HgCdTe晶体ACRT-B法生长过程的分凝特性研究

在定量估算的基础上，明确了Ｈｇ１－ｘＣｄｘＴｅ晶体ＡＣ－ＲＴ－Ｂ法生长过程轴向溶质再分配的 经条件，导出了计算公式。以ＨｇＴｅ－ＣｄＴｅ伪二元相图为基础进行了计算表明，按照远红外控制器要求的成分配料（ｘ０＝０．２２），仅在晶锭的某一部分可获得符合成分容差的晶体，而采用其它相近的成分配比也能获得符合成分要求的晶体，采用ｘ０值更小的槽糕成分获得的满足成分要求的晶段更长，并且位于结晶质量较高的晶锭前段‘     

Cd0.8Mn0.2Te晶体的磁化强度和法拉第效应研究

采用垂直Bridgroan法制备出了x=0.2的Cd1-xMnxTe晶体(Cd0.8Mn0.2 Te).利用MPMS-7(magnetic property measurement system)型超导量子磁强计测量了Cd0.8Mn0.2Te晶体的磁化强度(M)与磁场强度(H)和温度(T)的关系,磁场强度范围为-159...     

CdTe单晶生长过程的分凝特性及其生长条件的选择

在Ｃｄ－Ｔｅ相图的基础出ＣｄＴｅ－Ｃｄ相图并定义其主要参数，讨论了高Ｃｄ的ＣｄＴｅ液体在结晶过程中的分凝特性及其生长条件对昌体中Ｔｅ固溶量的影响，进而维持平面生长界面所需的最小温度梯度。     

Bridgman法生长的MnxCd1-xIn2Te4晶体相形成规律和物理性能研究

采用Bridgman法生长了x为0.1,0.22和0.4的四元稀磁半导体化合物Mn_xCd_1-xIn₂Te₄晶体.研究了三根晶体中相的形貌、结构、成分和Mn_0.1Cd_0.9In₂Te₄晶体中各组元沿轴向和径向的成分分布.晶体生长初始端的组织为α+β+β₁,随着生长的进行,形成β相的单相区.在晶锭末端,形成In₂Te₃类面心立方结构化合物.组分x增大后,Mn_xCd_1-xIn₂Te₄晶体的吸收边向短波方向移动,禁带宽度则线性增大.磁化率测量结果表明:晶体在高温区的x^-1-T曲线服从居里-外斯定律,在低温区(<50K)则表现出顺磁增强现象.     

ACRT—B法晶体生长过程的传质模型

基于对ＡＣＲＴ－Ｂ法晶体生长对时流及传质特性的认识，提出了ＡＣＲＴ－Ｂ法晶体生长过程的一维传质模型。得到了包括初始过渡区、稳态区及终端过渡区轴向成分分布的解析解。定量计算结果表明，与传统Ｂｒｉｄｇｍａｎ法相比，在生长参数不变的条件下，运用ＡＣＲＴ会失去部分轴向面分均匀区。在保护ＡＣＲＴ提高结晶及径向成分均匀性的前提下，适当提高生长速度，选择尽可能小的坩埚最大转速△ωｍａｘ或选用长径比更大的坩埚，是     

Cd0.9Mn0.1Te晶体生长及其缺陷分析

采用Bridgman法和ACRT-B法生长了两根Cd0.9Mn0.1Te晶锭(简称CMT-B和CMT-A).采用光学金相显微镜和扫描电镜研究了这两种方法生长的晶体中出现的各种缺陷,并分析了其形成机理.采用JEOL-733电子探针测定了两根晶锭中Mn的分布.对比CMT-B和CMT-A两根晶锭,发现ACRT所产生的对流可提高Cd0.9Mn0.1Te晶体的结晶质量.     

温度梯度溶液生长法制备x=0.2的Cd1-xZnxTe晶体及性能研究

利用温度梯度溶液生长法(TGSG)在较低生长温度下制备了掺Al和掺In的x=0.2的Cd1-xZnxTe晶体,晶体起始生长温度约为1223K,温度梯度为20～30K/cm,坩埚的下降速度为1mm/h。采用红外显微镜、傅里叶红外光谱仪、扫描电镜能谱仪(SEM/EDS)和I-V测试分别研究了晶体中的Te夹杂相、红外透过率、Zn组分分布和电阻率。结果显示CdZnTe晶锭初始生长区、稳定生长区的Te夹杂相密度分别为8.3×103、9.2×103/cm-2,比垂直布里奇曼法生长的晶体低约1个数量级,红外透过率分别为61%、60%。Al掺杂CdZnTe晶体的电阻率为1.05×106Ω.cm,而In掺杂CdZnTe晶体的电阻率为7.85×109Ω.cm。晶锭初始生长区和稳定生长区的Zn组分径向分布均匀。     

