Floating-zone growth of GaAs under microgravity during the D2-mission

A Te-doped GaAs (100) single crystal of 20 mm diameter and 20 mm length was successfully grown by the floating-zone method during the 2nd German Spacelab mission D2. Dopant striations due to Marangoni convection as well as a reduction of the etch pit density compared to te starting material have been found. The last part of the crystal, grown with the quite high translation rate of 120 mm/h, showed no sign of unstable growth and exhibited properties similar to the parts grown with 3 and 6 mm/h.     

Vertical optical floating zone furnace: Principles of irradiation profile formation

The light distribution within the vertical double-ellipsoid mirror furnace applied for floating zone crystal growth with optical heating is studied. During the last few years, this setup was intensively applied for crystal growth of intermetallic and oxide materials due to its advantages for radiation focussing, which is superior in some key features compared to other commercial horizontal and vertical optical floating zone facilities. A point source model was used as a light source to reveal basic principles of the irradiation profile formation, which can strongly affect the melt flows, as well as the curvature and stability of crystallization front. Effects of the lamp displacement along the vertical optical axis with respect to the focal point of the lower elliptical mirror and the effect of mirror apertures were studied as the prime factors, which determine the light profile on the crystal. The efficiency of the light focusing in the presented optical configuration is discussed.     

Long-term Crystal Growth under Microgravity during the EURECA-1 Mission (I) THM Growth of AlxGa1−xSb

Long-term crystal growth experiments were successfully performed under microgravity conditions during the first flight of the unmanned mission EURECA-1 in the automatic mirror furnace (AMF). Two crystals of Al_xGa_1−xSb with [001] and [111] orientation respectively were grown from gallium solution by the travelling heater method. The grown length of the single crystals is 4.0 mm and 4.2 mm respectively. The space-grown samples show a high microscopic homogeneity which indicates the absence of time dependent convection. From pulse markers a constant growth rate of 0.6 ± 0.1 μm/min is measured which is lower than 0.8 ± 0.1 μm/min obtained in earth grown reference samples. Details about the experiment performance and the growth results are given.     

Formation of microdefects in semiconductor silicon

The distribution patterns and physical nature (the sign of the lattice strain) of growth microdefects in dislocation-free Si single crystals grown by the floating-zone and Czochralski methods were studied by selective etching and transmission electron microscopy. Mechanisms of formation and transformation of growth microdefects, depending on the crystal growth rate, are proposed. A heterogeneous mechanism of formation of microdefects is considered.     

Earth optimization of space experiment on growth of germanium by floating-zone technique with the use of rotating magnetic fields

The results are considered of the earth experiments on growth of high-purity and Ga-doped germanium single crystals 15 mm in diameter and 60 mm in length, which were performed in a Zona-4 “space furnace” under the technological regimes close to those existing in space orbits. It is shown that the use of a magnetohydrodynamic (MHD) factor [weak (0.15–0.2 mT) rotational (400 Hz) magnetic fields] during crystallization of semiconductors by the floating-zone technique is a very promising method for control of dopant distributions and electrophysical properties in a growing crystal. It is shown that in such magnetic fields, the effective coefficient of Ga distribution in Ge decreases by 10%. The shift of the donor-acceptor balance of the residual dopants in a compensated semiconductor during growth with the MHD-stirring of the melt was first established in growth of undoped germanium single crystals. It was also established that magnetic fields produce different effects on the resistivity microinhomogeneity in undoped and doped crystals. The mechanisms of the MHD effect on the properties of the grown crystals are discussed as well as the perspectives of performing analogous experiments aboard spacecrafts. It is predicted that, under the microgravitation conditions, the effects revealed in terrestrial experiments would be more pronounced.     

Growth of pyroxene-type MnGeO3 and (Mn,Mg)GeO3 crystals by the floating-zone method

Pyroxene-type solid–solution crystals of (Mn_1−xMg_x)GeO₃ with x=0.06, 0.10 and 0.20 have been grown by the floating-zone method. The end member crystal of MnGeO₃ is broken into small pieces by the orthorhombic-to-monoclonic phase transition during cooling after growth. On the other hand, the solid–solution crystals keep the orthorhombic structure between the melting points and room temperature and no crack is formed. The unit cell volumes are significantly decreased with an increase in Mg content.     

