非晶态碲镉汞的暗电导率和吸收边

研究了非晶态碲镉汞(x=0.2)薄膜的暗电导率随温度变化关系,发现非晶态结构的碲镉汞材料具有明显的半导体特性,其室温禁带宽度在0.88～0.91 eV之间,与通过光学方法获得的结果相符.在80～240K的温度区间非晶态碲镉汞(x=0.2)的暗电导率从1×10-8Ω-1·cm-1缓慢增大到5×10- 8Ω-1-cm-1,温度大于240K时,其电导率剧烈增大到1×10-5Ω-1·cm-1,说明在240K附近非晶态碲镉汞材料的导电机制发生了变化,这对非晶态碲镉汞材料的应用研究具有重要意义.还研究了退火过程对非晶态碲镉汞薄膜电导率的影响,结果表明140℃退火后非晶态碲镉汞薄膜发生了部分晶化.     

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.     

非晶态碲镉汞薄膜晶化过程的椭圆偏振光谱研究

采用椭圆偏振光谱技术研究了非晶态碲镉汞薄膜在不同退火条件下的结构性能.结果表明非晶态碲镉汞薄膜在退火过程中的成核晶化是在薄膜内部均匀发生的,对于不同晶化程度的薄膜,其光学常数谱具有明显的特征,通过对光学常数谱的分析研究可以对非晶态碲镉汞薄膜的晶化程度进行量化表征,从而控制退火条件,优化材料质量.     

The direct determination of the vacancy concentration and P-T phase diagram of Hgin0.8Zn0.2Te by dynamic mass-loss measurements

A modified mass-loss measurement technique is employed, for the first time, for the direct, in-situ determination of the metal vacancy formation in (Hg_0.8Zn_0.2)_1-yTe_y,(s). The metal vacancy concentrations are determined between 350 and 650° C for four different compositions(y) within the homogeneity region and range from 1.7 to 6.6 × 10¹⁹ cm^-3. The enthalpy of formation of a singly-ionized metal vacancy is derived to be between 0.32 and 0.72 eV depending upon the deviation from stoichiometry (compositiony). Com-pared to the recent data on HgTe(s), these experimental results show a slight but sig-nificant increase in the enthalpy of vacancy formation from HgTe to Hg_0.8Zn_0.2Te. These data provide the first, direct experimental evidence, in terms of vacancy formation en-ergy, supporting theoretical predictions of the bond strengthening effect of Zn for the latter alloy system. Based on the simultaneously determined equilibrium Hg partial pressures within the homogeneity range, the vacancy concentration-partial pressure iso-therms are constructed. The Hg partial pressures are also measured along the three-phase boundaries of the solid solutions, and these are in close agreement with published data obtained by optical absorption measurements. A considerable part of the P-T phase diagram is, thus, established in this work.     

Cd0.8Mn0.2Te晶体的生长及其性能

通过适当的工艺措施,采用传统布里奇曼法生长了尺寸为φ30mm×120mm的Cd0.8Mn0.2Te晶体.对晶体进行了X射线粉末衍射、X射线双晶摇摆曲线、紫外-可见光光谱、红外透过率及电阻率测试.测试结果表明,晶体结构为立方型,半峰宽较低,吸收边为720nm,对应禁带宽度为1.722eV,晶体的红外透过率和电阻率都较高.并讨论了晶体中的缺陷对红外透过率和电阻率的影响.     

Fast growth of Cd1−xZnxTe single crystals by physical vapor transport

Good quality single crystals of Cd_1−xZn_xTe (x=0.04, 0.08, and 0.115) were obtained by the very fast vapor growth technique developed in this laboratory. The abundance of lamellar twins seems to be less than that in CdTe grown under the same conditions. Chemical etching results indicate a similar quality of the vapor grown crystals to those obtained from melt growth. The overall compositions of the crystals are uniform and approach those of the initial source material with increasing amount transported.     

Growth and properties of Hg1-x Cdx Te epitaxial layers

The growth of epitaxial layers of mercury-cadmium-telluride (Hg_1-xCd_xTe) with relatively low x (0.2-0.3) from Te-rich solutions in an open tube sliding system is studied. The development of a semiclosed slider system with unique features permits the growth of low x material at atmospheric pressure. The quality of the films is improved by the use of Cd_1-yZ_yTe and Hg_1-xCd_xTe substrates instead of CdTe. The substrate effects and the growth procedure are discussed and a solidus line at a relatively low temperature is reported. The asgrown epitaxial layers are p-type with hole concentration of the order of 1·10¹⁷ cm⁻³, hole mobility of about 300 cm²·V⁻¹ sec⁻¹ and excess minority carrier life-time of 3 nsec, at 77 K.     

Transport properties of undoped Cd0.9Zn0.1Te grown by high pressure bridgman technique

The electron drift mobility of undoped Cd_0.9Zn_0.1Te grown by high-pressure Bridgman method is measured by a time-of-flight technique. The sample shows a room temperature mobility and mobility lifetime product of 950 cm²/Vs and 1.6 × 10⁻⁴cm²/V, respectively. The mobility increases monotonically with decreasing temperature to 3000 cm²/Vs at 100 K. The dominant scattering mechanism for the electron transport is discussed by comparing with the theoretical mobility obtained by iterative solution of the Boltzmann equation.     

