Electronic structure and optical properties of the red and yellow mercuric iodides

With the help of the ab initio full-potential linearized augmented plane wave (FPLAPW) method, calculations of the electronic structure and linear optical properties are carried out for red HgI₂ and yellow HgI₂. It is found that the red HgI₂ has a direct gap of 1.22834 eV and the yellow HgI₂ has an indirect gap of 2.11222 eV. For the red HgI₂, the calculated optical spectra are qualitatively in agreement with the experimental data. Furthermore, the origins of the different peaks of ε ₂ (ω ) are discussed. Our calculated anisotropic dielectric function of the red HgI₂ is a nice match with the experimental results. Our calculated results are able to reproduce the overall trend of the experimental reflectivity spectra. Although no comparable experimental and theoretical results are available, clearly, the above proves the reliability of our calculations, suggesting that our calculations should be convincing for the yellow HgI₂. Finally, the different optical properties are discussed.     

A template‐free route for controlled synthesis of dumbbell‐like Sb2S3 microcrystals

Large amounts of dumbbell‐like Sb₂S₃ microcrystals were synthesized via a simple solvothermal treatment method. Various techniques such as x‐ray diffraction (XRD), field‐emission scanning electron microscope (FESEM), high‐resolution transmission electron microscope (HRTEM), selected area electron diffraction (SAED), and photoluminescence spectrometry (PL) have been used to characterize the obtained products. The results showed that the products belong to the orthorhombic Sb₂S₃ phase, and the dumbbell‐like Sb₂S₃ microcrystals were composed by uniform microrods. Besides, the morphologies of Sb₂S₃ microcrystals could be changed from microshperes to dumbbell‐like microcrystals by only adjusting the reaction solvent. The solvent effects are discussed in detail. Furthermore, the PL properties of the obtained Sb₂S₃ microcrystals clearly show shape effects. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Chemical states of GeTe thin-film during structural phase-change by annealing in ultra-high vacuum

The chemical states of GeTe thin film are investigated using high-resolution X-ray photoelectron spectroscopy (HRXPS) with synchrotron radiation, during amorphous to crystalline structural phase transition. As the temperature increases from 250 to 400 °C, we observe the rock-salt crystalline structure and phase with X-ray diffraction (XRD) and transmission electron microscopy (TEM). Spin-orbit splitting of the Ge 3d core-level spectrum clearly appears after annealing at 400 °C for 5 min. However, the binding energy of the Ge 3d_5/2 core-level peak of 29.8 eV does not change in the amorphous to crystalline structural phase transition. In the case of the Te 4d core-level, change in binding energy and peak shapes is also negligible. We assume that the Te atom is fixed at a site between the amorphous and crystalline phases. Although the structural environment of the Ge atoms changes during the structural phase transition, the chemical environment does not.     

光反馈半导体激光器产生低频起伏与高维混沌信号及其演化过程

利用光反馈半导体激光器产生了低频起伏及关联维数为12.2的高维混沌状态. 实验研究了低频起伏到高维混沌的演变过程. 实验表明,当偏置电流I_b <1.03I_th时,随着反馈强度的降低,低频起伏的峰峰值先增大后减小,平均周期一直减小,直至进入稳定状态,但不能转化为混沌. 当偏置电流I_b >1.03I_th时,随着反馈强度的降低,低频起伏的峰峰值一直增大,平均周期一直减小 关键词： 低频起伏 混沌 半导体激光器 反馈     

磁性半导体/磁性d波超导结中的自旋极化输运

通过求解磁性d波超导中的能隙与磁交换能的自恰方程,利用推广的Blonder-Tinkham-Klapwijk 理论研究磁性半导体/磁性d波超导结中自旋极化准粒子输运系数与微分电导. 计算表明： 1) 磁性d波超导结中的磁交换能h₀可导致零偏压电导峰与能隙电导峰劈裂,劈裂的宽度为2h₀;2) 磁性半导体中的磁交换能h_FS可使零偏压电导峰劈裂的峰值变低. 而由能隙电导峰劈裂的两个子峰,当两种磁性材料的磁 关键词： 磁性半导体 磁性d波超导体 自旋极化输运     

