Te溶剂-Bridgman法Cd0.9Mn0.1Te晶体生长习性研究

采用Te溶剂-Bridgman法生长了尺寸为φ30 mm× 60 mm的Cd0.9Mn0.1Te:In晶锭,通过淬火得到了生长界面形貌.测试了晶片在近红外波段的透过率和电阻;采用化学腐蚀的方法观察了晶片中位错,Te夹杂和孪晶界;采用光学显微镜和红外成像显微镜观察了生长界面处附近的形貌.测试结果表明,晶锭中部结晶质量较好的晶片红外透过率达到60％,电阻率达到2.828×1011Ω · cm.位错密度在106 cm-2数量级,Te夹杂密度为1.9×104 cm-2,同时孪晶密度明显低于Bridgman法生长的晶锭.生长界面宏观形貌平整,呈现微凹界面.但由于淬火过程的快速生长,界面微观形貌发生变化,呈现不规则界面,并在界面附近形成富Te相的包裹.     

‘Star‐like’ defects in Cd‐annealed CdZnTe crystals—an experimental study of their origin and formation mechanism

We conducted low‐temperature annealing experiments at temperatures slightly above and below the melting point of Te to clarify the effects of the state of Te inclusions (solid or liquid) upon the formation of ‘star‐like’ defects in Cd‐annealed CdZnTe (CZT). We also carried out post‐growth annealing experiments with and without using Cd vapor to clarify the mechanism of formation of such defects. We demonstrated that these ‘star‐like’ defects are due to the reaction between in‐diffused Cd atoms and the molten Te inclusions, but we found no observable ‘one‐to‐one’ correlation between ‘star‐like’ defects and Te inclusions. The non‐uniform distribution of Te inclusions in the CZT matrix could account for this phenomenon since the punching distance of the dislocations depends on the volume fraction of inclusions within the matrix.     

Optical property analysis of CZT:In single crystals after annealing by a two-step method

Indium-doped Cd_1−xZn_xTe (CZT:In) single crystals were annealed by a two-step method, including a high-temperature step and a low-temperature step in sequence. IR transmittance spectrum, I–V curve and PL spectrum were used to characterize the CZT single crystals. After annealing, the opto-electrical properties of the CZT:In crystals were improved obviously. The average IR transmittance was remarkably increased by about 23%, and the resistivity was enhanced by as high as four orders of magnitude. In the PL spectra, the intensity of the (D⁰, X) peak prominently increased, and the full-width-at-half-maximum was reduced. Meanwhile, the intensity of the DAP peak decreased greatly, and the structure became practically indistinguishable from the background. Moreover, the intensity of the D_complex peak also decreased. The investigation shows that these improvements in the physical properties after annealing are due to variations in the micro-structures. The two-step annealing method can eliminate precipitates/inclusions, remove impurities, compensate Cd vacancies, decrease dislocations and reduce internal stress.     

Cd0.80Zn0.20Te晶体的生长及性能研究

用本实验室合成的Cd0.80Zn0.20Te多晶料为原料,采用改进的布里奇曼法在镀碳和未镀碳的石英安瓿中生长出Cd0.80Zn0.20Te晶锭。使用X射线衍射仪对合成产物及晶锭进行了分析,生长晶体的X射线衍射峰尖锐,摇摆谱对称,表明晶锭的结晶性能较好;用IRPrestige-21红外光谱仪分析了晶体的红外透射光谱,测试结果表明安瓿镀碳后生长的晶体位错密度小,均匀性较好,电阻率优于未镀碳安瓿生长的晶体;晶体的蚀坑密度在103~104cm-2之间,比未镀碳安瓿生长的晶体低1个数量级。     

Ca0．80Zn0．20Te晶体的生长及性能研究

用本实验室合成的Ca0．80Zn0．20Te多晶料为原料，采用改进的布里奇曼法在镀碳和未镀碳的石英安瓿中生长出Ca0．80Zn0．20Te晶锭。使用X射线衍射仪对合成产物及晶锭进行了分析，生长晶体的X射线衍射峰尖锐，摇摆谱对称，表明晶锭的结晶性能较好；用IRPrestige-21红外光谱仪分析了晶体的红外透射光谱，测试结果表明安瓿镀碳后生长的晶体位错密度小，均匀性较好，电阻率优于未镀碳安瓿生长的晶体；晶体的蚀坑密度在10^3-10^4cm^-2之间，比未镀碳安瓿生长的晶体低1个数量级。     

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.     