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。     

Convection during the vertical Bridgman growth of Hg1−xCdxTe

Two different structures, obtained with specific growth parameters, in Hg_1–x Cd _x Te single crystals synthesized by the vertical Bridgman technique, are shown. A structure (small vertical line-shaped defects) located in the central part of the charge along the growth axis can be ascribed to convection induced by melt–solid interface curvature. The other structure, obtained in the first-to-freeze region of the ingot, when the temperature of the cold zone of the furnace is constant and a few degrees lower than the solidification one, can be ascribed to the convection rolls frozen in the solid matrix.     

Magnetic properties of Cd(1 - x)Mn(x)Te/C nanocrystals

Mn doped CdTe nanocrystals coated by carbon (Cd(1 - x)Mn(x)Te/C) were synthesized by a one-step, kinetically controlled solid state reaction under autogenic pressure at elevated temperatures. Electron microscopic analysis confirmed that the 40-52 nm Cd(1 - x)Mn(x)Te core was encapsulated by a 6-9 nm carbon shell. The efficient doping by Mn(2+) in the zinc blende Cd(1 - x)Mn(x)Te lattice, up to an atomic ratio of Mn/Cd of 0.031, was confirmed from electron paramagnetic resonance (EPR) experiments. In the case of higher doping, it is likely that manganese is partially expelled to the nanocrystal surface. All the doped samples exhibit ferromagnetism at room temperature. The lowest doped sample has the highest magnetic moment (1.91 ± 0.02 μ(B)/Mn). The more concentrated samples exhibit weaker ferromagnetic interactions, probably due to an incomplete coupling between carriers in the host CdTe semiconductor and dopant spins.     

Bulk Bridgman growth of cadmium mercury telluride for IR applications

Cadmium mercury telluride (CMT, CD_xHg_1-xTe) is the pre-eminent infrared material, despite the difficulties associated with the production and subsequent processing of this ternary compound. By varying the x value the material can be made to cover all the important infrared (IR) ranges of interest. The first technique developed was the basic vertical Bridgman process with typical crystal dimensions of 13 mm diameter and 150 mm length. We found it necessary to purify both the mercury and the tellurium on-site before use to obtain the required electrical properties. There is marked segregation of the matrix elements in Bridgman growth that is both a disadvantage and an advantage. Its disadvantage is that the yield of material in terms of composition for the two most common regions required (x=0.21 and 0.3 for 8–14 and 3–5 m atmospheric transmission windows, respectively) is low. The advantage is that both regions of interest are produced in the same crystal. A further advantage is that segregation of impurities also occurs and leads to low background donor levels in Bridgman material. This Bridgman material is used exclusively for photoconductive IR detectors that require n-type material. The main disadvantages of the Bridgman technique are that material is non-uniform in composition in the radial direction, as well as in the growth direction, and there are numerous grain and sub-grain boundaries. An improved process was developed at BAE Systems based on the accelerated crucible rotation technique (ACRT). Here, growth ampoules are subjected to periodic acceleration/deceleration in their rotation, rather than constant rotation as in the Bridgman process. The major effect of this is to stir the melt during growth and produce flatter solid/liquid interfaces. This, in turn, improves the radial and axial compositional uniformity of the material, normally by a factor of at least ten-fold. The only drawback is that the material is now p-type as grown and must be annealed in mercury vapor to convert it to n-type. An additional marked advantage of ACRT is that the improved radial compositional uniformity enables larger diameter material to be considered. We are currently growing 20 mm diameter, 200 mm long crystals of 0.5 kg weight with acceptable uniformity of composition and good electrical properties for current photoconductive detector programs. © 2001 Kluwer Academic Publishers     