Effects of growth conditions on the composition of CVT and PVT grown Hg1-x Cd x Te epitaxial layers

Single crystal epitaxial layers of Hg_1-x Cd _x Te were grown on CdTe substrates employing the chemical and physical vapor transport techniques. Different growth temperatures and various pressures of HgI₂ as a transport agent were used while the source materials had compositions of eitherx = 0.4 orx = 0.6. The epilayers are of nearly uniform composition to a depth of about one-half of the layer thickness. The Hgl₂ pressure and the growth temperature used for the growth experiments have significant effects on the layer composition. The desired epilayer composition ofx = 0.2 can be achieved with either source compositions by properly adjusting the HgI₂ pressure and the growth temperature.     

Transient behavior of Hg1−xCdxTe film growth on 3° off-(100) CdTe substrates by chemical vapor transport

The effects of substrate misorientation on Hg_1−xCd_xTe films, deposited on 3° off-(100) CdTe substrates by chemical vapor transport (CVT), have been studied for the first time using a transient growth technique. The morphological evolution of Hg_1−xCd_xTe films deposited on the vicinal CdTe substrates at 545°C shows a transition from three-dimensional islands to two-dimensional layer growth. The time and thickness required for the above morphological transition is about 0.75 h and 7 μm, respectively, under present experimental conditions. The pronounced long-range-terrace surface morphology of the Hg_1−xCd_xTe films illustrates the strong effects of the misorientation of the CdTe substrates and of the growth kinetics on the CVT growth of this hetero-epitaxial system. The transient behavior of the surface morphology, of the surface composition, and of the growth rate all reveal the influences of the 3° misorientation of the (100) CdTe substrates on the Hg_1−xCd_xTe epitaxy. The experimental mass flux results of the Hg_1−xCd_xTe-HgI₂ CVT system under transient and steady-state conditions can be related to the surface kinetics and to the thermodynamic properties of the system. The combined results show that the interface kinetics are not fixed in the transient regime and that they are coupled to the vapor mass transport.     

Slider LPE of Hg1-xCdxTe using mercury pressure controlled growth solutions

Homogeneous, nearly perfect single crystals of Hg_1-xCd_xTe are extremely difficult to prepare due primarily to the high vapor pressure of mercury. However, epitaxially grown Hg_1-xCd_xTe layers have a high potential for yielding material of a substantially higher quality. Using a new, open-tube, horizontal slider-type liquid phase epitaxial (LPE) growth technique, in which mercury pressure controlled growth solutions are used, a high degree of growth solution compositional control has been demonstrated. LPE layers of Hg_1-xCd_xTe have been grown on CdTe substrates and their high quality has been confirmed by optical, transport and electron microprobe measurements. Layer thicknesses are uniform and have been varied from 5 to 40 μ by changing the degree of supercooling or the growth time. An electron carrier concentration as low as 8.6 × 10¹⁵/cm³ and electron Hall mobilities up to 2.8 × 105 cm²/V-sec at 77K have been measured on in situ annealed samples. This work was sponsored by the Department of the Air Force and the U.S. Army Research Office.     

剩余杂质对Hg_(0.8)Cd_(0.2)Te晶体光吸收的影响

研究了Hg_(0.8)Cd_(0.2)Te晶体经吸除工艺处理前后的透射光谱,发现样品经吸除处理后的光吸收发生明显变化,分析认为因吸除工艺降低了样品内的剩余杂质含量,从而减少了杂质参与的光吸收,利用受主“掺杂”实验进一步验证了上述解释。     

In掺杂CdMnTe晶体的Te气氛退火研究

Thermal annealing in Te vapor atmosphere was adopted to improve the properties of indium-doped Cd_1-xMn_xTe（x=0.2,CdMnTe） wafers grown by the vertical Bridgman method.The wafers before and after annealing were characterized by measuring the Te inclusions,etch pit density（EPD）,Mn composition,resistivity, and impurity.IR transmission microscopy and EPD measurements revealed that the densities of Te inclusions reduced from（5-9）×10⁴ cm^-3 to（2-4）×10⁴ cm^-3 and EPD from 10⁵ cm^-2 to 10⁴ cm^-2 after annealing. NIR transmission spectroscopy showed that the Mn composition increased by 0.002-0.005 mole fractions during the annealing.The resistivity of the wafers improved from（2.0-4.5）×10⁸Ω·cm to（1.7-3.8）×10⁹Ω·cm,which suggested that the deep-level donor of Te antisites was successfully introduced after annealing.Inductively coupled plasma-mass spectrometry（ICP-MS） revealed that the concentrations of impurities in the wafer decreased,which indicated the purifying effects of Te vapor annealing on the wafers.All the results demonstrate that the Te vapor annealing of the indium-doped CdMnTe crystal has positive effects on the crystallinity,resistivity and purity of CdMnTe wafers.     

