Photoluminescence of erbium ions in heterostructures with silicon nanocrystals

Photoluminescence properties of erbium-doped silicon dioxide layers containing silicon nanocrystals with 1.5–4.5 nm average size are investigated. It is found that the intensity and mean lifetime of the Er³⁺-ion photoluminescence depend on the nanocrystal size, optical pump intensity, and temperature. The results obtained are explained both by the effect of the local environment on Er³⁺ ions and by the manifestation of nonradiative deexcitation of ions caused by the transfer of energy back into the solid-state matrix and the Auger processes.     

硅材料外加直流电场诱导的线性电光效应

在直流电场作用下,硅单晶的反演对称性被破坏,从而诱导产生二阶非线性光学效应.主要研究了硅材料在外加直流电场作用下诱导产生的场致线性电光效应.以沿(111)面切割的近本征硅材料为样品,采用平行板电容器结构,通过横向电光调制实验,观测到在不同直流偏压下,电光信号随调制电压而线性增加,且直流偏压越大,电光信号增加的斜率越大....     

Photoluminescence in dense arrays of silicon nanocrystals: the role of the concentration and average size

The computer-assisted Monte Carlo simulation of the photoluminescence kinetics in planar insulator structures with embedded silicon nanocrystals is carried out. In the simulation, the number of nanocrystals in the array was >10⁶. It is shown that, in rather dense arrays, a significant role is played by the processes of energy exchange between neighboring nanocrystals, resulting in the elimination of smaller nanocrystals from the luminescence process and in a noticeable decrease in the integrated luminescence intensity. Nonexponential decay of the luminescence intensity is established. Such character of the decay is attributed to different relaxation processes prevailing at different stages of system’s evolution.     

Trions in silicon nanocrystals in an amorphous hydrogenated silicon matrix

A simple theoretical model of the radiative recombination in amorphous hydrogenated silicon films containing silicon nanocrystals is suggested. This material is used for the fabrication of modern thin-film solar cells. The calculation results are in good agreement with experimental data on the photoluminescence spectra.     

The distribution of an electric field in p-n junctions of silicon edgeless detectors

Development of silicon edgeless detectors started in 2004 and was motivated by preparations for the total elastic and diffractive cross-section measurement (TOTEM) experiment at the Large Hadron Collider (LHC) at CERN. In the context of this experiment, it would be necessary to detect protons scattered at ultimately small angles with respect to the LHC proton beam, which brings about a limitation imposed on the maximum distance between the beam and the sensitive region of the detector. In order to solve this problem, a new type of silicon detector (edgeless detectors) was developed; these detectors have the structure, which controls the distribution of the current near the edge of the p-n junction. In this paper we report the results of studying the distribution of the potential and an electric field in the region of the cut edge in the silicon edgeless detectors; the models, which account for the obtained results, as well as their consistency with current-voltage characteristics of silicon edgeless detectors developed for the TOTEM experiment, are discussed.     

NH3／H2O2溶液腐蚀下多孔硅光致荧光

用光致荧光谱、傅里叶变换红外光谱（ＦＴＩＲ）和扫描电子显微镜（ＳＥＭ）对用阳极氧化法制成的多孔硅层在１％ＮＨ３／Ｈ２Ｏ２溶液中的腐蚀现象进行了研究。红外分析表明，Ｓｉ－Ｏ键和Ｈ－Ｏ键的强度随ＮＨ３／Ｈ２Ｏ２溶液的腐蚀时间的增加而增加，Ｓｉ－Ｈ键强主匠随腐蚀时间增加而减少。光致荧光谱的峰值在腐蚀开始时先下降后上升，半高宽变窄，谱峰的以边明显蓝移。分析研究表明，１％ＮＨ３／Ｈ２Ｏ２溶液对多孔硅层有腐蚀     

Atomistic tight-binding computations of the electronic properties of ZnSe/ZnS core/shell nanocrystals under applied electric field

The effect of applied electric field on the electronic properties of spherical ZnSe/ZnS core/shell nanocrystals of experimentally relevant size is investigated by the atomistic tight-binding theory. Using this model, the calculations show that a range of electronic properties, including the single-particle spectra, atomistic characters, charge densities, excitonic energies, ground-state coulomb energies, overlaps of the electron and hole wave functions and oscillation strengths, all depend on the strengths of the applied electric field. The spatial distributions of the electron and hole wave functions are induced by the applied electric field. The analysis demonstrates a clear manipulation of the electronic properties of ZnSe/ZnS core/shell nanocrystals by introducing and varying the applied electric field strengths. According to the comprehensive investigations, I suppose that these atomistic computations will be of prospective help for experimental works concentrated on the new optoelectronic devices based on the applied electric field.     

