The direct determination of the vacancy concentration andP-T phase diagram of Hg0.8Cd0.2Te and Hg0.6Cd0.4Te by dynamic mass-loss measurements

A modified mass-loss measurement technique is employed, for the direct,in- situ determination of the metal vacancy formation in (Hg_1x2212;itxCd _x )_1−y Te _y (s) withx = 0.2 and 0.4. Forx = 0.2, the metal vacancy concentrations are determined between 336 and 660° C for three different compositions(y) within the homogeneity region and range from 2.4 to6.8 x 10¹⁹cm₋₃. The enthalpy of formation of a singly-ionized metal vacancy is derived to be between 0.17 and 0.45 eV depending upon the deviation from stoichiometry (compositiony). Forx= 0.4, three samples of different y-values give the metal vacancy concentrations from 1.9 to 5.5 x 10¹⁹cm⁻³ between 316 and 649° C, and the enthalpy of vacancy formation between 0.25 and 0.40 eV. Compared to the recent data on HgTe(s), these experimental results show a slight but significant decrease in the enthalpy of vacancy formation from HgTe to Hg_0.8Cd_0.2Te, which supports theoretical predictions of the bond weakening effect of Cd for the latter alloy system. Based on the simultaneously determined equilibrium Hg partial pressures within the homogeneity range, the vacancy concentration-partial pressure isotherms are constructed. The Hg partial pressures are also measured along the three-phase boundaries of the solid solutions of bothx = 0.2 and 0.4, and these are in close agreement with published data obtained by optical absorption measurements.     

The effect of annealing temperature on the carrier concentration OF Hg0.6Cd0.4Te

The carrier concentration dependence of Hg_0.6Cd_0.4Te on annealing temperature for the Hg and Te saturation condi-tions is presented in this paper. At low annealing tempera-tures, T_A < 350‡ C, residual donor impurities apparently limit the carrier concentration. In contrast, at higher annealing temperatures, 350‡ C < T < 700‡ C, the stoichio-metric acceptor density is increased such that the residual donors are compensated and the material is converted to p-type with an acceptor density as large as 10¹⁷ cm⁻³ . An empirical expression describing this dependence of the acceptors on annealing temperature is given for both the Hg and Te saturation condition: P (Hg saturation) = 1.46 × 10²² exp (−0.84/kT_A), P (Te saturation) = 1.90 × 10¹⁸ exp (−0.15/kT_A). Supported in part by Air Force Materials Laboratory, WPAFB, Ohio under Contract AF61533-C-74-5041.     

Annealing experiments in heavily arsenic-doped (Hg,Cd)Te

Arsenic doped molecular beam epitaxy (MBE) (Hg,Cd)Te films were grown on (Cd,Zn)Te substrates. The concentration of arsenic was varied from 5 x 10¹⁸ cm^-3 to 1 x 10²⁰ cm^-3. After the growth, the epitaxial layers were annealed at various partial pressures of Hg within the existence region of (Hg,Cd)Te at temperatures ranging from 400 to 500°C. Hall effect and resistivity measurements were carried out subsequent to the anneals. 77K hole concentration measurements indicate that for concentrations of arsenic <10¹⁹ cm⁻³, most of the arsenic is electrically active acting as acceptors interstitially and/or occupying Te lattice sites at the highest Hg pressures. At lower Hg pressures, particularly at annealing temperatures of 450°C and higher, compensation by arsenic centers acting as donors appears to set in and the hole concentration decreases with decrease in Hg pressure. These results indicate the amphoteric behavior of arsenic and its similarity to the behavior of phosphorus in (Hg,Cd)Te previously inferred by us. A qualitative model which requires the presence of arsenic occupying both interstitial and Te lattice sites along with formation of pairs of arsenic centers is conjectured.     

The growth and characterization of (211) and (133) Oriented (Hg,Cd)Te epilayers (211)B GaAs by organometallic vapor phase epitaxy

The growth of CdTe buffer layers on (211)B GaAs substrates by organometallic vapor phase epitaxy (OMVPE) was studied, and it was found that, depending on the growth conditions, either the (211) or (133) epitaxial orientation could be formed. In some cases, an epilayer showing a mixed (211) and (133) orientation was also observed. The influence of several growth parameters on the orientation of the CdTe layer was investigated, and it was found that the Te/Cd ratio, together with the growth temperature, have the most significant effect in determining the epilayer orientation. From these results, it was then possible to select nominally optimized growth conditions for CdTe buffer layers of both orientations. (Hg,Cd)Te layers of the same orientations could then be grown and characterized. Although double crystal x-ray diffraction measurements indicated a somewhat better crystalline perfection in the (133) (Hg,Cd)Te layers, these layers showed a poor surface morphology compared to the (211) orientation. Measurement of etch pit densities also indicated defect densities to be typically half an order of magnitude higher in the (133) orientation. Diodes were formed by ion implantation in both orientations and significantly better results were obtained on the (211) (Hg,Cd)Te layers.     

