Cd0.96Zn0.04Te单晶生长及晶体成分偏析

采用常规Ｂｒｉｄｇｍａｎ法和ＡＣＲＴ－Ｂ法进行Ｃｄ０．９６Ｚｎ０．０４Ｔｅ晶体生长实验。结果表明：ＡＣＲＴ产生的强迫对流在很大程度上消除了侧壁形核，有利于获得大的晶体；ＡＣＲＴ的加入提高了有效分凝系数ｋｅｆｆ，使其向平衡分凝系数ｋｅｑ趋近，导致轴向的偏析增大。     

Effect of growth conditions on the compositional homogeneity of Cd<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te crystals

A crystal growth unit has been designed for Cd_{1 − x} Zn _x Te growth by the axial-heat-flux-close-to-the-phase-interface (AHP) method at argon overpressures of up to 12 MPa. The influence of melt superheating, growth rate, melt layer thickness, argon pressure, and growth mode on the Zn distribution in 21- to 45-mm-diameter crystals and defect formation in Cd_{1 − x} Zn _x Te ingots has been investigated. The results demonstrate that the AHP method offers the possibility of effectively controlling the shape of the solid-liquid interface and ensures low fluid velocity and high radial compositional homogeneity. The feeding method used markedly improves the axial Zn profile and ensures low dislocation density (5 × 10³ cm⁻²) in the grown crystal.     

Investigation of effect of constitutional supercooling and solute segregation in CZT-LPVB with finite element analysis method

Crystal growth of Cd_0.9Zn_0.1Te (CZT) using the Liquid-phase Vertical Bridgman method (LPVB) is numerically simulated and analyzed using the simulation software of Comsol Mutiphysics. The influence of curvature on the solid-liquid interface is studied, and the radial solute segregation is calculated for three kinds of growth method. The energy dispersive X-ray (EDX) detector of an SEM was used to test the concentration of Zinc. And all the calculated data are in agreement with the results of the experiments numerically. The diffusion transported mechanism during supercooling of CZT crystal growth was studied and the freezing point curve and the thickness of the boundary layer for different values of G (temperature gradient) and v (growing rate) are discussed.     

Two-step growth of Cd0.96Zn0.04Te/Si(111) epilayers by HWE

High quality Cd_1−xZn_xTe, x = 0.04 epilayers are successfully grown directly on hydrogen-terminated Si(111) substrates by hot wall epitaxy method. Growth conditions are optimized in order to grow single crystal films with desired composition. It is found that surface morphology of the epilayers is dramatically affected by the growth temperature and the growth rate at the early stage of the crystal growth. Applying limited high substrate temperature of T_sub = 440 °C and low growth rate of 0.04 μm/h, the crystallinity is significantly improved and for the first time a pseudomorphic 2D growth is observed notwithstanding of the large lattice mismatch. Designing a suitable two-step growth process makes it possible that Cd_1−xZn_xTe/Si(111), x = 0.04 epilayers are fabricated with good surface morphology, which could be used as lattice matched substrates for MCT and MCZT epitaxy.     

Growth and characterization of Hg1-xCdxTe epitaxial films by isothermal vapour phase epitaxy (ISOVPE)

Growth of Hg_1-xCd_xTe epitaxial films by a new technique called asymmetric vapour phase epitaxy (ASVPE) has been carried out on CdTe and CZT substrates. The critical problems faced in normal vapour phase epitaxy technique like poor surface morphology, composition gradient and dislocation multiplication have been successfully solved. The epitaxial films have been electrically characterized by using the Hall effect and capacitance-voltage (C-V) measurements.     