中红外下半导体掺杂调制的表面等离子体透射增强效应

理论研究了平面电磁波通过n型重掺GaAs薄膜的透射谱.当GaAs薄膜两表面刻上亚波长的周期性沟槽结构时,透射谱在中红外波段出现了异常的透射增强现象.把这一现象归因于表面等离子体模式和波导模式的耦合.通过优化结构参数可以得到最大的透射效率.此外,发现随着掺杂浓度的升高,透射谱线中的透射峰逐渐向高频方向移动,最优化后透射峰值随掺杂浓度的升高而逐渐降低.这是由于掺杂浓度的改变,导致了不同的等离子体频率和电子碰撞频率,从而影响了激发模式和薄膜对电磁波的吸收. 关键词： 表面等离子体 掺杂半导体 增强透射 掺杂调制     

PbTe/PbSrTe半导体非对称量子阱中的Rashba效应

窄带隙半导体异质结构的自旋效应最近受到了国际上的很大关注.Ⅳ-Ⅵ族半导体具有各向异性和多能谷的特征,因此可以预期Rashba自旋效应在不同取向的Ⅳ-Ⅵ族半导体量子阱结构中存在显著差异.计算了多个取向的Pb_1-ySr_yTe/PbTe/Pb_1-xSr_xTe非对称量子阱中的Rashba分裂能,结果表明［100］取向的PbTe量子阱的Rashba分裂能在阱宽为5.0nm时 关键词： Ⅳ-Ⅵ族半导体 非对称量子阱 Rashba效应 自旋-轨道耦合分裂     

有机红外半导体酞菁铒的掺杂及电学性质研究

对固相合成法制备的有机红外半导体ErPc₂进行了碘掺杂,有效地将ErPc₂的电阻率降低了约3个数量级.研究了本征和碘掺杂有机红外半导体ErPc₂电阻的温度依赖关系,碘的掺杂除显著地降低了ErPc₂材料的电阻外,其电阻的温度特性没有本质的变化,本征和碘掺杂ErPc₂都表现出指数型的电阻温度依赖关系.碘掺杂有效地降低了载流子的热激活能,使更多的载流子得以参与导电,掺杂后指前因子的减小也为降低材料的电阻 关键词： 有机红外半导体 酞菁铒 掺杂 电学性质     

10 Gb/s Reconfigurable Optical Logic Gate Using a Single Hybrid-Integrated SOA-MZI

A novel reconfigurable Boolean device based on a single Mach-Zehnder interferometer with semiconductor optical amplifiers is demonstrated at 10 Gb/s using intensity return-to-zero modulated signals. The experimental results show that the device can be dynamically reconfigured to operate as a logic XOR, AND, OR, and NOT gate using optical switches. By properly adjusting the input powers, an extinction ratio higher than 10 dB may be obtained. The potential of integration of this architecture makes it an interesting approach in photonic computing and optical signal processing.     

Fabrication and characterization of Mn-doped Cu2O thin films grown by RF magnetron sputtering

Two series of Mn-doped Cu₂O diluted-magnetic-semiconductor thin films were prepared by radio-frequency (RF) magnetron sputtering. One is prepared at different deposition temperature with the same Mn doping concentration; the other is deposited at the same temperature but with varying Mn concentration. They were used to find out the ferromagnetic-order zone for the Mn-doped Cu₂O systems. Most of the samples show high (1 1 1) orientation, except low doping concentration (<6 at%). No impurities were found by X-ray diffraction and electron diffraction measurement. The doped Mn ions substituted Cu ions in the Cu₂O lattice and there were about 1.5% cation vacancies. The grains shown in the transmission electron microscopy (TEM) images for all the samples were tiny, i.e. just 5 nm in diameter. A rough phase diagram for the ferromagnetic order existing in the Mn-doped Cu₂O thin films was given with varying Mn doping concentration and deposition temperature.