Distribution of the gibbs activation energy for formation of a kink around the top of the growth hills of the face (001) of TGS single crystal

The shape of the vicinal hills of growth of the (001) face of the TGS single crystal was investigated by a laser Michelson interferometer. It was found that the distribution of the Gibbs activation energy for formation of a kink is not equivalent around the top of the hill.     

Geometrical aspect of the problem of model structure growth

In developing the representation of model growth of crystalline and quasicrystalline structures in the form of a growing graph, the convolution operation is used to describe the formation of the growth polyhedron from a specified system of bonds (direct growth problem). It is shown that the growth polyhedron is formed by a system of intermolecular interactions so that the main bonds, which determine the neighborhood graph of the molecules of this system, are oriented in the direction of the growth polyhedron vertices. It is shown that the system of molecular bonds can be determined on the basis of the growth polyhedron (inverse growth problem).     

Determination of linear growth rates of crystals (I). Calculation of linear growth rates of individual crystal faces from overall rates

The presented paper (Part I and II) is devoted to the fundamental principles of the kinetics of crystal growth. The number of studies in this field has been increasing and some authors have introduced different terms and definitions. To avoid possible mistakes and confusions, the individual definitions of the rate of crystal growth are specified and their interrelations are discussed in detail. Basic methods for measuring the kinetics of crystal growth are described. The rate of growth of individual crystal faces or the average rate of crystal growth can be determined using the selected experimental method. The presented study demonstrates that the results obtained by either of the two measuring methods (linear rate of growth of crystal faces and average rate of crystal growth) can be interrelated. The established method of calculating linear growth rates of individual crystal faces is based on an analysis of the time dependence of the volume of a growing crystal. The relationship between the linear growth rates of individual crystal faces and the over-all crystal growth rate is presented and a method for assessing the linear growth rates of individual crystal faces from over-all growth rate data, which can be measured readily, is suggested.     

Modelling of Growth Rate for MSMPR Crystallizer Data

One of the most important applications of the population balance approach to MSMPR crystallizer modelling is the recovery of crystal nucleation and growth rates data from steady-state crystal size distributions (RANDOLPH, LARSON). A large number of studies have confirmed that both size-dependent (growth rate is a function of crystal size) and growth rate dispersion (crystals of the same size do not have the same growth rate), causes nonlinearities which limit the usefulness of the RANDOLPH and LARSON approach. A discussion of modelling of crystal growth kinetics for simulated and real MSMPR crystallizer data is presented. In the former case, both linear and non-linear log population density distributions are used. The modelling of growth kinetics is done twice – once assuming that growth rate dispersion is a source of curvature in the log population density vs size data plot and, again when this curvature is caused by size-dependent growth. Calculations clearly indicate that even for crystallizing systems which follow the McCabe's δL law, both growth rate dispersion and size-dependent growth models lead to proper estimation of growth kinetics. When log population density vs size data plots exhibit curvature, however, use of the size-dependent growth rate approach gives more reliable growth kinetics across a broad crystal size range than those obtained from modelling of growth kinetics by growth rate dispersion.     

Iso-epitaxial growth of n-octacosane crystals

Iso-epitaxial(epilayer)growth of n-octacosane crystals is reported. The morphology of the epilayers is in the form of triangular growth islands with or without truncature. Epilayer growth precedes spiral growth mechanism which occurs at medium and low supersaturations, respectively. The occurrence of triangular and truncated rhombic platelets is found to be a manifestation of growth at medium supersaturations.     

L-苹果酸脲光学晶体的台阶生长机制

L-苹果酸脲是一种新型的有机非线性光学晶体,具有广阔的应用前景.研究表明,L-苹果酸脲晶体在乙醇介质中生长时,晶体形态为棱柱形.L-苹果酸脲晶体生长呈现明显的台阶生长,当过饱和度比较低时,其台阶生长机制为螺旋机制;当过饱和度较大时,L-苹果酸脲晶体台阶生长机制为二维成核机制.     

