Specific features of the luminescence and conductivity of zinc selenide on exposure to X-ray and optical excitation

The set of experimental data on the X-ray-excited luminescence and X-ray induced conductivity of ZnSe are compared to the data on the photoluminescence and photoconductivity. It is experimentally established that the current-voltage characteristics and the kinetics of phosphorescence and current relaxation depend on the type of excitation. It is found that the external electric field influences the intensity and shape of bands in the luminescence spectra. It is shown that the character of excitation defines the kinetics of recombination, charge carrier trapping, and conductivity in wide-gap semiconductors.     

Electric-field dependence of linear optical properties in quantum well structures: Waveguide electroabsorption and sum rules

We summarize the electric-field dependence of absorption and luminescence in quantum wells for fields perpendicular to the layers, present extended discussion of electroabsorption spectra and devices in waveguide samples, and derive sum rules for electroabsorption. Optical bistability, self-linearized modulation, and optical level shifting are demonstrated in self-electrooptic effect device configurations, with good modulation contrast and polarization-dependent properties. The electroabsorption spectra enable quantitative comparison of theory and experiment for absorption strengths in quantum wells with field. The sum rules enable excitonic effects to be included in the comparison, and good agreement is seen. One sum rule is also more generally applicable to electroabsorption in semiconductors.     

Effect of coulomb correlations on luminescence and absorption in compensated semiconductors

The spectra of donor–acceptor light absorption and luminescence in lightly doped and lightly compensated semiconductors are calculated. In the photoluminescence calculation, two limiting cases of long and short carrier lifetimes relative to the carrier-energy relaxation time are considered. It is shown that, at long lifetimes, the photoluminescence spectrum is significantly shifted toward longer wavelengths due to the relaxation of minority charge carriers. At intermediate lifetimes, the photoluminescence spectrum consists of two peaks, which is in good agreement with the experimental data.     

Ultrafast luminescence spectroscopy using sum frequency generation

The basic concepts of sum frequency generation are reviewed and its application to the measurement of time-resolved luminescence spectra with subpicosecond time resolution is discussed. The emphasis is on the discussion of those aspects which are important for the optimization of such an upconversion spectrometer. Results of numerical calculations are presented for various nonlinear crystals, and a recently developed upconversion system is reviewed. This system provides excellent time resolution (<400 fs), wide spectral range, large dynamic range, and allows determination of the absolute zero in time delay with high precision. Application of this technique to some problems of current interest in semiconductors is briefly discussed     

Radiative <Emphasis Type="Italic">d–d</Emphasis> transitions at tungsten centers in II–VI semiconductors

The luminescence spectra of W impurity centers in II–VI semiconductors, specifically, ZnSe, CdS, and CdSe, are studied. It is found that, if the electron system of 5d (W) centers is considered instead of the electron system of 3d (Cr) centers, the spectral characteristics of the impurity radiation are substantially changed. The electron transitions are identified in accordance with Tanabe–Sugano diagrams of crystal field theory. With consideration for the specific features of the spectra, it is established that, in the crystals under study, radiative transitions at 5d W centers occur between levels with different spins in the region of a weak crystal field.     

一种利用发光光谱估计LED正向电压的方法

提出了一种通过发光光谱估计发光二极管(LED)正向电压的方法。推导了LED正向电压与结温的关系,探讨了利用发光光谱估计结温的方法,从而建立了发光光谱和正向电压的联系。本文方法不需要直接测量结温和理想因子等参数,只由发光光谱就可得到较为准确的LED正向电压值。实验结果表明,正向电压的光谱估计值和实际测量值能够较好的吻合。     

Direct calculations on the band offsets of large-lattice-mismatched and heterovalent Si and Ⅲ-Ⅴ semiconductors

Band offset in semiconductors is a fundamental physical quantity that determines the performance of optoelectron-ic devices.However,the current method of calculating band offset is difficult to apply directly to the large-lattice-mismatched and heterovalent semiconductors because of the existing electric field and large strain at the interfaces.Here,we proposed a modified method to calculate band offsets for such systems,in which the core energy level shifts caused by heterovalent ef-fects and lattice mismatch are estimated by interface reconstruction and the insertion of unidirectional strain structures as trans-itions,respectively.Taking the Si and Ⅲ-Ⅴ systems as examples,the results have the same accuracy as what is a widely used method for small-lattice-mismatched systems,and are much closer to the experimental values for the large-lattice-mis-matched and heterovalent systems.Furthermore,by systematically studying the heterojunctions of Si and Ⅲ-Ⅴ semiconduct-ors along different directions,it is found that the band offsets of Si/lnAs and Si/lnSb systems in[100],[110]and[111]direc-tions belong to the type I,and could be beneficial for silicon-based luminescence performance.Our study offers a more reli-able and direct method for calculating band offsets of large-lattice-mismatched and heterovalent semiconductors,and could provide theoretical support for the design of the high-performance silicon-based light sources.     

