Fabrication of black multicrystalline silicon surface by nanosecond laser ablation

The optimal regimes for uniform texturing of a multicrystalline silicon (mc-Si) surface by pulsed laser radiation have been determined. The morphology and reflectance spectra of the texturized mc-Si have been studied. The laser-texturized mc-Si samples with reflectance of 2?C3% over a wide spectral region have been produced. The influence of subsequent chemical etching on the reflective properties of the texturized surface has been analyzed.     

Plasmons in the modulated and confined 2DEG: A Raman scattering study

Lateral wire arrays have been fabricated from a single modulation-doped GaAs quantum well employing reactive ion etching. Depending on the etch depth, the two-dimensional electron gas (2DEG) in the well acquires different degrees of modulation up to complete confinement. The different regimes are identified by their unique photoluminescence and Raman spectra. Deep-etched wires show plasmon resonances down to a width of 100nm.     

Investigation of populated InAs/GaAs quantum dots by photoluminescence and photoreflectance

We studied self-assembled InAs/GaAs quantum dots by contrasting photoluminescence and photoreflectance spectra from 10 K to room temperature. The photoluminescence spectral profiles comprise contributions from four equally separated energy levels of InAs quantum dots. The emission profiles involving ground state and excited states have different temperature evolution. Abnormal spectral narrowing occurred above 200 K. In the photoreflectance spectra, major features corresponding to the InAs wetting layer and GaAs layers were observed. Temperature dependences of spectral intensities of these spectral features indicate that they originate from different photon-induced modulation mechanisms. Considering interband transitions of quantum dots were observed in photoluminescence spectra and those of wetting layer were observed in photoreflectance profiles, we propose that quantum dot states of the system are occupied up to the fourth energy level which is below the wetting layer quantum state.     

Computerized setup for double-monochromator photoreflectance spectroscopy

An experimental setup for studying semiconductor structures by photoreflectance spectroscopy is designed. The double-monochromator-based optical scheme of the setup makes it possible to depress uncontrolled heating of the sample and diminishes a bending of the energy bands due to charge carrier photogeneration. Accordingly, the photoreflectance spectra are detected with a minimal influence of the modulating and probe radiations on the sample. With this setup, the room-temperature photoreflectance spectra from GaAs/GaAsP superlattices are taken and the interband transition energies, as well as a potential step in the conduction band of these superlattices, are measured.     

Laser-modulated reflectance of SbSI near Tc

Reflectance modulation spectra of the semiconducting ferroelectric compound SbSI, at wavelengths near the fundamental edge and at temperatures around the phase-transition are reported. Modulation was obtained by the periodical injection of free carriers produced by a laser beam chopped at 10.18 Hz. In order to explain the mechanism of photoreflectance in SbSI, a comparison of the experimental data has been made both with electroreflectance spectra and eith the theoretical curve expected under the assumption of a periodical change of free carriers density.     

Photoreflectance Spectroscopy of Porous Silicon Photonic Crystals

Journal of Russian Laser Research - We study one-dimensional porous silicon photonic crystals by photoreflectance (PR) spectroscopy. We calculate the reflectance and PR spectra by transfer matrix...     

Photoreflectance measurements in GaAs/AlGaAs asymmetric quantum wells

In this work we investigated the optical control of the bidimensional electron gas density in a single asymmetric quantum well using, for the first time, photoreflectance. We performed our measurements at 80 and 300 K as a function of the power density of the pump beam. Under strong illumination, the bidimensional electron gas density is washed out of the quantum well and under a dark condition, it reaches its maximum value. The variation of the optical transitions observed in our photoreflectance spectra was related to the induced changes of the band profile in between these two limiting cases.     

脉冲紫外激光刻蚀聚合物薄膜的发射光谱和形貌学研究

用聚焦的紫外XeCl准分子激光器轰击高分子聚合物薄膜(涤纶薄膜),由OMA系统接收其发射光谱.发现谱线主要为C2的Swan带和CN的红带,并与高压汞灯照射后的聚合物薄膜的发射谱进行了比较,在我们的实验精度内,没有发现区别.实验显示,每个光脉冲能刻蚀掉几分之一到几个微米的薄膜.激光的刻蚀效应存在波长和能量密度两个阈值.对于涤纶薄膜,能量密度的阈值约为40mJ/cm2.同时还作了紫外吸收光谱和SEM照片的分析.     

Comparison between photoluminescence spectroscopy and photoreflectance spectroscopy in CuGaSe2 epilayer

Photoluminescence （PL） spectroscopy and photoreflectance （PR） spectroscopy are very useful techniques for studying the properties of materials. In this paper, the same material of Cu-rich metal-organic vapour phase epitaxy （MOVPE） grown CuGaSe2 layer is investigated in a temperature range from 20 to 300 K to compare these two techniques. Both PL and PR spectra appear red shifted, less intense and broadened. The temperature dependence of interband transitions is studied by using the Manoogian Leclerc equation. The values of the band gap energy at T=0K and the effective phonon temperature are estimated. The temperature dependences of intensities and broadenings of PL and PR spectral lines are also analysed. Based on the results of the comparison, the features and applications of the PL and PR can be shown in detail.     