PVT法同质外延制备大尺寸Al极性氮化铝晶体生长工艺及其表征分析研究

本文基于自主设计的氮化铝生长炉,开展了四组不同工艺条件下Al极性面氮化铝籽晶同质外延生长氮化铝单晶的生长特征及其结晶质量表征研究。研究发现:不同工艺条件下生长的晶体的拉曼图谱E₂(high)特征峰峰位表明,晶体内部均存在较小的拉应力;在坩埚顶部在相对较高温度2 210 ℃、坩埚底部与顶部温差42 ℃的低过饱和度生长条件下,晶体表面光滑,呈现阶梯流生长形貌,并具有典型的氮化铝单晶生长习性面,晶体初始扩张角大于40°,高分辨率X射线衍射(HRXRD)测得0002、1012反射摇摆曲线及拉曼光谱检测结果表明,该条件下生长的氮化铝晶体结晶质量优异,并可实现快速扩径。基于该生长条件,通过外延生长后成功获得尺寸ϕ45~47 mm的氮化铝单晶锭,相关表征结果表明生长的氮化铝晶体具有优越的结晶性能。     

大尺寸晶体快速生长理论与技术的研究进展

“如何突破大尺寸晶体材料的制备理论和技术”是中国科协发布的2021年度的十大前沿科学问题之一,揭示晶体生长机制和突破生长关键技术是大尺寸功能晶体发展的两个趋势。在原子分子尺度上,晶体生长可以是有势垒的热激活过程,也可以是无势垒的超快结晶过程,这与具体的体系以及晶面有关。从界面属性角度来看,光滑界面是以台阶拓展的方式生长;粗糙界面没有明显的固-液分层,通过局部原子固化进行生长。本文从晶体生长理论模型、生长技术及其应用实例,以及分子动力学方法在晶体生长中的应用等方面探讨了近些年大尺寸晶体快速生长理论和技术的研究进展。目前有多种方法制备大尺寸晶体,但普遍存在制备的晶体质量差和性能不稳定等问题。需要突破对晶体生长微观机制上的认识,建立机制与温度、流速等外界因素的内在联系。而利用机器学习力场以及分子动力学模拟方法,建立固-液界面,模拟晶体生长,将是探究晶体生长微观机制的一种有效方式。     

Change of the Normal Rate of Hills Growth on the (001) Face of TGS Single Crystal Under Constant Crystallization Conditions

Considerable change (up to 100% in one of the cases) of the normal growth rate of hills on the (001) face of the TGS crystal at strictly constant supersaturation and temperature is registered experimentally. On the basis of the spatial disposition of the dislocations, which form the source of the steps, a model of a growth centre (called herein non-parallel centre of growth) is proposed. The model is qualitatively concordant with the experimental data. It is shown that the inconstancy of the normal rate of growth at constant supersaturation and temperature is an immanent characteristic of the non-parallel centre of growth.     

Three-dimensional simulation of floating-zone crystal growth of oxide crystals

The floating-zone (FZ) method is a popular technique for the growth of high-temperature oxide crystals. However, the growth usually requires skillful control of the zone stability, which is strongly coupled with heat flow, interfaces, and the grown crystal morphology. In this report, we present a three-dimensional self-consistent simulation of floating-zone oxide growth in a mirror furnace by taking these factors into account simultaneously. This model is based on an efficient finite volume method with multigrid acceleration and interface tracking. The steady growth of a YAG crystal in a double-ellipsoid mirror furnace is taken as an example to illustrate the intricate coupling of convection, interfaces, meniscus, and the grown crystal shape.     

Output power enhancement of 100% for quaternary GaInAsSb/AlGaAsSb semiconductor disc lasers grown with a sequential growth scheme

Molecular beam epitaxial (MBE) growth and lasing operation of quaternary GaInAsSb/AlGaAsSb-based optically-pumped vertical-external-cavity surface-emitting lasers (VECSEL) emitting at a wavelength of 2.0 μm are reported. MBE growth of such structures is particularly challenging as it requires, apart from the large total thickness of the epitaxial layer stack of 10–12 μm a change of group-III fluxes for the growth of AlAsSb and low Al-content AlGaAsSb. Two different growth schemes are compared. The first one is the conventional growth procedure in which the wafer remains in the growth chamber and the growth is interrupted at the interfaces before and after the active region to adjust the group-III cell temperatures for different flux settings. At the interfaces where the growth had to be interrupted, secondary-ion mass-spectrometry revealed the unintentional incorporation of In at a concentration equivalent to 1–2 monolayers. Here we introduce a new growth procedure—the sequential growth scheme where each section of the VECSEL is grown separately, and after the growth of a section, the sample is taken out of the growth chamber and stored in the buffer chamber while the group-III cell temperatures are adjusted. After the new group-III fluxes have been stabilized, the wafer is transferred back into the growth chamber and the next section of the laser is grown. This way the unintentional incorporation of In at interfaces between different sections of the VECSEL structure can be avoided. A comparison of nominally identical VECSEL structures grown within the same growth campaign using the two different growth procedures reveals an increase of the maximum output power of nearly 100% for a 2.0 μm emitting VECSEL structure grown with the sequential growth scheme accompanied by an improvement of the optical-to-optical power conversion efficiency from 14.4% to 21.5%.     