Long-term Crystal Growth under Microgravity during the EURECA-1 Mission (II) THM Growth of Sulphur-doped InP

Long-term crystal growth experiments were successfully performed under microgravity conditions during the first flight of the unmanned EURECA-1 mission in the automatic mirror furnace (AMF). Two crystals of sulphur-doped InP with [001] and [111] orientation respectively were grown from indium solution by the travelling heater method (THM). The absence of time dependent buoyancy-driven convection is documented by the lack of type I striations in the space-grown crystals. The sulphur concentration is measured by spatially resolved photoluminescence. As expected, the macrosegregation can be described by a pure diffusion-controlled model which is in good agreement with the findings from the first German spacelab mission D1. Compared to the earth-grown reference samples, both of the space-grown InP crystals show strong disturbances such as inclusions and type II striations. The morphological instabilities are similar to growth disturbances already known from the space-grown MD-ELI-01 from the D1 mission.     

Modulating dopant segregation in floating-zone silicon growth in magnetic fields using rotation

The feasibility of modulating dopant segregation using rotation for floating-zone silicon growth in axisymmetric magnetic fields is investigated through computer simulation. In the model, heat and mass transfer, fluid flow, magnetic fields, melt/solid interfaces, and the free surface are solved globally by a robust finte-volume/Newton's method. Different rotation modes, single- and counter-rotations, are applied to the growth under both axial and cusp magnetic fields. Under the magnetic fields, it is observed that dopant mixing is poor in the quiescent core region of the molten zone, and the weak convection there is responsible for the segregation. Under an axial magnetic field, moderate counter-rotation or crystal rotation improves dopant uniformity. However, excess counter-rotation or feed rotation alone results in more complicated flow structures, and thus induces larger radial segregation. For the cusp fields, rotation can enhance more easily the dopant mixing in the core melt and thus improve dopant uniformity.     

Growth of cobalt single crystals by the Electron beam floating-zone method

Co single crystals of striation-free were grown easily by the electron-beam floating-zone melting. For these crystals, observations on dislocations were carried out. Slight preferred direction of grown crystals were discussed on the basis of the local step structure on the crystal surface.     

φ200mm蓝宝石晶体生长工艺研究

采用单晶提拉炉成功生长出φ200mm ×180mm大尺寸Al2O3晶体.探讨了晶体生长工艺参数和晶体开裂之间的关系,并讨论了晶体中的热应力、热应变、温度梯度、提拉速度之间的关系,分析了影响晶体质量主要是晶体开裂的原因,设计出生长大尺寸Al2O3晶体的最佳工艺条件.     

Comparison of Ba(B1-xAlx)2O4 Single Crystals on their Diameters

Small diameter crystals of Ba(B_1-xAl_x)₂O₄ were grown by Floating zone pulling down method and Micro-pulling down method to be compared with large diameter crystals grown by Czochralski method. While the Czochralski grown crystal was opaque, the crystal transparency was actually improved with the decrease of crystal diameter, i.e., the decrease of constitutional supercooling. The reason was the increase of temperature gradient caused by down-sizing of the crystal diameter deduced by down-sizing of the growth furnace. The adequate diameter for transparent crystal was determined depending on the Al content.     

Optimization of control parameters of cadmium zinc telluride Bridgman single crystal growth

The temperature gradient within a furnace chamber and the crucible pull rate are the key control parameters for cadmium zinc telluride Bridgman single crystal growth. Their effects on the heat and mass transfer in front of the solid‐liquid interface and the solute segregation in the grown crystal were investigated with numerical modeling. With an increase of the temperature gradient, the convection intensity in the melt in front of the solid‐liquid interface increases almost proportionally to the temperature gradient. The interface concavity decreases rapidly at faster crucible pull rates, while it increases at slow pull rates. Moreover, the solute concentration gradient in the melt in front of the solid‐liquid interface decreases significantly, as does the radial solute segregation in the grown crystal. In general, a decrease of the pull rate leads to a strong decrease of the concavity of the solid‐liquid interface and of the radial solute segregation in the grown crystal, while the axial solute segregation in the grown crystal increases slightly. A combination of a low crucible pull rate with a medium temperature gradient within the furnace chamber will make the radial solute segregation of the grown crystal vanish. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Preferred Growth Direction of Ni Single Crystals by the Floating-Zone Method

In Ni single crystals grown by the floating-zone method, it was found that their growth directions tended to concentrate towards the 〈111〉 or the 〈100〉 direction. An interpretation was put forward for the preferred direction of these crystals in terms of thermal stability of the crystallographic planes in the solid-liquid interface.     

