Growth and characterization of semiconducting cadmium selenide thin films

Semiconducting thin films of cadmium selenide have been grown by conventional thermal evaporation technique. The effect of various growth parameters like rate of deposition and deposition temperature has been studied in detail. Films deposited at room temperature are cadmium rich with segregated selenium globules. A deposition temperature of 453 K has been found to yield stoichiometric, homogeneous films. The films have been analysed for optical band gap and thermal activation energies. Films of low electrical resistivity have been obtained for possible applications.     

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)     

Metalorganic vapour phase epitaxy of mercury cadmium telluride

The present review covers the fundamental factors involved in the the metalorganic vapour phase epitaxy of mercury cadmium telluride. In addition recent significant developments which could have an important influence on the future of the technology are discussed. The topics covering these developments include growth techniques, photoepitaxy, in-situ monitoring, “new” precursors, substrates and layer quality. The review highlights the advanced nature of the technology, which inspite of currently-addressed limitations has an important future.     

Atomic force microscopy studies on liquid inclusions and induced defects of cadmium mercury thiocyanate crystal

Liquid inclusions and various defects accordingly induced on a nonlinear optical material of CMTC crystal were investigated by atomic force microscopy. Liquid inclusions are chiefly caused by formation of macrosteps, which result from impurity‐induced inhibiting of step growth and meeting of step trains advancing along different directions. Liquid inclusions induce generation of dislocations and even cracks within the crystal by three‐dimensional nucleation growth. Liquid inclusions also provide screw dislocation growth sources, leading to formation of spiral hillock trains with ridged tails. Etching experiments reveal circular hollow cores, indicative of screw dislocation growth, and negative crystals resulting from further crystallization in the liquid inclusions. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Study of crystalline perfection and thermal analysis of zinc cadmium thiocyanate single crystals grown in silica gel

Zinc cadmium thiocyanate ZnCd(SCN)₄ abbreviated as ZCTC is a bimetallic thiocyanate complex that exhibits excellent nonlinear optical property. Single crystals of ZCTC have been grown in silica gel by the process of diffusion. Colorless transparent crystals of size 12 mm x 2 mm x 1.3 mm have been obtained. High resolution X‐ray diffraction study was carried out to investigate the crystalline perfection of the grown crystal and the quality of the crystal was found to be quite good. Thermal stability of the grown crystal was investigated by thermogravimetric and differential thermal analyses. Fourier Transform Infrared spectrum was recorded to confirm the functional groups. Microhardness of the crystal is also studied. Being a nonlinear optical material, a comparative study of its second harmonic generation efficiency with urea has been made. (© 2007 WILEY ‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

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.     

Growth and characterization of cadmium magnesium tetra thiocyanate crystals

Cadmium Magnesium Tetra Thiocyanate, CdMg(SCN)₄, [CMTC] belongs to bimetallic thiocyanate complexes. CMTC crystals has been grown by solution growth technique at room temperature. The morphologies of the grown crystals are identified by single crystal analysis. Also the Powder X‐ray Diffractogram of the crystal has been recorded and the various planes of reflection are identified. The title compound crystallizes under triclinic structure with lattice parameters a = 10.0976 Å, b = 7.5015 Å, c = 5.7720 Å and β = 90.2135°. The presence of magnesium and cadmium in the grown crystals were confirmed through Atomic Absorption Spectroscopy. The grown crystals are analysed qualitatively by Fourier Transform Infrared (FTIR) and Fourier Transform Raman spectral measurements. The transmittance spectrum of the crystal in the UV‐Visible region has been recorded and analysed. The dielectric measurements for the crystals were carried out in the microwave region. The thermal stabilities of the crystals were studied by using different thermal analyses like Thermo Gravimetric Analysis (TGA), Differential Thermal Analysis (DTA) and Differential Scanning Calorimetry (DSC). (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and defect studies of CdTe particles

The paper reports the epitaxial growth of cadmium telluride (CdTe) particles by thermal deposition on cleaved planes of (001)NaCl and (001)KBr. Using high resolution transmission electron microscopy and electron diffraction it was shown that CdTe particles could have different orientation and phase (cubic or hexagonal) depending on the substrate temperature. Their most common defects are twins and stacking faults.     