Determination of the electric field in a Hall generator under influence of an alternating magnetic field

A method is described to calculate the electric field in a Hall generator under influence of an alternating magnetic field. The problem is divided into two separate problems, the first of which describes the Hall effect while the second gives the behaviour of the eddy currents. Each of these problems can be reduced to an integral equation, which is easily solved on a digital computer. The method is illustrated for a rectangular Hall generator.     

Doping of silicon nanocrystals

Over the last decades silicon nanocrystals (Si NCs) were the subject of an intense research activity, due to their optical and electronic properties. Different experimental approaches were developed to synthesize Si NCs embedded in a dielectric matrix as well as freestanding Si NCs with well-controlled structural and morphological characteristics. Actually, as in the case of bulk semiconductors, the fine tuning of their optical and electronic properties is related to the effective capability to control doping, i.e. incorporation impurity atoms within these nanostructures. Even if Si NCs incorporating both p-type and n-type dopants were successfully synthetized, several fundamental issues need to be understood. First of all, from a structural point of view, it is very hard to obtain information about dopant location with respect to Si NCs surface and core. This uncertainty is related either to the intrinsic limitations of the experimental approaches for the synthesis and for the analysis of doped Si NCs, or to the difficulties in the modeling of these nanostructures. Moreover, from a fundamental point of view, it is not clear if impurity incorporation in Si NCs effectively results in the generation of free charge carriers as in the case of bulk silicon. This review presents an overview of the recent progress in the field, focusing on the latest results related to doping of Si NCs. In particular the problem of thermodynamic stability of impurities into Si NCs and the problem of modulation of electrical properties of Si NCs will be systematically addressed.     

Photoluminescence of anodized silicon carbide

The luminescence of single-crystalline 6H-SiC plates after electrochemical etching has been investigated. The photoluminescence spectrum was found to change strongly after etching; the decay times of separate bands were determined. Just as in the case of silicon, the change in the photoluminescence could be due to the formation of nanostructures. Fiz. Tekh. Poluprovodn. 31, 315–317 (February 1997)     

Wannier-function approach to electron states in superlattices under an electric field

Electron quasi-stationary states in a periodic semiconductor superlattice are calculated, as linear combinations of Wannier-Kohn functions, for different values of an electric field applied along the heterostructure. A comparison with an alternative approach, which is based on the localization of quasi-stationary states, is performed.     

Photoluminescence characterization of ultrahigh purity silicon

When photoluminescence (PL) measurements on silicon are calibrated against an established measurement technique, they become a powerful characterization tool capable of quantitatively identifying impurities. PL is particularly useful for characterizing ultrahigh purity silicon, due to its ability to determine the concentrations of the shallow impurities down to ≈5 × 10¹⁰ atoms-cm⁻³. We have utilized variable temperature Halleffect measurements to calibrate PL measurements made at 4.2 K on ultrahigh purity float-zone silicon, establishing calibration relationships to determine boron, phosphorus, and gallium concentrations. The concentrations range from the low −10¹² atoms-cm^-3 for phosphorus and boron, to 1 × 10¹⁴ atoms-cm⁻³ for boron and 1 × 10¹⁶ atoms-cm⁻³ for phosphorus. The preliminary gallium calibration concentration range is from the high-10¹² to the mid-10¹⁰ atoms-cm³. Previous PL calibrations based on variable temperature Hall-effect measurements have not produced the theoretically expected proportionality between the impurity concentration and the PL line intensities of the transverse-optical phonon-assisted replicas of the impurity bound exciton normalized to the PL line intensity of the free-exciton. By performing the PL measurements at a fixed free-exciton density, we have achieved the theoretically expected proportionality. The experimental methods and an overview of the theory concerning fixed free-exciton con-ditions, the associated Hall-effect analyses, and the PL calibrations are presented.     