Thermal Diffusivity,Effusivity, and Conductivity of CdMnTe Mixed Crystals

\(\hbox {Cd}_\mathrm{1-x}\hbox {Mn}_\mathrm{x}\hbox {Te}\) mixed crystals belong to a class of materials called “semimagnetic semiconductor” or diluted magnetic semiconductor with the addition of magnetic ions such as \(\hbox {Mn}^{2+}\) implemented into the crystal structure. The crystals under investigation were grown from the melt by the high-pressure high-temperature modified Bridgman method in the range of composition \(0<\mathrm{x}<0.7\) . Thermal properties of these compounds have been investigated by means of photopyroelectric calorimetry in both back and front detection configurations. The values of the thermal diffusivity and thermal effusivity were derived from experimental data. The thermal conductivity of the specimens was calculated from the simple theoretical dependencies between thermal parameters. The influence of the Mn concentration on the thermal properties of \(\hbox {Cd}_\mathrm{1-x}\hbox {Mn}_\mathrm{x}\hbox {Te}\) crystals has been presented and discussed.     

Bulk growth of near-IR cadmium mercury telluride (CMT)

Cadmium mercury telluride (CMT, Cd_xHg_1?xTe) is still the pre-eminent infrared material, despite the difficulties associated with its production and subsequent processing. By varying the x value, the system can be made to cover all the important infrared (IR) ranges of interest. The two most common regions required are x～0.21 and 0.3 for 8–14 and 3–5 μm atmospheric transmission windows, that is, long wave, LW, and mid wave, MW, respectively. Recently we have extended the growth process to produce both very long wavelength and near-IR material for various applications. This paper focuses on the work undertaken to produce near-IR material, where higher starting x values are used. Growth takes place in simple 2-zone furnaces with the pure elements contained in thick-walled high-purity silica ampoules. The thick ampoule walls are needed to contain the high (up to ～70 atm) mercury vapor pressures within the ampoules. An improved ampoule seal-off procedure was developed to enable us to grow at the higher temperatures (hence higher pressures) needed for these higher x start crystals. The accelerated crucible rotation technique (ACRT) modification to the basic Bridgman process is used to grow the crystals. Here, ampoules are subjected to periodic acceleration/deceleration in their rotation, rather than constant rotation as in the Bridgman process, which stirs the melt during growth and produces flatter solid/liquid interfaces. This, in turn, improves the radial and axial compositional uniformity of the material. An additional advantage of ACRT is that the improved radial compositional uniformity enables larger diameter material to be considered. We are currently growing 20 mm diameter, 200 mm long crystals of ～0.5 kg weight with good uniformity of composition. The assessment of the near-IR material has included wavelength mapping of both radially cut slices and axially cut planks. The latter gives useful information on the shape and change in the solid/liquid interface as growth proceeds. Quenching experiments reveal actual solid/liquid interfaces that confirm the findings of the wavelength mapping. Images taken with an IR camera reveal features in slices, for example, cracks, inclusions of second phase and swirl patterns, the origin of the latter is unknown.     

Cd/sub 1-x/Mn/sub x/Te semimagnetic semiconductors for ultrafast spintronics and magnetooptics

We present ultrafast optical characterization of Cd/sub 1-x/Mn/sub x/Te single crystals with high (x>0.5-Mn) concentration, studied by magnetooptical sampling and time-resolved magnetization modulation spectroscopy. We have demonstrated that the dynamics of both Mn spins and carrier spins in Cd/sub 1-x/Mn/sub x/Te is extremely fast (in the subpicosecond range), making the nanostructures based on this material very promising for applications in spintronics and magnetooptics.     

Solidification Studies of 3003 Aluminium Alloys with Cu and Zr Additions

The effects of Cu and Zr additions, on the microstructure formation, precipitation and ingot cracking, in commercial 3003 Al alloys have been studied. The investigation was carried out by characterizing the grain structure in DC-cast rolling ingots, and studying the solidification microstructure of Bridgman directionally solidified samples. To better understand the influence of the different Cu and Zr contents on the phase precipitations, differential thermal analysis (DTA) experiments were performed. Results from the ingot microstructure analysis show that in commercial alloys with relatively high contents of Cu and Zr, no significant differences in measured grain sizes compared to conventional 3003 Al alloys could be found. However, only Zr containing alloys exhibited significantly larger grain sizes. Increased grain refiner and/or titanium additions could compensate for the negative effects on nucleation normally following Zr alloying. Different types of precipitates were observed. Based on DTA experiments, increased Cu and Zr contents resulted in the formation of Al2Cu phase, and increased solidification range. It was also found that increased Mn content favors an early precipitation of Al6(Mn,Fe) giving relatively coarse precipitates. It was concluded that the Cu alloying has a detrimental effect on hot tearing.     