Kinetic Investigations within the Transition Region from Polyhedral to Skeletal Growth Mode (V). Growth Kinetics of the Pyramidal Face of Zinc Single Crystals under Diffusion Conditions

The growth kinetics of the pyramidal face of zinc single crystals is studied in the presence of argon. The curves size vs. time provide evidence that smaller crystals grow in a kinetic regime and after reaching a certain critical size their growth continues in a diffusion regime. The growth kinetics of faces {101 } and {0001} are compared. It is established that the growth of both faces simultaneously changes from a kinetic to a diffusion growth mode. During the transition between the two regimes, however, loss of the morphological stability only of the smooth {0001} face is observed, while the {101 } face with macro steps formed on the surface acquires a skeletal shape after prolonged growth. It is shown that the appearance of morphological instability depends on the surface structure of the crystal faces.     

Quantitative Description of the Influence of the Inhibitor Concentration on the Growth Rate of Barium Sulfate Crystals in Suspension (III)

To describe quantitatively the effect of a growth inhibitor on the growth rate of barium sulfate crystals, suspended in a supersaturated solution, the “strength of inhibition” has been introduced. The strength of inhibition is defined as the ratio of the mean linear growth rates without and with inhibitor at the same value of the growth affinity. It has been shown that the strength of inhibition, exerted by 1-hydroxyethylidene-1, 1-bisphosphonic acid (HEDP) and aminomethylene-bisphosphonic acid (AMDP) on the growth process, not only depends on its concentration, but also on the growth affinity, or probably even on both the growth affinity and the changes in the geometry of the crystals due to their growth in the presence of an inhibitor.     

A numerical study of convection during THM growth of CdTe with ACRT

The accelerated crucible rotation technique (ACRT) is an effective way to increase mixing in the solution zone in travelling heater method (THM) growth and to obtain higher growth rate limits. In this paper, detailed numerical calculations of the combined thermally driven and forced convection during THM growth of CdTe from a Te-rich solution are presented. The effects of various parameters of ACRT on the mixing are considered and a possible optimum cycle for high growth rate limits is given.     

Systematic study of epitaxy growth uniformity in a specific MOCVD reactor

Gallium nitride (GaN) is a direct bandgap semiconductor widely used in bright light‐emitting diodes (LEDs). Thin‐film GaN is grown by metal‐organic chemical vapour deposition (MOCVD) technique. Reliability, efficiency and durability of LEDs are influenced critically by the quality of GaN films. In this report, a systematic study has been performed to investigate and optimize the growth process. Fluid flow, heat transfer and chemical reactions are calculated for a specific close‐coupled showerhead (CCS) MOCVD reactor. Influences of reactor dimensions and growth parameters have been examined after introducing the new conceptions of growth uniformity and growth efficiency. It is found that GaN growth rate is mainly affected by the concentration of (CH3)3Ga:NH3 on the susceptor, while growth uniformity is mainly influenced by the recirculating flows above the susceptor caused by natural convection. Effect of gas inlet temperature and the susceptor temperature over the growth rate can be explained by two competing mechanisms. High growth efficiency can be achieved by optimizing the reactor design.     