Studies on polycrystalline Cd0.96Zn0.04Te thin films prepared by vacuum evaporation

Polycrystalline Cd_0.96Zn_0.04Te thin films are deposited onto glass substrates (Corning 7059) kept at room temperature by vacuum evaporation. The films exhibit zinc blende structure with predominant (1 1 1) orientation. The rms roughness of the films evaluated by atomic force microscope is 3.7 nm. The band gap energy of the films measured by optical transmittance measurement is 1.539 eV. The photoluminescence (PL) spectrum of the films shows intense emission due to free and bound exciton recombination and no emission associated with crystal imperfection and PL line shapes give indications of the high quality of the layers. These films have been implanted with properly mass analyzed Boron ions (¹⁰B⁺) and the effect of implantation has been analyzed by X-ray diffraction, Raman scattering and optical transmittance measurements and the results are explained on the basis of the implantation induced surface roughness and lattice disorder.     

Sputtering deposited ternary Zn1−xCdxO crystal films on Si(111) substrates

Using the d.c. reactive magnetron sputtering method we have successfully deposited completely (002)-oriented ternary Zn_1−xCd_xO (0≤x≤0.6) alloy crystal films without Cd segregation on Si(111) substrates. X-Ray photoelectron spectroscopy measurements show that Cd/Zn ratios in the films are nearly consistent with those in the targets. The Zn and Cd exist only in oxidized states, no evidence of metallic Zn or Cd was observed. The O/(Cd+Zn) atomic ratios of the films are in the range of 0.89-0.98. Transmission electron microscopy measurements show that for the (002)-oriented films the grains are columnar structures with the c-axis perpendicular to the Si substrate. By post-annealing treatments in O₂ ambient, the crystal quality of the Zn_1−xCd_xO films can be improved. For the sample of x=0.2, the optimal annealing temperature is 500 °C.     

Determination of optical constants of Cd1−xZnxTe thin films by spectroscopic ellipsometry

The optical response of vacuum-evaporated Cd_1−xZn_xTe thin films in the 1.5-5.6 eV photon energy range at room temperature has been studied by spectroscopic ellipsometry. The films of Cd_1−xZn_xTe (x=0.04) were deposited at room temperature onto well-cleaned glass substrates of film thickness 450 nm. The measured dielectric-function spectra reveal distinct structures at energies of the E₁, E₁+Δ₁ and E₂ critical points corresponding to the interband transitions. Dielectric related optical constants such as complex refractive index, the absorption coefficients and the normal incidence reflectivity, are presented. Results are in satisfactory agreement with the calculations over the entire range of the photon energies.     

Growth and properties of CdxHg1−xTe crystals

It has been found that there are two main factors complicating the preparation of Cd_xHg_1–xTe. The marked difference between the liquidus and solidus curves of the CdTe-HgTe pseudo-binary system gives the expected problems of segregation of CdTe with respect to HgTe during growth but there are also problems due to the segregation of any excess Te in the melt. A 2% excess of Te can give rise to pronounced constitutional supercooling effects. To avoid this, careful control of melt stoichiometry is required. This is made difficult by the high vapour pressure of mercury over the melt, the value of which is not known with great accuracy.The conditions of melt stoichiometry required for crystal growth do not necessarily give material of the required type and resistivity and this must be adjusted after growth by annealing at a controlled mercury pressure at a fixed temperature.     

Conductivity compensation in CdZnTe: Cl crystals with variable zinc content

The effect of cadmium vapor pressure during postgrowth annealing on the compensation of conductivity has been studied in semi-insulating Cd_1?x Zn _x Te:Cl crystals with variable zinc content (x = 0.005, 0.01, and 0.05), which are used in nuclear radiation detectors. At a small zinc content (x = 0.005 and 0.01), the main role in the in Cd_1?x Zn _x Te:Cl crystals is played by the cadmium point defects. In crystals with a higher zinc content (x = 0.05), the compensation of charged defects is incompletely controlled by changing the cadmium vapor pressure, which is evidence of a significant influence of the zinc point defects.     