Growth kinetics of zinc(tris)thiourea sulphate (ZTS) crystals

Growth kinetics of zinc (tris) thiourea sulphate (ZTS) crystals investigated as a function of supersaturation is reported in this communication. Crystal growth rates were investigated normal to the (100), (010) and (001) faces under growth conditions employed for bulk crystal growth. The growth rates normal to (010) and (100) were found to follow the continuous growth model (R_G = Cσ) with respect to the supersaturation whereas the growth rates normal to (001) was found to satisfy birth and spread (B+S) model (R_G = Aσ^5/6 exp(‐B/σ)). The growth rates observed normal to the studied face are in agreement with the growth mechanism predicted from the estimated α (Jackson) factor. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of glycine doped bis thiourea cadmium chloride single crystal

Single crystal of 2 mol% glycine doped Bis Thiourea Cadmium Chloride, a semi organic nonlinear optical material has been grown by slow evaporation technique. Good quality single crystal with dimension 14 × 12 × 5 mm³ was harvested after 35 days. The influence of amino acid glycine was studied for 1, 2 and 3 mol% glycine doped Bis Thiourea Cadmium Chloride by Kurtz and Perry powder second harmonic generation test and compared with pure Bis Thiourea Cadmium Chloride which confirms the enhancement of second harmonic generation property of glycine doped Bis Thiourea Cadmium Chloride. The large enhancement was found for 2 mol% glycine doping. The grown crystal was characterized by various characterizations viz. single crystal X‐ray diffraction, energy dispersive X‐ray (EDAX), Fourier Transform Infrared Spectroscopy (FTIR) analysis, UV‐visible absorption, thermo gravimetric analysis (TGA). (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of nonlinear optical zinc hydrogen phosphate single crystal grown in silica gel

Good optical quality single crystals of zinc hydrogen phosphate (ZnHPO₄) having dimensions up to 8×2×2 mm³ have been grown with the aid of sodium meta silicate gel. Single crystal XRD studies confirm that the crystal belongs to the orthorhombic system with space group P2₁2₁2₁. The functional groups present in the crystals were confirmed using FTIR technique. Optical absorbance shows very low absorption in the entire visible region. Differential thermal and thermo gravimetric analysis confirmed that the crystal is stable up to 193°C. Photoconductivity study reveals positive photoconductivity in the presence of photo active centers formed by trap energy levels. The NLO activity of the crystal was confirmed by Kurtz powder technique. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

提拉法制备铜单晶研究

采用提拉法生长出大尺寸(111)铜单晶,晶体尺寸为ф(12～19)mm×85 mm.通过XRD、金相显微分析讨论了铜单晶的晶体结构与生长缺陷,并采用双臂电桥测定(111)铜单晶的电阻率.结果表明:晶体具有(111)取向、强度高,表明晶体取向良好;蚀坑呈典型三角锥形,位错密度在105～106 cm-2之间;在室温下,(111)铜单晶电阻率为1.289×10-8Ω·m.     

助熔剂法生长ZnO晶体

采用Bi4B2O9、CdB2O4和BaB2O4为助熔剂,获得了毫米级的氧化锌单晶.Muiliken的电负性理论和Viting的平均轨道电负性提供了一个选择晶体生长所采用的助熔剂的有效方法.实验结果表明ZnO晶体的生长温度比文献报道的均低,从而有效地减少了ZnO以及助熔剂的挥发.本文给出了几种有望获得大尺寸ZnO单晶的助熔剂.     

溶液法五氯硝基苯单晶生长的研究

测定PCNB在丙酮溶剂中的溶解度,采用恒温溶剂蒸发法首次在丙酮中成功生长出PCNB单晶.结果显示:302 K以下温区具有较小的温度系数,适用于恒温蒸发法生长单晶;生长出了厘米尺寸的PCNB晶体;红外和拉曼光谱的测量结果说明所生长的晶体中未包裹溶剂;X射线衍射分析表明,所生长出晶体结构为六方晶系,单晶质量较好.     