化合物半导体的THz发射光谱

利用反射式太赫兹（THz）辐射产生与探测系统，研究了基于不同半导体的THz发射光谱. 通过快速傅里叶变换，由测得的THz时域光谱得到了其相应的频域光谱，从而对不同半导体的THz发射性质进行了比较. 结果表明，未掺杂的砷化铟(InAs)较其他半导体材料有更高效的THz发射效率.     

Determination of deep levels in semiconductors from C-V measurements

A method is presented that allows deep level density and energy of impurities in semiconductors to be routinely determined from simpleC-Vmeasurements of Schottky barriers. The method is particularly useful for material having levels with very long time constants that are not accessible by noise spectra measurements. The technique is illustrated by measurements of epitaxial n-GaAs which show a donor level at 0.83 eV below the conduction band.     

Influence of supramolecular ordering on photophysical properties of polyamidines

Photosensitive and luminescence properties of some supramolecularly orderable polyamidines are studied. It is shown that the luminescence efficiency of polyamidines, depending on their molecular structure, can more than triply exceed that of widely used organic luminescent semiconductors, i.e., polyphenylenevinylenes. It is assumed that this effect is caused by the fact that polyamidines can form supramolecular structures with π-n-H-conjugation.     

A Novel Approach for the Evaluation of Band Gap Energy in Semiconductors

On the basis of absorption nature of semiconductors, we present a novel and simple method to determine the band gap energies of semiconductors directly from their absorption spectra at any temperatures, without any fitting processes and restrictions of sample thickness. The key point of the approach is the different dependence of the absorption coefficient derivative on the photon energy at different absorption regions in semiconductors. We first demonstrate and verify the approach by detailed temperature-dependent absorption measurements, combined with photoluminescence measurements and empirical band gap equations for the direct band gap of uniform InAs films, and then extend successfully to the indirect band gap of elemental Ge and to the ternary HgCdTe alloys with composition gradient. Furthermore, we have also shown that our approach can not only evaluate the average band gap energy for ternary semiconductor alloys, but also estimate their composition uniformity to monitor the material quality.     

Features of determination of shallow-level impurity concentrations in semiconductors from analysis of the exciton luminescence spectrum

The range of applicability of the method for the determination of the shallow-level donor and acceptor content in semiconductors from the ratio of low-temperature (T=1.8–4.2 K) intensities of exciton-luminescence bands was analyzed; these bands are caused, in particular, by the radiative annihilation of excitons bound to impurities and free excitons. It is shown that the correct data on the concentrations of shallow-level acceptors and donors and on changes in these concentrations under various effects can be obtained if the occupancy of the defects under consideration by electrons and holes is independent of the luminescence excitation intensity and external factors. The procedures for verifying the fulfillment of conditions for applicability of the method are outlined. An example of using the method for determination of thermally stimulated changes in concentrations of shallow-level acceptors and donors in gallium arsenide is given.     

Characterization of defects in colloidal CdSe nanocrystals by the modified thermostimulated luminescence technique

The temperature dependencies of the luminescence spectra of 5-nm-diameter CdSe semiconductor nanocrystals synthesized by colloidal-chemistry methods are investigated. The two bands observed in these spectra around 2.01 and 1.37 eV correspond to band-to-band transitions and luminescence of defect states, respectively. A model explaining the temperature behavior of the luminescence band intensities both upon cooling and heating is put forward. A new modification of spectrally resolved thermostimulated luminescence technique making it possible to determine the activation energies and the character of traps responsible for the temperature dependence of the luminescence intensities is suggested. This technique is used to obtain the activation energies of the emission and capture of electrons at traps (190 and 205 meV, respectively) and to determine the depth of the electron level (57 meV) responsible for luminescence in the 1.37-eV region.     

