was performed by SEM and XES.

Programmed crystal growth on a diffractometer with focused heat radiation

To improve the growing of single crystals for structural analysis, especially those of low-melting-point materials, a new technique and the appropriate apparatus have been developed. The heat radiation of a halogen lamp of adjustable intensity is focused by a parabolic mirror on the sample capillary, which is mounted on a diffractometer and cooled by a gas stream at a controlled temperature. The focus can be moved along the length of the capillary in any direction, for horizontal or vertical miniature zone melting or Bridgman techniques. The heat source and the movable mirror are controlled by a microprocessor, which allows systematic and software-supported search and reproduction of suitable experimental growing conditions.

Suppression of doping striations in zone melting of InSb by enhanced convection on a centrifuge

An experimental study of convective effects in horizontal zone melting of InSb at large inertial accelerations (up to 30 times earth gravity) is reported. The experiments were carried out on a centrifuge arrangement which permits to vary the driving force of convection in a wide range. The occurrence of temperature fluctuations in the melt zone and of doping striations in the growing crystal is investigated in dependence on resulting acceleration. This is explained by unsteady convection which is discussed in relation to existing theoretical work. A suppression of unsteady convection and doping striations at large acceleration is reported which has been observed for the first time in horizontal zone melting.

Horizontal Zone-Melting of Indium Antimonide in Vacuum. II. Characterization by Galvanomagnetic Measurements at 77 K

Magnetoresistance and transverse magnetophonon resonance data at 77 K for n-type InSb crystals (prepared by the method described in Part I) are given, with the aim of detecting residual impurities and inhomogeneities. The importance of 1) using boat material not wetted by InSb and 2) low-temperature annealing (at 200°C for one week) are shown experimentally. The concentration of residual impurities is estimated to be 2×1014/cm3, and three kinds of impurity are found. Furthermore, dislocations and non-uniform distribution of the compensating acceptor impurities are identified as the source of inhomogeneities. It is concluded that the carrier concentration of less than 1014/cm3 is due to the compensation effect and that the reliable maximum mobility at 77 K is 8×105cm2/V·s.

Single crystal growth by the horizontal levitation zone melting method

The method used to prepare large single crystals of some rare earth metals and intermetallic compounds is described. A levitated molten zone is passed along a rod shaped sample which is contained in a cold crucible in the horizontal position. The high frequency power system used to both create and levitate the molten zone is also described. The conditions required to grow crystals larger than one cubic centimeter of both incongruwnt and congruent melting compounds are given. The quality and some pertinent property values of the crystals as determined by X-ray and metallographic methods are included.

Interaction of Copper with Lead during their Mass Transfer in the Horizontal Zone Melting of Tin

Interaction of Copper with Lead during their Mass Transfer in the Horizontal Zone Melting of Tin

The purification and crystal growth of lithium chloride

A four-step procedure for the purification of LiCl is described embodying: (1) solvent extraction, (2) vacuum dehydration, (3) halogen treatment of the molten salt, and (4) horizontal zone melting. Zone refining, by itself, does not yield salt of high purity since several contaminating cations are found to have effective segregation coefficients (k∗) greater than or close to unity. Fe, Co, Ni and Ca have k∗ values of 2.0, 1.9, 2.6 and 0.9 respectively. Preliminary purification by solvent extraction reduces Fe and Ni to < 0.1 μg/g and Ca to < 1.0 μg/g. Treatment of the melt with Cl 2 and HCl reduces the initial 50 μg/g Br − contamination to < 0.1 μg/g. Final purification by zone melting results in an impurity level of ∼ 0.5 μg/g for Na and < 0.1 μg/g for the remaining alkali metals. Oscillator strengths for Fe and Ni impurity-absorption bands in LiCl are also presented.