环烷酸和其它萃取剂协同萃取稀土元素的化学

环烷酸是一种价廉容量大的萃取剂，在其中加入混合醇工业上已用于分离制取高纯Y_2O_3，并用于提纯氧化铕。为了扩大环烷酸的应用，我们对加有中性磷萃取剂及β－双酮类螯合剂的环烷酸协萃体系进行了较为系统的研究。测定了协萃体系萃取Nd(III)和Er(III)的协萃曲线，协萃剂的协萃能力强弱顺序为：PMBP＞TOPO＞BDBP＞DBBP＞TBP Er(III)＞Nd(III) TBP几乎没有协萃效应，当其在有机相中所占克分子而分数大于30％时，尤其如此，DBBP有类似的规律，其余协萃剂均无反协萃效应。测定单一稀土离子分配比随原子序数的变化可见协萃体系协萃重稀土的能力大于轻稀土。钇的萃取位置发生了显著的变化，主要是位于轻稀土组，在如有DBBP及TOPO的体系中移至了HO附近；随着平衡水相酸度的降低，钇有向原子序数增大的方向移动的趋势，而且中性磷萃取剂的萃取能力越大，钇的萃取位置变化越多，使其和镧系元素之间的分离因素有所下降。用解析法等研究了多元协萃络合物的组成及协萃反应机理，并计算了相应的表观协萃平衡常数及有机相加合反应平衡常数。考察萃取前后有机相的红外光谱可见中性磷萃取剂和环烷酸形成氢键的能力为：TBP＞DBBP＞BDBP＞TOPO和金属离子的配位能力为：TBP＜DBBP＜（BDBP）＜TOPO Nd(III)＜Er(III)找出了环烷酸配位后羧基的反对称及对称伸展振动，由二者之差指出羧基为螯合配位或双金属格式配位，P＝O和金属离子形成了配价键。游离中性磷化合物，混合有机相中及协萃络合物中的P＝0伸展振动波数与其诱导效应指数之间符合线性规律。将中性磷化合物单独萃取Nd(III)及Er(III)时的分配比，协萃体系的总分配比，酸性协萃系数，表现协萃平衡常数及有机相加合反应平衡常数的对数对P＝0伸展振动频率及诱导效应指数作用，也能找到近似的线性规律。分析环烷酸和PMBP混合前后的振动光谱及换磷共根~1H谱发现环烷酸和PMBP之间也有氢键律合作用。为了进一步说明协萃剂在萃取过程中的作用，合成了除Pm以外十五个稀土－PMRP－环烷酸三元络合物。用快原子轰出质谱法测定了La、Pr及Er等元素络合物的分子量。络合物TG－DTA曲线表明分解过程分两步进行，第一步为环烷酸的分解，第二步为PMBP的分解，最后产物为氧化物。环烷酸首先分解是由于环烷酸和稀土离子的键合强度不如PMBP，这在络合物的质谱，~1HNMR谱及恒温产物的红外光谱中均得到了证实，系统地研究了络合物在4000－100cm~(-1)范围内的FT－IR艺谱，分析了配体和稀土离子配位前后，COOH，ezo, c…e…c及RE－O等振动附近的变化，指出了配体和稀土离子之间的配位形式可能为：PMBP和稀土离子形成的RE－O键伸展振动频率可分为轻重稀土组，环烷酸和稀土离子之间的RE－O键伸展振频率与稀土离子总轨道角动量之间符合斜“W”规律，为常数和原子序数之间呈现近似“四分组”效应，钇位于Lu前，并接近于Lu。还考察了络合物~1HNMR谱上配体的各种基团质子化学位移，指出络合物可能有两种空间模型。在所形成的化合物中，Ce呈现四价状态为Ce(PMBP)_2A_2，其稳定性大于其他三价稀土离子的络合物。

High-Saturation-Power and High-Speed Ge-on-SOI p-i-n Photodetectors

Ge-on-silicon-on-insulator p-i-n photodetectors were fabricated using an ultralow-temperature Ge buffer by ultrahigh-vacuum chemical vapor deposition. For a detector of 70-mu m diameter, the 1-dB small-signal compression power was about 110.5 mW. The 3-dB bandwidth at 3-V reverse bias was 13.4 GHz.