Growth of cadmium zinc telluride by liquid phase electroepitaxy

This study was undertaken to examine the feasibility of growing CdZnTe by liquid phase electroepitaxy. Based on our successful LPEE system of GaInAs, a new crucible to grow CdZnTe was developed. The development presented numerous difficulties. The physical properties of CdZnTe make this material very difficult to grow. All components of the system were investigated. Electromigration of the solute across the solution carries species towards the growth interface. In liquid Cd‐Zn‐Te, the CdTe and ZnTe species remain associated, contrary to the GaInAs system. Experiments showed that LPEE growth of CdZnTe is possible and the electromigration mechanism functions well in the CdZnTe solution. Despite this, other problems remained with the new LPEE system. The preparation of the solution proved difficult without pressurizing the LPEE crucible. Control of the reaction required the use of pre‐compounded CdTe and ZnTe. Proper control of the solution saturation is imperative to ensure minimal dissolution of the seed prior to growth initiation and a reasonable growth rate during growth. The solution remained an issue during the duration of growth due to the high vapor pressures of the constituents. Tellurium evaporation during growth could lower solution volume until electrical contact across the solution is broken. Careful preparation of appropriate solution volume was imperative for successful growth. In LPEE, a uniform electric current passage across the growth interface is necessary for uniform and stable growth interface. This requires the design of a uniform contact zone between the bottom graphite electrode and the seed crystal. The contact zone issue was not adequately resolved in this study. However, a number of successful growth runs were achieved despite the electrical contact problems. Results show that the LPEE of growth CdZnTe is feasible. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

XeCl excimer laser assisted CBE growth of GaAs

The effect of 12 ns, 308 nm (XeCl) excimer laser pulses on the CBE growth rate of GaAs, at temperatures below the maximum non-laser assisted growth rate, G_max, has been studied as a function of laser fluence and repetition frequency. There is a threshold fluence for growth rate enhancement, above which the growth rate is dependent on repetition frequency, being restored to G_max at 20 Hz. The growth rate in the laser spot is measured by dynamic optical reflectivity (DOR).     

Growth mechanism of copper whiskers by the hydrogen reduction of cuprous iodide

A small quantity of cuprous iodide (less than 30 mg) was reduced by hydrogen at 650 or 700°C for various periods of time (15 sec to 4 min) and quenched to interrupt whisker growth. This was done in order to examine the nature of the growth of copper whiskers. Scanning electron microscopic observation and X-ray microanalysis revealed that almost all the whiskers quenched after the growth for 30 sec or less had cuprous iodide droplets at their tips and also the lateral surfaces were covered by thin cuprous iodide layers. The manner in which the copper crystals grow is similar to growth by the droplet mechanism or by the VLS mechanism in that the nutrient is supplied by a liquid drop on the tip of the whisker. Whiskers thicken during and after the growth in length. The whiskers quenched after the growth for 1 min or more had well-developed lateral surfaces and did not have the droplets at the tips. Preferential condensation and reduction were found to occur at the whisker edges. Based on the observed facts, a growth mechanism is presented. Secondary whisker growth on the whisker tips was also investigated.     

Analysis and calculation of the formation of grown-in microdefects in dislocation-free silicon single crystals

The physical model of the formation of grown-in microdefects in dislocation-free Si single crystals has been analyzed. The mathematical models used to describe the processes of defect formation in crystals during their growth are proven to be adequate to the physical model. A technique is proposed to determine and calculate the defect structure in dependence of the crystal growth conditions (growth technique, growth rate, temperature gradients, cooling rate). It is shown that the theoretical study of the real crystal structure in the dependence of the thermal growth conditions using an original virtual technique for analyzing and calculating the formation of grown-in microdefects is a new experimental technique.     

The origin of synthetic polycrystalline skeletal diamonds

A reaction vessel for diamond production modified by using a graphite heater around a metal-graphite sandwich set has changed the physical conditions (especially the thermal conditions) inside the set during the synthesis process. There has been built up a reduced radial temperature gradient, as compared to the gradient in a reaction vessel for repetition work. As an effect of the process polycrystals with very different shapes, morphology, and internal structure have been achieved, and they are named as skeletal polycrystals. Basing on the relation between crystal morphology and its growth conditions, in this paper a suggestion of this polycrystals' growth process is described. It is assumed that the principal driving force of polycrystals' growth process has been the supersaturation of the cobalt solution by graphite. As a result of diamond crystallization, the graphite content decreases and causes the change of growth mechanism from continuous growth through two-dimensional nucleation to spiral growth. It is well noticed in the skeletal polycrystals' morphology.