Study of the vibrational states of CdTe and CdHgTe lattices under conditions of the adsorption of ammonia and carbon dioxide

A comparative analysis of the Raman spectra of CdTe and C_d0.2Hg_0.8Te crystals stored in air, ammonia NH₃, and carbon dioxide CO₂ is performed. It is established that the chemical adsorption of gases causes deformation of the surface of the semiconductors, the signal shape of recombination luminescence varies and hidden vibrational modes of acoustic and optical phonons appear. The variation in the spectrum of lattice vibrations confirms the occurrence of the inverse absorption piezoelectric effect in A ^X B^{8 ? X} materials, particularly CdTe and Cd_0.2Hg_0.8Te.     

硅发光研究进展

硅是间接带隙半导体, 不能有效地发光.量子理论、超晶格理论和纳米技术的发展,给硅基发光研究提供了理论的和技术的支撑.研究者通过不同的途径去实现硅的有效发光:多孔硅、纳米硅、Si/SiO2超晶格、计算化设计与硅晶格匹配的直接带隙半导体.文章报道了这些方面的最新研究进展.     

Microwave measurement of the dielectric constant of high-densitypolyethylene

The method of using interference spectra for determining the dielectric constant, which previously has been developed for semiconductors with dielectric constants of 10-20, has been shown also to yield reliable data for a plastic material, polyethylene, with a dielectric constant of only about 2. Since, for most polymers, the dispersion is very small in the radio-frequency-to-microwave range and the microwave measurement is both very simple and accurate, the interference method may find technical application in material characterization. Prerequisites are a low loss tangent and, hence, good transmission through the thick sample     

应用于白光显示的碲酸盐玻璃上转换发光特性

用高温熔融法制备了Tm3+/Er3+/Yb3+共掺碲酸盐玻璃(TeO2-ZnO-La2O3)样品,测试了玻璃样品的吸收光谱和上转换发光光谱,分析了上转换发光机理。结果发现:在975 nm,波长激光二极管(LD)激励下,制备的碲酸盐玻璃样品可以观察到强烈的红光(662 nm)、绿光(525、546 nm)和蓝光(475 nm)三基色上转换发光,分别对应于Er3+的4F9/2→4I15/2,2H11/2→4I15/2、4S3/2→4I15/2和Tm3+的1G4→3H6能级跃迁;随着Yb3+掺杂含量和泵浦功率的增加,样品的上转换发光强度都得到了一定程度的提高;通过调整稀土掺杂的浓度,得到了接近于标准白光(EE)发射。     

Wide Field Magnetic Luminescence Imaging

This study demonstrates how magnetic‐field‐dependent luminescence from organic films can be used to image the magnetic configuration of an underlying sample. The organic semiconductors tetracene and rubrene exhibit singlet exciton fission, which is a process sensitive to magnetic fields. Here, thin films of these materials were characterized using photoluminescence spectrometry, atomic force microscopy, and photoluminescence magnetometry. The luminescence from these substrate‐bound thin films is imaged to reveal the magnetic configuration of underlying Nd‐Fe‐B magnets. The tendency of rubrene to form amorphous films and produce large changes in photoluminescence under an applied magnetic field makes it more appropriate for magnetic field imaging than tetracene. This demonstration can be extended in the future to allow simple microscopic imaging of magnetic structure.     

Photoluminescence in silicon implanted with erbium ions at an elevated temperature

Photoluminescence spectra of n-type silicon upon implantation with erbium ions at 600°C and oxygen ions at room temperature and subsequent annealings at 1100°C in a chlorine-containing atmosphere have been studied. Depending on the annealing duration, photoluminescence spectra at 80 K are dominated by lines of the Er³⁺ ion or dislocation-related luminescence. The short-wavelength shift of the dislocation-related luminescence line observed at this temperature is due to implantation of erbium ions at an elevated temperature. At room temperature, lines of erbium and dislocation-related luminescence are observed in the spectra, but lines of near-band-edge luminescence predominate.     

Features of the band structure for semiconducting iron, ruthenium, and osmium monosilicides

The pseudopotential method has been used to optimize the crystal lattice and calculate the energy band spectra for iron, ruthenium and, osmium monosilicides. It is found that all these compounds are indirect-gap semiconductors with band gaps of 0.17, 0.22, and 0.50 eV (FeSi, RuSi, and OsSi, respectively). A distinctive feature of their band structure is the “loop of extrema” both in the valence and conduction bands near the center of the cubic Brillouin zone.