PASSIVATION OF COPPER BY LITHIUM IN P-TYPE GAAS

We report the passivation of two deep copper-related acceptor levels in Cu-diffused p-type GaAs by the group-I element lithium. The deep-level-transient-spectroscopy (DLTS) signals of the well-known Cu-related levels with apparent activation energies 0.15 eV and 0.40 eV disappear in Cu-diffused samples when they are diffused with Li, but can be reactivated by annealing. Photoluminescence measurements show a corresponding disappearance and reappearance of the copper-related luminescence at 1.36 eV. Also we observe with DLT'S an energy level at E(V) + 0.32 eV in the Cu-Li-diff-used samples. The level is neither present in the Cu-diffused samples before Li diffusion nor in Cu-Li-diffused samples after annealing. As the level is not observed in starting materials or solely Li-diffused samples we suggest that it is related to a Cu-Li complex.

RADIATIVE RECOMBINATION IN N-TYPE AND P-TYPE GAAS COMPENSATED WITH LI

We report fundamental changes of the radiative recombination in a wide range of n-type and p-type GaAs after diffusion with the group-I element Li. These optical properties are found to be a bulk property and closely related to the electrical conductivity of the samples. In the Li-doped samples the radiative recombination is characterized by emissions with excitation-dependent peak positions which shift to lower energies with increasing degree of compensation and concentration of Li. These properties are shown to be in qualitative agreement with fluctuations of the electrostatic potential in strongly compensated systems. For Li-diffusion temperatures above 700-800-degrees-C semi-insulating conditions with electrical resistivity exceeding 10(7) OMEGA cm are obtained for all conducting starting materials. In this heavy Li-doping regime, the simple model of fluctuating potentials is shown to be inadequate for explaining the. experimental observations unless the number of charged impurities is reduced through complexing with Li. For samples doped with low concentrations of Li, on the other hand, the photoluminescence properties are found to be characteristic of impurity-related emissions.

LITHIUM PASSIVATION OF ZN AND CD ACCEPTORS IN P-TYPE GAAS

We report lithium passivation of the shallow acceptors Zn and Cd in p-type GaAs which we attribute to the formation of neutral Li-Zn and Li-Cd complexes. Similar to hydrogen, another group-I element, lithium strongly reduces the concentration of free holes when introduced into p-type GaAs. The passivation is inferred from an increase of both the hole mobility and the resisitivity throughout the bulk of the sample. It is observed most clearly for Li concentrations comparable to the shallow-acceptor concentration. In addition, compensation of shallow acceptors by randomly distributed donors is present in varying degree in the Li-diffused samples. Unlike hydrogenation of n-type GaAs, Li doping shows no evidence of neutralizing shallow donors in GaAs.

PHOTOEMISSION-STUDY ON THE SNO2/P A-SICX-H INTERFACE

Ultraviolet and X-ray photoemission spectroscopies (UPS and XPS) have been employed to SnO2 and its interface with P-type a-SiCx:H. The HeI valence band spectra of SnO2 show that the valence band maximum (VBM) shifts from 4.7 eV to 3.6 eV below the Fermi level (E(F)), and the valence band tail (VBT) extends up to the E(F), as a consequence of H-plasma treatments. The work function difference between SnO2 and P a-SiCx:H is found to decrease from 0.98 eV to 0.15 eV, owing to the increase of the work function of the treated SnO2. The reduction of SnO2 to metallic Sn is also observed by XPS profiling, and it is found that this leads to a wider interfacial region between the treated SnO2 and the successive growth of P a-SiCx:H.

A NEW RESULT IN TRANSIENT CURRENT EXPERIMENT ON A-SI-H P/I/N AND N/I/N DEVICES

The transient current response of a-Si:H in both p/i/n and n/i/n structures has been measured as a function of pulse intermittence and pulse amplitude. The results are consistent with the picture that in p/i/n samples the peculiar current response is caused by the competing contributions of electrons and holes which show themselves in different time scales.

SPECTROSCOPIC INVESTIGATION OF HYDROGEN-DOPANT COMPLEXES IN BULK P-TYPE AND IMPLANTED N-TYPE CRYSTALLINE SILICON

Infrared absorption experiments have been performed on hydrogenated and deuterated bulk boron- and aluminum-doped-Si and implanted P, As, and Sb donors in silicon. A first evidence of complex formation in bulk p-type Si is obtained and the spectra confirm the anomalous 3.3-cm-1 deuterium frequency shift with respect to boron isotopes. The ratio of the D-B-11 and D-B-10 peak areas is found to be the same as that of the two boron isotopes natural abundance. In donor-implanted silicon, a quantitative analysis of the obtained data has allowed a rough estimate of the passivating rate due to diffusing deuterium. While the frequencies of the various vibrational lines are found to be in agreement with those reported in the literature, the data on the broad line at 1660 cm-1 (H) or 1220 cm-1 (D) seem to suggest an assignment of this peak to a complex in the bulk involving some type of defect due to the implantation process.