Vacancy defects in bulk ammonothermal GaN crystals

We have applied positron annihilation spectroscopy to study in-grown vacancy defects in bulk GaN crystals grown by the ammonothermal method. We observe a high concentration of Ga vacancy related defects in n-type samples in spite of the low growth temperature, suggesting that oxygen impurities promote the formation of vacancies also through other mechanisms than a mere reduction of thermodynamical formation enthalpy. On the other hand, no positron trapping at vacancy defects is observed in Mg-doped p-type samples, as expected when the Fermi level is close to the valence band and intrinsic defects are dominantly positively charged. Annealing of the samples at temperatures well above the growth temperature is found to change significantly the defect structure of the material.     

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)     

Floating zone growth and characterization of ruby single crystals

Large, high optical quality single crystals of ruby have been grown successfully by the floating zone method under air atmosphere. The size of the grown crystal is typically 60‐70 mm in length and 7‐8 mm in diameter. The obtained crystals were red and did not have any macroscopic defects such as cracks and inclusions. Grown crystals were characterized by powder X‐ray diffraction (XRD) methods, polarized optical microscopy, scanning electron microscopy (SEM). The absorption and fluorescence spectra were measured at room temperature and the dielectric constant measurements of ruby crystals were also presented. Defects occurring in single crystals of ruby during crystal growth by floating zone method are described, and their correlation with the growth parameters is discussed. The origin and control of these defects in grown crystals were studied and the optimum method was proposed. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and interface study of 2 in diameter CdZnTe by THM technique

Growth interface of large diameter CdZnTe ingots grown from Te solution by travelling heater method have been studied. Both macroscopic and microscopic investigations were carried out. The results indicated that the shape of the interface strongly governs the grain growth on the ingot, while the microscopic morphology of the growth interface is responsible for Te inclusions in the grown crystal.     

Compensation of CdTe by Doping With Gallium

Semi‐insulating CdTe single crystals doped with Ga were grown from the vapour phase by the modified Markov technique MMT. The study of the resistivity map in the cross‐sections cut a long the growth direction has been performed. The compensation phenomenon is analysed in the framework of the three levels Fermi‐statistic model. It is shown that a semi‐insulation behaviour throughout the ingot is due to the compensation of shallow impurities by the deep level. From the low ‐temperature photolum inescence spectra it was concluded that shallow donors (Ga_Cd) are partly compensated by (Ga_Cd‐V_Cd)^‐and (Ga_Cd‐Cd_Te) complexes and by residual acceptors (Na_Cd, Cu_Cd) . The microscopic structure of (Ga_Cd‐Cd_Te) complexis proposed based on the value of its local phonon mode and the growth conditions. A native defect like Te_Cd which has a deep level near the middle‐band‐gap is suppose to give a stable compensation and a tolerance for variation in shallow impurity concentrations.     

Phase-field simulations of Te-precipitate morphology and evolution kinetics in Te-rich CdTe crystals

Te precipitates are one of principal defects that form during cooling of melt-grown CdTe or CZT crystals when grown Te-rich. Many factors such as the kinetic properties of intrinsic point defects (vacancy, interstitial, and antisite defects); stresses associated with the lattice mismatch between precipitate and matrix; temperature gradients and extended defects (dislocations, twin and grain boundaries); non-stoichiometric composition; thermal treatment history all affect the formation and growth/dissolution of Te precipitates in CdTe. A good understanding of these effects on Te precipitate evolution kinetics is technically important in order to optimize material processing and obtain high-quality crystals. This research develops a phase-field model capable of investigating the evolution of coherent Te precipitates in a Te-rich CdTe crystal undergoing cooling from the melt. Cd vacancies and Te interstitials are assumed to be the dominant diffusing species in the system, which is in two-phase equilibrium (matrix CdTe and liquid Te inclusion) at high temperatures and three-phase equilibrium (matrix CdTe, Te precipitate, and void) at low temperatures. Using available thermodynamic and kinetic data from experimental phase diagrams and thermodynamic calculations, the effects of Te interstitial and Cd vacancy mobility, cooling rates and stresses on Te precipitate, and void evolution kinetics are investigated.     

Growth and characterization of tris allylthiourea mercuric chloride crystals

Single crystals of tris allylthiourea mercury chloride (ATMC), a semi‐organic nonlinear optical material, have been grown from a low‐temperature solution growth technique by slow cooling method. In the present work, we have grown ATMC crystal which is a new nonlinear optical material (NLO) having high optical quality and its second harmonic generation (SHG) efficiency is thrice that of Urea. The grown crystals have also been subjected to various characterization studies like X‐ray diffraction, UV‐VIS, FT‐IR and TGA‐DTA. X‐ray powder diffraction study confirmed the crystal structure of ATMC, UV‐VIS /FT‐IR spectral analysis showed the crystal has good optical transmission in the entire visible region and TGA‐DTA studies showed the thermal properties and complex degradation of ATMC crystal. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and morphology of the single crystals of thermoelectric oxide material NaxCoO2