Room-temperature optical absorption in the InAs/GaAs quantum-dot superlattice under an electric field

Electroluminescence and absorption spectra of a ten-layer InAs/GaAs quantum dot (QD) superlattice built in a two-section laser with sections of equal length is experimentally studied at room temperature. The thickness of the GaAs spacer layer between InAs QD layers, determined by transmission electron microscopy, is ∼6 nm. In contrast to tunnel-coupled QDs, QD superlattices amplify the optical polarization intensity and waveguide absorption of the TM mode in comparison with the TE mode. It is found that variations in the multimodal periodic spectrum of differential absorption of the QD superlattice structure are strongly linearly dependent on the applied electric field. Differential absorption spectra exhibit the Wannier-Stark effect in the InAs/GaAs QD superlattice, in which, in the presence of an external electric field, coupling of wave functions of miniband electron states is suppressed and a series of discrete levels called the Wannier-Stark ladder states are formed.     

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.     

硅衬底上CdS纳米晶和纳米碳管极化特性的动态电场力显微术观察

在现有的商用原子力显微镜上实现了用动态电场力显微术来研究单个纳米颗粒的极化特性。将AOT（bis(2-ethylhexyl)sulfosuccinate disodium)分子包覆的CdS纳米晶和Au纳米晶共同沉积在n型硅片表面,以分析导电探针对其诱导极化,同时研究了纳米碳管和碳纳米颗粒的不同极化特性,对样品的原位观察表明：其半导体和金属介电特性的差别,CdS,Au粒子呈现较大的极化反差,在同一纳米碳管不同位置也能观察到类似反差。通过比较在半导体和金属粒子上探针对外加交变电场的响应幅度,可以估计纳米半导体纳米粒子的介电常数。     

Spectra of photoluminescence from silicon nanocrystals

The evolution of time-resolved photoluminescence (PL) spectra in Au-doped nanocrystalline silicon films produced by laser ablation has been studied. The PL spectra with a relaxation time of nanoseconds are broad; they lie in the energy range 1.4–3.2 eV with a peak at 2.4–2.8 eV. At the longest times of tens of microseconds, the spectra become narrower, with a peak at 1.6 eV. At intermediate times, two bands are observed: low-energy (1.6 eV) and high-energy, with the peak shifting from 2.7 to 2.1 eV with time increasing. The data are discussed in terms of quantum confinement, dielectric amplification, and manifestation of kinetically coupled electron-hole and exciton subsystems. Ions and atoms of gold passivate dangling bonds on the Si surface and serve as catalysts for the oxidation of nanocrystals. The similarity between recombination processes responsible for the visible PL in oxidized por-Si layers and in the studied Au-doped films is discussed.     

Generation of electromagnetic radiation based on nanotubes under a constant electric field and an electromagnetic wave field

The possible generation of radiation in the millimeter range based on nanotubes by an alternating (rapidly oscillating) electric field under a constant (or nonstationary) electric field is studied. Radiation enhancement is based on a periodic dependence of the current in nanotubes in such electric fields. The results of a mathematical simulation are presented.     

Spinodal decomposition in an electric field

Spinodal decomposition in an electric field has been suggested as a mechanism initiating the phase separation hypothesized for memory switching in amorphous semi conductors. Here, it is shown that density fluctuations lead to a change in free energy which depends on the direction of the electric field and, hence, should cause preferentially oriented precipitation. In addition, the rate of reaction is influenced by the change of polarization with respect to composition, a contribution which is estimated to be the same order of magnitude as the ideal chemical and strain energy contributions.     

Stimulation of negative magnetoresistance by an electric field and light in silicon doped with boron and manganese

It is experimentally ascertained that light stimulates the negative magnetoresistance observed in a high electric field in silicon doped with boron and manganese. The optimum conditions (the electric field, temperature, illumination, and resistivity of the material) for observation of the largest magnitude of negative magnetoresistance in (Si:B):Mn are determined. The dependence of the negative magnetoresistance on the concentration of compensating impurity is established.     

Raman studies of silicon nanocrystals embedded in silicon suboxide layers

Raman spectroscopy is used for the study of SiO _x (x ≈ 1) layers subjected to thermal annealing at the temperatures from 950 to 1200°C to form Si nanocrystals inside the layers. From comparison of the experimental data with the model of spatial confinement of phonons, the volume fractions of the crystalline and amorphous Si phases in the layers are determined. It is established that, as the annealing temperature is increased, the average dimensions of Si nanocrystals increase from 4 to 6.5 nm. This is attributed to the coarsening of nanocrystals due to crystallization of the amorphous Si phase and to the processes of coalescence of neighboring nanocrystals at the highest temperatures of annealing.