反式二苯乙烯(TSB)的溶液法晶体生长

本文观测了TSB在苯甲醚等有机溶剂中的结晶习性,测定了相应的溶解度曲线和亚稳区.采用溶液降温法在50~30 ℃的温度范围内进行晶体生长,获得透明度好的厘米级TSB晶体.通过对所得晶体进行X射线粉末衍射、紫外-近红外透过光谱、吸收光谱和紫外荧光光谱等测试,表明:本实验使用的不同生长溶剂对TSB晶体结构不会产生影响,所得晶体在410~1000 nm波长范围内透过率不低于80;,而在200~360 nm范围内有吸收,在波长为272.8 nm的激发光作用下,得到较强的荧光峰,峰位为386 nm.     

LiNbO3晶体的坩埚下降法生长

通过选择合适的原料配比(Li2O 48.6mol;,Nb2O5 51.4mol;),控制固液界面处的温度梯度为20～40℃/cm,晶体生长速度为0.6～1.5mm/h,采用密闭条件下的坩埚下降法工艺成功地生长出了具有良好光学均匀性的完整LiNbO3单晶.用X射线粉末衍射表征获得的LiNbO3晶相,讨论了若干工艺条件对晶体组分与质量的影响.测定了未密闭条件下生长的LiNbO3晶体不同部位样品的紫外可见光谱,发现其吸收边沿生长方向发生红移,并讨论了产生此现象的原因.     

熔盐提拉法生长大尺寸KGW晶体及其拉曼特性研究

β-KGd(WO4)2(简称KGW)晶体是一种兼具激光基质和拉曼性能的优秀材料,受到了广泛的关注和研究.采用熔盐提拉法生长了尺寸>60 mm、质量>800 g的KGW晶体,光学均匀性为1.34×10-5.在生长的晶体中,观察到了包裹体聚集层、空洞和开裂等较大尺寸缺陷,并探讨了原因.初步的激光实验实现了1151.3 nm拉曼激光输出,功率80 mW,拉曼频移为898.2 cm-1.     

导模法生长六片片状蓝宝石晶体的研究

采用导模法生长出六片片状蓝宝石晶体,单片尺寸为350 mm×80 mm×2 mm.通过CGSim模拟软件模拟计算和实验验证,确定了合适的生长温场为横向温梯2.9~4.6 K/mm,生长速度控制在5~10 mm/h之间.对晶体进行双晶摇摆曲线测试,峰强度很高且对称性良好,摇摆曲线的半高宽FWHM=16.946″,证明晶体的结晶完整性很高.采用化学腐蚀法对六片晶体进行位错密度的检测,计算出晶体的位错密度都在103量级,中间晶体位错密度小于两边晶体的位错密度.测试了六片晶体的弯曲强度,最高强度达1583 MPa,中间晶体强度大于两边.     

结晶生长的化学键合理论

针对一般晶体的生长过程,在测定相应溶液(熔体)组成结构的基础上,我们引入了晶体生长过渡相区的概念,并采用键价模型来衡量生长过程中发生变化的化学键的键强度。过饱和溶液(熔体)中的生长单元经过生长过渡相区时,依据彼此之间弱的化学键合作用来微调其内部强的化学键,并以单个生长单元或者生长单元的简单连接体的形式键合进入晶格。在整个结晶生长过程中,生长单元之间弱的键合作用对整个结晶过程(生长速度、晶相的形成)起着决定性作用;同时,中等强度的化学键在生长过渡相区中的变化情况对晶体的最终形貌具有重要影响。     

Growth of Nd:Sr3Ga2Ge4O14 crystals by a modified Bridgman method

Bridgman growth of Nd:SGG (Sr₃Ga₂Ge₄O₁₄) crystals has been investigated for the first time. Pt crucible of ∅︁25mm×250mm with a seed well of ∅︁10mm×80 mm is used, and seed is SGG crystal of ∅︁10mm×50mm grown by Bridgman method in advance. The growth parameters are optimized as the furnace temperature is set to 1450∼1500°C, temperature gradient in the crystal‐melt interface is less than 25 K/cm and growth rate is less than 0.5mm/h. The Nd:SGG crystals with 25mm in diameter and 60mm in length are grown successfully from 1.5 to 8at% Nd³⁺ doped stoichiometric Sr₃Ga₂Ge₄O₁₄ melt. The distribution coefficient and concentration of Nd³⁺ in Nd:SGG crystals are obviously higher than those of Nd:YAG crystal. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)