We have grown single crystals of recently discovered thermoelectric oxide material Na_xCoO₂ using NaCl flux. Crystals of sizes upto 1.5 x 1.5 x 1.5 mm³ having different morphological habits were reproducibly grown. The atomic force microscopic studies show that along c‐axis crystals grow via 2D layer‐by‐layer mechanism. The X‐ray diffraction analyses show that grown crystals are rich in Na content as compared to the starting charge indicating that NaCl flux also acts as a source of Na. The resistivity of the crystals exhibited a linear temperature dependence in the region between 30 and 300 K. © 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim     

CdSe单晶体的生长及其特性研究

本文报道了用改进的垂直气相法(多级提纯垂直气相法)生长富Cd的CdSe单晶体,并对晶体的性能进行了观测,其电阻率为107Ωcm量级,电子陷阱浓度为108cm-3量级,第一次报道了(110)面的腐蚀形貌。结果表明：采用这种方法制备CdSe单晶,设备简单,易于操作,在提纯和生长过程中不需要转移原料,有利于减少晶体中的杂质含量,降低位错密度,改善晶体的电学性能。多级提纯垂直气相法是一种有前途的CdSe单晶体生长的新方法。     

Cd1−xZnxTe: Growth and characterization of crystals for X-ray and gamma-ray detectors

The choice a suitable crystal growth method and a reasonable x value is of profound importance in the preparation of high quality Cd_1−xZn_xTe crystals for x-ray and gamma-ray detectors. The present paper reviews the evolution and development of Cd_1−xZn_xTe crystal growth for x-ray and gamma-ray detectors. At the same time, emphasis is put upon finding the relationship between the x value and the quality of the Cd_1−xZn_xTe. Three sets of Cd_1−xZn_xTe ingots with different x values, specifically 0.10, 0.15, and 0.20 were grown by the vertical Bridgman method (VBM) and characterized. Their x specification was then correlated with their dislocation densities, Te precipitates, inclusions, IR transmission, resistivities, and impurity concentrations, respectively. It was found that VBM Cd_0.85Zn_0.15Te as grown in this paper possessed the best choice of qualities with respect to defects and impurities.     

Bridgman and Czochralski growth of Ge?Si alloy crystals

Ge_1–xSi_x crystals were grown with the Bridgman and the Czochralski method over a wide concentration range. With the Bridgman process single crystals up to 40 at.% Si were possible. The reasons for polycrystalline growth were the permanent contact of the interface with the crucible wall in combination with curvature towards the crystal and inclusions of high Si concentration. Analysis of striations in Czochralski grown material showed that in this process the crystal does not continuously grow in one direction but consists of piece-wise grown crystals in which the composition permanently changes. According to that fact the main reason for polycrystalline growth in the Czochralski process is common due to lattice mismatch between the seed and equilibrium concentration transients in the crystal corresponding to the microscopic growth rates.     

Nucleation kinetics and growth of nonlinear optical bis (dimethyl sulfoxide) manganese mercury thiocyanate single crystals

Nonlinear optical (NLO) material of bis (dimethyl sulfoxide) manganese mercury thiocyanate (MMTD) was synthesized by two step reaction method. The solubility and metastable zonewidth were experimentally determined in order to optimize the growth parameters. Bulk crystals of MMTD were grown by slow cooling and slow evaporation methods. The structure of the grown crystal was confirmed by X‐ray diffraction analysis. Presence of functional groups and the coordination of Lewis base ligand of dimethyl sulfoxide (DMSO) were confirmed by FT‐IR analysis. Optical transparency of the grown crystals was studied by UV‐Vis spectroscopy. Nonlinear optical property of the grown crystal was confirmed by Kurtz powder method. Etching studies reveal the formation of triangular hillock etch patterns, indicative of 2D nucleation mechanism. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and etching of anhydrous diglycine sulfate single crystals

Single crystals of anhydrous diglycine sulfate are grown at constant temperature by evaporation method. The crystals are grown at various temperatures and their growth rate is determined. A chemical etchant for dislocation studies is reported. The perfection of the crystals grown at various temperatures has been studied using etching technique. It is found that the crystals contained inclusions of the mother liquid. The crystals grown below 28° are almost free of inclusions and the dislocation density is also low.     

Studies on the growth and defects of La3Ga5SiO14 (LGS) crystals

New and high quality piezoelectric crystals La₃Ga₅SiO₁₄ (LGS) grown by the Czochralski method in a Platinum or Iridium crucible are reported in this paper. The growth defects in the LGS crystals were investigated by Transmission electron microscopy (TEM). It was found that cracks, inclusions, grain boundary and thermal stress in the LGS crystals. Their formation mechanisms and the method of eliminating these defects are discussed. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)