大尺寸氟化钡晶体的生长

通过软件模拟设计合理的炉体温场结构,并对晶体原料的提纯及生长工艺条件进行优化,采用改进的坩埚下降法成功地制备出了大尺寸、高质量的氟化钡晶体.晶体的透过率在0.2 ～10 μm波长范围内高于85;,最高透过率约为94;.     

冷心放肩微量提拉法大尺寸蓝宝石单晶生长过程的模拟分析

利用数值模拟方法计算了冷心放肩微量提拉法(SAPMAC)蓝宝石晶体生长过程.结合晶体直径变化、裂纹出现位置与延续方向、晶体透明性等实验现象,通过与提拉法、温梯法、坩埚移动法等相对比,分析了冷心放肩微量提拉法晶体生长各阶段的工艺特点,并根据模拟计算结果对晶体生长系统和晶体生长控制工艺进行了改进.分别利用增大热交换器的散热参数、降低加热温度、改进降温曲线、调节外加轴向和径向温度梯度的方式来实现对晶体生长的引晶、放肩、等径和收尾控制.通过实验比较证明了改进后的晶体生长系统和晶体生长控制工艺能够生长出性能较好的大尺寸蓝宝石晶体.     

提拉法生长镓酸锂晶体及缺陷研究

研究了提拉法生长的镓酸锂单晶的生长习性和结晶质量.晶体表面呈乳白色且表面粗糙.通过光学显微镜、四晶X射线衍射、透射光谱和电感耦合等离子体发射光谱对样品进行了表征,结果表明,在(001)面的抛光样品上存在三种缺陷: [110]和[-110]方向的十字线、[010]方向排列的气泡包裹物以及平行于(010)面的界面,界面的产生起因于(010)晶面的滑移;晶体的结晶质量从顶部到底部逐渐下降,这是由于在生长过程中氧化锂的挥发导致熔体成分偏离化学计量比造成的.     

Cu单晶的生长与温场研究

Cu单晶在中子单色器、激光核聚变和音频信号传输等方面有着广泛的应用前景.根据对Cu晶体的差热分析结果,设计并制作了硅钼棒加热单晶生长炉,获得了适合Cu单晶体生长的温场.采用改进的垂直布里奇曼法成功生长出外观完整、表面光滑、尺寸为15 mm×35 mm的Cu单晶体.对生长的晶体进行切割、抛光腐蚀后,采用金相显微镜和X射线衍射分析,结果表明:研究设计的温场适合Cu单晶体的生长,生长出的晶体结晶性好、结构完整.     

Micrometric single crystal germanates obtained using a double‐spherical mirror furnace

Micro‐crystals of two new compounds EuMnGe₂O₇ and SmMnGe₂O₇ were grown performing the flux method in a double‐spherical mirror furnace. One valuable advantage of this system was that the heating profile could be modified easily adjusting lamp positions and orientation as well. The micrometric crystals were observed and analyzed for chemical composition by scanning electron microscopy and energy dispersive spectroscopy. This furnace is perfectly suitable to grow at low price, low temperature and short time new materials as a single crystal for basic research or to obtain raw material. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

On the Design of Double‐Ellipsoid Mirror Furnace and its Thermal Characteristics for Floating‐Zone Growth of SrxBa1‐xTiO3 Single Crystals

We have designed a double ellipsoid mirror furnace for floating‐zone crystal growth using lamps with rectangular filaments. Its thermal characteristics were studied using an alumina tube for several system configurations. A simple comparison with a commercial furnace that used cylinder lamps for the heating profile was also conducted. By adjusting lamp orientation and positions, one could modify heating profiles easily. In general, the thermal characteristics of the furnace were consistent with the model's prediction [J. Crystal Growth 173 (1997) 561]. The effects of growth chamber and heat pipe were further illustrated. Furthermore, a suitable system configuration leading to better heating uniformity and lower thermal gradients near the growth interface was found for the floating‐zone growth of Sr_xBa_1‐xTiO₃ single crystals.     

Solutal convection during growth of organic NLO crystals

Effect of solutal and thermal convection plays very important role when a large thermal gradient is applied during crystal growth. To address this problem, we have purified m.nitroaniline (m.NA) and m. dinitrobenzene (m.DNB) and studied crystal growth and effect of growth parameters on the optical quality. Crystals of pure and binary alloy of m.dinitrobenzene and m.nitroaniline were grown by vertical directional solidification method in a two zone transparent furnace. Effect of doping and temperature gradient on the solid-liquid interface morphology and quality of crystal was determined by studying the bulk transparency and nonlinearity.