Optical constants of vacuum-evaporated Cd0.96Zn0.04Te thin films measured by spectroscopic ellipsometry

The pseudodielectric-function spectra, (E)=₁(E)+i₂(E), of polycrystalline Cd_0.96Zn_0.04Te thin films in the 1.3–5.5 eV photon energy range at room temperature were obtained using spectroscopic ellipsometry. The measured dielectric-function spectra reveal that distinct structures at energies of the E₁, E₁+₁, and E₂ critical points are due to interband transitions. The Cd_0.96Zn_0.04Te thin films investigated were deposited by vacuum evaporation under a pressure better than 1.3×10^–3 Pa onto well-cleaned glass substrates kept at 300 K. The films exhibited zinc blende structure with predominant (1 1 1) orientation. The root mean square (r.m.s.) roughness of the vacuum-evaporated Cd_0.96Zn_0.04Te thin films evaluated by ex situ atomic force microscopy is 3.7 nm. Dielectric-related optical constants, such as the refractive index (n), extinction coefficient (k), absorption coefficient () and normal incidence of reflectivity (R) determined from the spectroscopic ellipsometry data are presented and analyzed. The optical constants of the films were also determined using optical transmittance measurements and the results are discussed.     

Growth and characterization of non-linear optical crystal Cd3Zn3B4O12

Cd₃Zn₃B₄O₁₂ polycrystals were synthesized by solid-state and wet chemical reaction methods. Cd₃Zn₃B₄O₁₂ single crystals with millimeter grade were grown from the self-flux B₂O₃ (Cd:Zn:B = 1:1:1.5); and larger crystals were obtained from the PbO-0.85PbF₂ fluxes easily. As-grown crystals were characterized by differential scanning calorimetry and thermogravimetric, X-ray diffraction, infrared and Raman spectral analysis, respectively. The non-linear optical coefficient of the Cd₃Zn₃B₄O₁₂ crystal is 2.6 times as large as that of KH₂PO₄ crystal. Chemical etching shows that this crystal is very stable in neutral solution and not hygroscopic in air at room temperature.     

Effect of the Cd<Subscript>0.96</Subscript>Zn<Subscript>0.04</Subscript>Te substrate polishing procedure on Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Hg<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Te liquid phase epitaxy

This paper examines the effect of polishing procedure on the surface quality of Cd_0.96Zn_0.04Te substrates for Cd _x Hg_{1 − x} Te liquid phase epitaxy. Two polishing procedures are tested: stepwise polishing involving abrasive, chemomechanical, and chemical steps with the use of various abrasives, and abrasive-free polishing. The optimal procedure is chemomechanical polishing with no abrasives. The type of substrate surface can be identified using the Nakagawa etchant, which produces etch patterns in the form of triangles on the A(111) surface and circles on the B(111) surface.     

Effect of annealing on semi-insulating CdZnTe:Cl crystals with variable zinc content

Semi-insulating Cd_1?x Zn _x Te:C1 crystals with variable zinc content (x = 0.0002, 0.005, 0.01, and 0.1) were grown using the method of horizontal directional solidification. The effect of the conditions of post-growth annealing under controlled cadmium vapor pressure and additional low-temperature annealing on the main parameters responsible for the quality of nuclear radiation detectors based on such crystals were studied.     

Antireflection properties of diamond-like carbon films on Cd<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te (<Emphasis Type="Italic">x</Emphasis> ∼ 0.04) single crystals

The optical properties of diamond-like carbon (DLC) films obtained by plasmachemical deposition on Cd_{1 − x} Zn _x Te (x ∼ 0.04) single crystals have been studied by ellipsometry. The ellipsometric data have been interpreted within the framework of a three-layer model of the DLC film-semiconductor crystal refractory system with transition layers between the film and substrate. It is found that DLC films exhibit antireflection properties in this refractory system in the IR spectral range. It is established that the proposed antireflection film-substrate structure is stable with respect to thermal cycling and ultrasonic treatment.     