Enhancement of the yield of high-quality ingots in the zone-melting growth of p-type bismuth telluride alloys

The influences of zone melting growth speed on the thermoelectric properties of p-type bismuth telluride alloys were investigated. When the growth speed was fast, thermoelectric properties were uniform along ingots, as the composition of the molten zone did not change significantly. On the other hand, when growth speed was slow, thermoelectric properties varied along ingots due to the change of the solidified composition determined by the composition of a molten zone. The maximum figure of merit appeared in the middle of an ingot grown at slow growth speed. In the present study, the molten zone leveling method was developed as an attempt to extend theregion with high figure of merit. The basic idea of the method was to preserve a uniform composition of liquid at the solid-liquid interface during growth of an ingot so as to obtain a uniform composition of precipitated solids. Ingots composed of two sections with different compositions were used to control the accumulation of Te within the molten zone. As a result, high figure of merit could be obtained over more than 90% of ingot when zone melting growth speed was slow.     

Crystal growth and reflectivity studies of Zn1-xMnxTe crystals

Single crystals of Zn_1-xMn_xTe were prepared by vertical Bridgman crystal growth method for different concentrations of Mn. Chemical analysis and reflectivity studies were carried out for compositional and band structure properties. Microscopic variation in composition between starting and end compounds was observed from EDAX analysis. Linear dependence of fundamental absorption edgeE ₀as a function of Mn concentration (x) was expressed in terms of a straight line fit and a shift in E₀ towards higher energy was observed in reflectivity spectra of Zn_1-xMn_xTe.     

温度梯度溶液法生长的Cr掺杂的ZnTe晶体的表征

以CrTe作为掺杂源、以Te作为溶剂, 用温度梯度溶液法生长了Cr掺杂的ZnTe晶锭。晶锭头部的晶粒尺寸较大(>10 mm×10 mm), 且Te夹杂相较少。Te夹杂相的大小、形状和分布可以反映晶锭中的温场分布。晶锭的径向非对称温场导致富Te相沿径向非对称分布。Te夹杂相在温度梯度作用下的热迁移会导致其相互融合长大、变长。Te夹杂相也会在晶体中引入裂纹和空洞等缺陷。部分未被掺入ZnTe中的CrTe富集于固液界面处, 表明温度梯度溶液法生长晶体时具有一定的排杂作用。Cr掺杂的ZnTe晶体的电阻率(约1000 Ω·cm)高于未掺杂的ZnTe(约300 Ω·cm)。Cr掺杂晶体在约1750 nm处的吸收峰表明Cr²⁺离子被成功地掺入了ZnTe中。但是Cr掺杂后晶体的红外透过率降低, 表明Cr掺杂引入了较多的缺陷。     

坩埚下降法生长钨酸镉单晶的光学均匀性

采用垂直坩埚下降法生长出大尺寸CdWO₄单晶, 通过DSC/TG、XRD、电子探针、透射光谱和X射线激发发射光谱对单晶进行了测试表征, 分析了单晶生长过程中熔体挥发情况和单晶化学成分变化, 研究了所生长单晶的光学均匀性的变化规律. 结果表明, CdWO₄单晶生长过程存在比较严重的熔体挥发, 且熔体中CdO比WO₃更加易于挥发; CdWO₄单晶的化学组成存在不同程度缺Cd的特征, 初期生长晶体的n(Cd)/n(W)比相对高, 后期生长晶体的n(Cd)/n(W)比持续减小, 相应地单晶在380~550nm区域的光透过率略有降低, X射线激发发光强度有所降低, 且发光波长出现略微红移的趋势. 通过提高多晶料纯度、减少熔体挥发和氧气氛退火处理, 可以改善坩埚下降法生长CdWO₄单晶的光学均匀性.     

溅射功率对CdZnTe薄膜成分和结构的影响

采用Cd0.9Zn0.1Te晶体作为溅射靶在玻璃衬底上利用磁控溅射法制备出CdZnTe薄膜,研究了溅射功率对CdZnTe薄膜的成分、结构特性的影响。制备的CdZnTe薄膜是具有闪锌矿结构的多晶薄膜,沿（111）择优取向。随着溅射功率的增大,薄膜沉积速率增大,薄膜结晶质量提高。采用晶体靶Cd0.9Zn0.1Te溅射CdZnTe薄膜时,无论是在何种功率下CdZnTe薄膜中的Cd原子成分均高于Te原子成分,Cd原子表现为择优溅射原子。