Compositional dependence of infrared phonon parameters for Hg1-xCdxTe

The full set of Lorentzian oscillator parameters describing the two-mode phonon behavior in Hg_1-x-jCd_xTe is reported. A new analysis of reflectivity spectra combined with existing results gives the most accurate available values for the CdTe-like and HgTe-like transverse optical frequency, strength and (for the first time) damping constant vs CdTe fractionx at room, liquid nitrogen and liquid helium temperatures. Polynomial fits vsx for each parameter are provided for use in characterizing Hg_1-xCd_xTe and the HgTe-CdTe superlattice.     

高阻碲锌镉单晶体的生长及其性能观测

报道了采用富Cd原料的无籽晶垂直布里奇曼法生长高阻碲锌镉Cd0.8Zn0.2Te(CZT)单晶体的新工艺,对所生长的晶体作了X射线衍射分析、红外透过率测试、光吸收截止波长测量及电学性能测试.晶体在4400～450cm-1范围内的红外透过率达到50%,截止吸收波长为787.6nm,带隙为1.574eV,室温电阻率达到2×1010Ω·cm,已接近本征Cd0.8Zn0.2Te半导体的理论值.用该晶体制作的核探测器在室温下对241Am和109Cd放射源均有响应,并获得了比较好的241Am-59.5keV吸收谱.结果表明改进的方法是一种生长室温核辐射探测器应用的高阻CZT单晶体的简便有效的新方法.     

Structure investigation on Hg1−xCdxTe liquid phase epitaxial films grown by the meltetch technique

Hg_1−xCd_xTe films were grown by a modified meltetch liquid phase epitaxial (LPE) technique which includes both substrate and epilayer etchback steps. The crystal quality of epilayer has been investigated by means of transmission electron microscopy, scanning electron microscopy, and double crystal x-ray diffraction. It has been found that adequate meltetch of the substrate at the beginning of LPE provides a fresh and flat surface for epitaxial growth, while epilayer meltetch at the end of LPE may prevent spurious melt sticking.     

Oxidation of Hg1−xCdxTe studied with surface sensitive techniques

We report the use of surface sensitive electron spectroscopies to monitor the initial steps of formation of a native oxide on atomically clean cleaved Hg_l-xCd_xTe single crystal surfaces in ultrahigh vacuum (UHV). Here the oxide is formed by oxygen excited by the presence of an operating ion gauge. During the reaction, the composition of the surface region of the substrate was found to change, with a net loss of Hg from the surface. Parallel studies of the compositions of thick anodic oxides using sputter profiling techniques showed only small amounts of Hg in the anodic oxides. On leave from Odense University, Denmark.     

Passivation of Hg1−xCdxTe by photochemical native oxidation: Growth characteristics

The growth of photochemical native oxides on x = 0.3 bulk wafers of n-type Hg_1−xCd_xTe has been studied with relation to growth temperature, gas flow rate, oxidizing ambient, and the wavelengths of ultraviolet radiation needed to drive the process. The growth was found to proceed with a relationship of thickness ∝ (time)^1/3 for both O₂ and N₂O ambients. An observed inverse relationship between thickness, and both growth temperature and gas flow rate, indicates a growth process that is either competing with parasitic quenching of the excited oxidizing species produced, or a diffusion controlled process, in which different growth conditions produce oxides with a variety of diffusion characteristics. The physical and optical properties of the photochemical oxides were found to be similar to anodic oxides. Rutherford backscattering spectra have shown the composition of the films to be highly dependent on growth conditions with films grown in O₂ ambients generally showing a higher mercury content than those grown in N₂O. Further, for growths in O₂ atmospheres, those carried out at lower temperatures result in more mercury in the oxide and at the oxide/mercury cadmium telluride interface when compared to those grown at higher temperatures.     

Passivation of Hg1-xCdxTe by photochemical native oxidation: Quantitative analysis of oxide composition

The composition of photochemically grown native oxides on Hg_1-xCd_xTe (x = 0.3) has been analyzed and depth profiled using x-ray photoelectron spectroscopy and Rutherford backscattering spectroscopy. The oxide films were grown in either N₂O or O₂ ambients, and differences in the oxidation process were examined by varying the time and temperature of oxide growth. Under all growth conditions, oxides grown in an O₂ ambient exhibited a higher Hg concentration in the bulk oxide region when compared to N₂O grown oxides. The Hg/Te ratio of all the oxides was found to be less than the starting Hg_1-xCd_xTe substrates and, in some cases, this may be leading to an accumulation of Hg in the oxide/Hg_1-xCd_xTe interface region. For growths at higher temperatures (∼75°C), the excess Hg was seen to move from the oxide/Hg_1-xCd_xTe interface region to the oxide surface. In O₂ ambients, the Hg accumulated at the surface of the oxide whereas for growths in N₂O, it was lost to the ambient. Previous results on photochemical oxidation of Hg_1-xCd_xTe show an inverse relationship between oxide growth rate and temperature. Evidence obtained in this study from oxide compositions, depth profiles and annealing at higher temperatures, suggest that this relationship between oxide growth rate and temperature is primarily due to temperature induced differences in the oxidizing ambient, and not the result of a change in the film growth mechanism due to changing diffusion characteristics with temperature.