Interdiffusion behavior of Hg in HgTe/CdTe superlattices grown on Cd0.96Zn0.04 Te (211)B substrates by molecular beam epitaxy

Double-crystal x-ray rocking curve (DCRC) and secondary-ion mass-spectroscopy (SIMS) measurements have been performed to investigate the effect of rapid thermal annealing on the interdiffusion behavior of Hg in HgTe/CdTe superlattices grown on Cd_0.96Zn_0.04Te (211)B substrates by molecular beam epitaxy. The sharp satellite peaks of the DCRC measurements on a 100-period HgTe/CdTe (100Å/100Å) superlattice show a periodic arrangement of the superlattice with high-quality interfaces. The negative direction of the entropy change obtained from the diffusion coefficients as a function of the reciprocal of the temperature after RTA indicates that the Hg diffusion for the annealed HgTe/CdTe superlattice is caused by an interstitial mechanism. The Cd and the Hg concentration profiles near the annealed HgTe/CdTe superlattice interfaces, as measured by SIMS, show a nonlinear behavior for Hg, originating from the interstitial diffusion mechanism of the Hg composition. These results indicate that a nonlinear interdiffusion behavior is dominant for HgTe/CdTe superlattices annealed at 190°C and that the rectangular shape of HgTe/CdTe superlattices may change to a parabolic shape because of the intermixing of Hg and Cd due to the thermal treatment.     

Low-temperature annealing of (Hg,Cd)Te

Many methods for the employment of (Hg,Cd)Te alloys employ anneals at temperatures <300°C to convert the p type left over from the growth process or to adjust the concentration of the native acceptors. An investigation of the kinetics of this annealing process has been performed as functions of (1) vacancy concentration; (2) composition, or the CdTe mole fraction in the alloy; and (3) temperature. If these anneals are carried out under mercury-saturated conditions, the tellurium precipitates in the material, which result either from the growth process or from specific thermal histories, are annihilated by in-diffusing mercury, which results in a significant multiplication of dislocations. This interface, delineated by defect etching, has been employed to investigate the kinetics of the annealing process. These results will be unaffected by the uncertainties introduced in determining this interface by electrical measurements, which arise from incomplete ionizations of the metal vacancies at 77 K for Hg_1−xCd_xTe with CdTe mole fractions exceeding ∼0.26. The annealing rate appears to be strongly dependent on both the temperature and composition of the alloy, decreasing with increasing CdTe mole fraction, within 0.15 and 0.5, with the behavior resembling a composition-dependent, activated-diffusion process. The depth of the interface appears to vary inversely as the root of the metal-vacancy concentration.     

性能稳定的铌酸锶钡钾钠晶体

铌酸锶钡钾钠晶体的掺杂改性试验表明，铜可有效地稳定极化，从而得到性能稳定的晶体。本文并对铜离子稳定作用进行了初步解释。     

Molecular beam epitaxy of CdTe and Hg1-xCdxTe ON GaAs (100)

Using the molecular beam epitaxial (MBE) technique, CdTe and Hg_1-xCd_xTe have been grown on Cr-doped GaAs (100) sub-strates. A single effusion cell charged with polycrystal-line CdTe is used for the growth of CdTe films. The CdTe films grown at 200 °C with a growth rate of ~ 2 μm/hr show both streaked and “Kikuchi” patterns, indicating single crystalline CdTe films are smoothly grown on the GaAs sub-strates. A sharp emission peak is observed at near band-edge (7865 Å, 1.577 eV) in the photoluminescence spectrum at 77 K. For the growth of Hg_1-xCd_xTe films, separate sources of HgTe, Cd and Te are used. Hg_0.6Cd_0.4Te films are grown at 50 °C with a growth rate of 1.7 μm/hr. The surfaces are mirror-smooth and the interfaces between the films and the substrates are very flat and smooth. As-grown Hg_0.6Cd_0.4Te films are p-type and converted into n-type by annealing in Hg pressure. Carrier concentration and Hall mobility of an annealed Hg_0.6Cd_0.4Te film are 1 × 10¹⁷ cm^?3 and 1000 cm²/V-sec at 77 K, respectively.     