Synthesis and nano-field-effect transistors of p-type Zn0.3Cd0.7Te nanoribbons

Ternarysemiconductor Zn_0.3Cd_0.7Te nanoribbons are, firstly, synthesized via a two-step process, and the structure characterizations reveal that the as-synthesized nanoribbons are single-crystalline with a zinc blende structure and a crystal growth direction of [1-10]. Nano-field-effect transistors are fabricated based on single nanoribbon, and the electron transport characteristics demonstrate that the Zn_0.3Cd_0.7Te ribbons have p-type conductivity with a mobility (μ_h) of 5.7 cm²V⁻¹S⁻¹ and carrier concentration (n_h) about 1.1 × 10¹⁷ cm⁻³. The prepared nanoribbons with significant p-type conductivity will be a very attractive candidate for nanoelectronic devices.     

Observation of curious spiral growth features in Tl doped Hg bearing high temperature superconducting tapes

Synthesis of Hg(Tl)Ba ₂ Ca ₂ Cu ₃ O _8+δ superconducting tapes have been accomplished by annealing the precursor tape, Ba ₂ Ca ₂ Cu ₃ O _y (fabricated by doctor blade tape casting technique) in an environment of Hg(Tl) vapour. Characterization of superconducting HTSC tape sample was carried out through XRD, TEM, SEM and R-T measurements. Surface morphological investigations of the as-synthesized Hg(Tl)Ba ₂ Ca ₂ Cu ₃ O _8+δ HTSC tapes by scanning electron microscope have shown the occurrence of curious growth characteristics resembling spiral like features. These growth spirals encompass nearly the whole grain suggesting that spiral growth led to the formation of small crystal like grains of superconducting material Hg(Tl)Ba ₂ Ca ₂ Cu ₂ O _8+δ .The likely mechanism for the generation of these screw dislocations has been elucidated in terms of incoherent coalescence of growth fronts formed from Hg(Tl):1223 and Hg(Tl):1234 nuclei.     

TeCd antistructural defects in CdTe crystals

Two-temperature annealing with a controlled vapor pressure of tellurium P _Te2 is used to study CdTe〈Cl〉 crystals under conditions of high-temperature thermodynamic equilibrium of the crystal with the gas phase (735–940 °C). For low pressures P _Te2 (≥P _min) Cl_Te+ begins to condense because of the formation of V_Cd ⁻² in the crystal. As P _Te2 increases, this mechanism of exact self-compensation no longer operates because of the formation of Te_Cd+ intrinsic antistructural point defects. Pis’ma Zh. Tekh. Fiz. 23, 30–34 (February 26, 1997)     

Effect of annealing temperature on the structural-microstructural and electrical characteristics of thallium bearing HTSC films prepared by chemical spray pyrolysis technique

In order to get good quality reproducible films of Tl : HTSC system, we have studied the different annealing conditions to finally achieve the optimized annealing condition. In the present investigation, Tl-Ca-Ba-Cu-O superconducting films have been prepared on YSZ (100) and MgO (100) single crystal substrates via precursor route followed by thallination. The post deposition heat treatments of the precursor films were carried out for various annealing temperatures (870°C, 890°C) and durations (1 and 2 min). The optimized thallination procedure occurred at 870°C for 2 min into good quality films withT _c (R = 0) ∼ 103 K for YSZ andT _c (R = 0) ∼ 98 K for MgO substrates, respectively. Further we have correlated the structural/microstructural characteristics of the films.     

Growth and characterization of gel grown pure and mixed iron-manganese levo-tartrate crystals

Several applications of iron tartrate and manganese tartrate compounds are reported in the literature. In the present investigation, we have grown pure and mixed iron (II)-manganese levo-tartrate crystals by single diffusion gel growth technique. Crystals with spherulitic morphology were harvested. The colouration of the crystals changed from black to pinkish brown upon increasing the content of manganese in the crystals. The crystals were characterized by FTIR spectroscopy, powder XRD, TGA, VSM and dielectric study. Crystal structures of different mixed crystals were studied. From TGA it was observed that on heating the hydrated crystals became anhydrous and then converted into oxides. Paramagnetic nature of the crystals was revealed from VSM study. The variation of the dielectric constant with frequency was studied. The results are discussed.