CuO掺杂Ba_(0.6)Sr_(0.4)TiO_3陶瓷的结构与性能

采用传统陶瓷制备工艺,以容差因子为依据进行CuO掺杂,制备了可在较低温度烧结成瓷的Ba_(0.6)Sr_(0.4)TiO_3(BSTO)基陶瓷.结果表明,w(CuO)=0.5%～4.0%的BSTO基陶瓷可在1 200 ℃烧结成瓷,且不会引入杂相.介电性能测试表明,在室温低频下,随CuO掺杂量的增加,BSTO陶瓷的介电常数增加,而介电损耗降低;在微波频段下,BSTO基陶瓷的介电常数和介电损耗均随CuO掺杂量的增加而增大.可调性测试表明,在1 kV/mm的直流偏压下,各BSTO基陶瓷掺杂样的可调性均大于10%,其中,试样w(CuO)=1%的可调性达到13.2%.     

电流控制LPE生长In_（1－x）Ga_xAs_yP_（1－Y）

用电流控制液相外延（ＣＣＬＰＥ）方法首次在（１００）ＩｎＰ衬底上成功地生长出Ｉｎ１－ｘＧａｘＡｓｙＰ１－ｙ（０．３０＜ｘ＜０．４７，０．７０＜ｙ＜０．９６）外延层，并对外延层特性进行了详细研究，提出在ＩｎＰ衬底上生长电外延层的机理，推导出生长动力学的理论模型，该模型与上述实验结果十分吻合。     

(Ba1-xSrx)(Zn1/3Nb2/3)O3固溶体系统第二相的研究

研究了(Ba1-xSrx)(Zn1/3Nb2/3)O3(BSZN)固溶体系统在烧结中生成的第二相,分析了第二相的分布、形貌、形成规律、机理以及对介电性能的影响。研究表明,系统的主晶相为BSZN,同时生成了大量的第二相——Ba5Nb4O15(、Ba5-xSrx)Nb4O15(x=0~5)、Ba2Nb2O7、BaNb2O6等。第二相的生成是由于ZnO的挥发造成的;烧结温度越高、烧结时间越长,ZnO的挥发越多,第二相的含量也越多。第二相的形貌大部分为长方形的板状,样品的表面部分或完全被第二相所覆盖,且有少量呈粒状散布于晶粒之间。第二相的生成会对系统介质损耗产生不利的影响。     

Ga_(1-x)In_xAs_ySb_(1-y)/GaSb LPE生长及其性质研究

报导了在n型(100)GaSb衬底上,温度为520—530℃时,用液相外延的方法实现了组分在0≤x≤0.19,0≤y≤0.14范围内的Ga_(1-x)In_xAs_ySb_(1-y)四元合金半导体的生长。X射线双晶衍射,电子探针及光学显微镜的观察和分析测试表明:所得外延层的表面形貌和界面特性优良,组分分布和层厚均匀,晶格匹配及单晶性能良好。对外延层表面的氧化情况使用Auger能谱仪进行测试分析。另外,对生长中存在的一些问题进行了讨论。     

Ge_(0.4)Si_(0.6)/Si超晶格光探测器与Si波导的集成探讨:光场分析

对Ge0.4Si0.6／Si超晶格探测器光场进行了分析，并用京传播法（BPM）进行模拟。还探讨了这种探测器与Si波导的集成。在Si波导满足单模传输的条件下，推出光场在探测器中达稳态分布时的传播距离。另外还提出了这种探测器的设计长度与波导尺寸之间的依赖关系。     

The origin of hillocks in (Hg, Cd)Te grown by MOVPE

Dimethylcadmium, a precursor for the metalorganic vapor phase epitaxy of mercury cadmium telluride, has been shown to react with gallium arsenide to form trimethylarsine and dimethylarsine. An analogous reaction occurs between di-iso-propyltelluride and gallium arsenide to form iso-propylarsine and di-iso-propylarsine. It is proposed that if these reactions remove sufficient arsenic from a gallium arsenide substrate, metallic droplets will form on the wafer surface thereby creating the nucleation sites for hillocks. Analogous reactions have been observed between the precursors and a range of other substrates which can in turn be used to explain the origin of hillocks in epitaxial layers grown onto these materials.     

Ba_(0.6)Sr_(0.4)TiO_3/ZnNb_2O_6复相陶瓷的显微结构和介电性能

采用传统电子陶瓷工艺制备了Ba_(0.6)Sr_(0.4)TiO_3/ZnNb_2O_6(BSTZ)复相陶瓷,研究了ZnNb_2O_6含量对BSTZ陶瓷结构和介电性能的影响规律.结果表明,BSTZ复相陶瓷可在较低温度下烧结成瓷;陶瓷中除了Ba_(0.6)Sr_(0.4)TiO_3和ZnNb_2O_6两种主晶相,还有新相BaNb_(3.6)O_(10)生成;陶瓷的介电常数和介电损耗均随ZnNb2O6含量的增加而降低;当x(ZnNb_2O_6)=0.6(摩尔比)时,复相陶瓷在微波下的介电常数为74,介电损耗为0.043,可调性可达10.54%(1.0 kV/mm).     

液相外延生长In_xGa_(1-x)As_ySb_(1-y)/GaSb及其性质研究

本文利用液相外延方法,在较大组分范围内(0≤x≤0.17,0≤y≤0.12),成功地生长出了晶格匹配于(100)GaSb衬底的In_xGa_(1-x)As_ySb_(1-x)四元材料,并对其性质进行了实验观察和研究。结果表明,这种表面光亮、层厚均匀、异质结界面平直以及纯度较高、完整性好的外延薄膜是制作超长波长光电器件的理想材料。     

分子束外延HgCdTe/CdZnTe(211)B表面缺陷研究

HgCdTe材料的表面缺陷是造成探测器性能下降的主要原因之一。采用聚焦离子束（Focused Ion Beam, FIB）、扫描电子显微镜（Scanning Electron Microscope, SEM）和能量色散X射线光谱仪（Energy Dispersive X-ray Spectrometer, EDX）研究了碲锌镉（CdZnTe)基HgCdTe外延层的表面缺陷。通过分析不同类型缺陷形成的原因,确定缺陷起源于HgCdTe材料生长过程。缺陷的形状与生长条件关系密切。凹坑及火山口状缺陷与Hg缺乏/稍高生长温度、分子束源坩埚中材料形状变化造成的不稳定束流有关。金刚石状缺陷和火山口状/金刚石状复合缺陷的产生与Hg/Te高束流比、低生长温度相关。在5 cm×5 cm大小的CdZnTe(211)B衬底表面上生长出了组分为0.216、厚度约为6.06~7 μm的高质量HgCdTe外延层。同时还建立了缺陷类型与HgCdTe薄膜生长工艺的关系。该研究对于制备高质量HgCdTe/CdZnTe外延层具有参考意义。     

As Doping in (Hg,Cd)Te: An Alternative Point of View

Acceptor doping of many II–VI compound semiconductors has proved problematic and doping of epitaxial mercury cadmium telluride (MCT, Hg_1−x Cd _x Te) with arsenic is no exception. High-temperature (>400°C) anneals followed by a lower temperature mercury-rich vacancy-filling anneal are frequently required to activate the dopant. The model frequently used to explain p-type doping with arsenic invokes an amphoteric nature of group V atoms in the II–VI lattice. This requires that group VI substitution with arsenic only occurs under mercury-rich conditions either during growth or the subsequent annealing and involves site switching of the As. However, there are inconsistencies in the amphoteric model and unexplained experimental observations, including arsenic which is 100% active as grown by metalorganic vapor-phase epitaxy (MOVPE). A new model, based on hydrogen passivation of the arsenic, is therefore proposed.     

高介电(1–x)Ca_(0.7)Nd_(0.2)TiO_(3-x)Ba_(0.4)Sr_(0.6)TiO_3陶瓷微波介电特性

采用固相反应法制备了具有钙钛矿结构的(1–x)Ca_(0.7)Nd_(0.2)TiO_(3-x)Ba_(0.4)Sr_(0.6)TiO_3(0.05≤x≤0.5)陶瓷,并对其烧结行为、相组成、显微结构及微波介电性能进行了研究。结果表明:随着(Ba0.4Sr0.6)2+含量的增加,(1–x)Ca_(0.7)Nd_(0.2)TiO_(3-x)Ba_(0.4)Sr_(0.6)TiO_3(0.05≤x≤0.5)陶瓷的品质因数(Q·f)及谐振频率温度系数(τf)单调递减,而相对介电常数(εr)先升后小幅降低。当x=0.2,且烧结温度为1 450℃时,该介质陶瓷的微波介电性能为:εr=151.3,Q·f=5 900 GHz,τf=399.4×10–6/℃。与CaTiO_3(εr=160,Q·f=6 800 GHz,τf=850×10–6/℃)相比,Q·f和εr略微降低,τf有较大程度的减少,故此陶瓷体系有望替代CaTiO_3成为新一类高介电性微波陶瓷。     

与InP晶格相匹配的Ga_xIn_(1-x)P_yAs_(1-y)半导体的光学常数计算

采用半经验的紧束缚方法计算了与InP晶格相匹配的Ga_xIn_(1-x)P_yAs_(1-y)半导体的电子联合状态密度及介电常数虚部,并根据Kramers-Kronig关系式求得了光透明区的折射率常数.