导电聚合物P3MT的光调制反射谱

本文报道了导电聚合物光调制反射光谱的研究工作。实验观察到聚三甲基噻吩的带间跃迁和与双极化子态有关的跃迁,并且观察了谱结构随掺杂浓度、温度以及调制光强度的变化。实验结果证明,光子能量大于禁带宽度E_g的光可在聚合物分子链中诱导产生双极化子。虽然双极化子可以由光诱导产生,也可以由杂质诱导产生,但它本身是不依赖于诱导方式的聚合物分子链的本征元激发态。荷电的双极化子可受离化杂质的库仑吸引,产生钉扎效应,并使禁闭参数变大。 关键词：     

Features of ion-beam etching of quartz in a chlorine-containing gas medium

The processes of CCl₄ and SiCl₄ decomposition are simulated by determining the thermodynamic characteristics of reactions between a material subjected to etching and a gas medium. The features of ion-beam etching of quartz are investigated for different working media, including chlorine-containing gases (CCl₄ and SiCl₄) and their mixtures with oxygen. The optimal regimes have been revealed, in which the high rates of quartz etching were attained with the use of a Radical M-100 ion-beam source.     

分子组装体的拉曼光谱

分子组装体（ｍｏｌｅｃｕｌａｒａｓｓｅｍｂｌｉｅｓ）是由若干个子体系形成的特殊体系，具有特定的微观组织和结构。如单分子层、膜、囊泡、胶束、介晶相等［１－５］。这种分子组装体的形成是基于分子与分子间的弱相互作用。这种组装体具有复杂的结构和独特的功能。它...     

Interband transitions from the photoreflectance of GaSb/AlSb multiple quantum wells

We have measured the photoreflectance spectra at 77K of two GaSb/AlSb multiple quantum wells. Excellent quantitative agreement has been obtained between the experimental data and a theoretical calculation of inter-subband energies at Λ (GaSb). This agreement extends over the entire energy range where the hole states are confined and the electron states are below the X conduction band minimum of AlSb. This has made it possible to determine a conduction band offset parameter of 0.85 ± 0.08 (before strain) and the strain distribution. Deviations from the agreement beyond this energy range provide evidence for the mixing of the Λ-X states.     

Band bending at the Si(1 1 1)–SiO2 interface induced by low-energy ion bombardment

Experiments employing photoreflectance spectroscopy have uncovered band bending due to electrically active defects at the Si(1 1 1)–SiO₂ interface after sub-keV Ar⁺ ion bombardment. The band bending of about 0.5 eV resembles that for Si(1 0 0)–SiO₂, and both interfaces exhibit two kinetic regimes for the evolution of band bending upon annealing due to defects healing. The healing takes place about an order of magnitude more quickly at the (1 1 1) interface, however, probably because of less fully saturated bonding and higher compressive stress.     

The etching and structural response of Makrofol-N and Makrofol-KG polycarbonate to γ-irradiation

In order to estimate the damage densities produced by γ-rays to Makrofol-N and Makrofol-KG, some structural, optical and etching studies have been performed. It is found that both polymers are insensitive to low γ-doses (up to 10³ krad) but are influenced at higher doses. The changes in etching parameters have been noticed along with the changes in the FTIR and UV–VIS spectra. The results have been discussed on the basis of some basic mechanisms of radiation interactions with organic materials.     

Photoreflectance spectroscopy of GaAs---AlxGa1−xAs quantum wells under hydrostatic pressure

We report the effect of hydrostatic pressure on the photoreflectance spectra derived from the Γ, X and L bands of a GaAs---Al_xGa_1−xAs heterostructure. The pressure dependence of the quantum well transitions and the valence band-offsets are accurately determined.     

Photoreflectance study of InAs ultrathin layer embedded in Si-delta-doped GaAs/AlGaAs quantum wells

Photoreflectance and photoluminescence studies were performed to characterize InAs ultrathin layer embedded in Si-delta-doped GaAs/AlGaAs high electron mobility transistors. These structures were grown by Molecular Beam Epitaxy on (1 0 0) oriented GaAs substrates with different silicon-delta-doped layer densities. Interband energy transitions in the InAs ultrathin layer quantum well were observed below the GaAs band gap in the photoreflectance spectra, and assigned to electron-heavy-hole (E_e-hh) and electron-light-hole (E_e-lh) fundamental transitions. These transitions were shifted to lower energy with increasing silicon-δ-doping density. This effect is in good agreement with our theoretical results based on a self-consistent solution of the coupled Schrödinger and Poisson equations and was explained by increased escape of photogenerated carriers and enhanced Quantum Confined Stark Effect in the Si-delta-doped InAs/GaAs QW. In the photoreflectance spectra, not only the channel well interband energy transitions were observed, but also features associated with the GaAs and AlGaAs bulk layers located at about 1.427 and 1.8 eV, respectively. By analyzing the Franz-Keldysh Oscillations observed in the spectral characteristics of Si-δ-doped samples, we have determined the internal electric field introduced by ionized Si-δ-doped centers. We have observed an increase in the electric field in the InAs ultrathin layer with increasing silicon content. The results are explained in terms of doping dependent ionized impurities densities and surface charges.     

Technology and characterisation of GaAsN/GaAs heterostructures for photodetector applications

The nitrogen-containing conventional A^IIIB^V semiconductor alloys, so-called diluted nitrides (A^IIIB^V-N), have been extensively studied recently. Unusual properties of these materials make them very promising for applications in lasers and very efficient multijunction solar cells. This work presents the technology and properties of undoped GaAs_1-xN_x/GaAs heterostructures used as active regions in the construction of metal-semiconductor-metal (MSM) photodetectors. The atmospheric pressure metal organic vapour phase epitaxy (APMOVPE) was applied for growing MSM test structures. Their structural and optical properties were examined using high resolution X-ray diffraction (HRXRD), photoluminescence (PL), and photoreflectance spectroscopy (PR). Chemical wet etching was applied for forming an active region and a multifinger Schottky metallization was used as MSM contacts. Dark and illuminated current-voltage characteristics were measured. Based on the obtained results, the main detector parameters as responsivity and spectral response were estimated     

Photoreflectance of GaAs doping superlattices

We have performed room-temperature photoreflectance measurements on two GaAs doping superlattices having considerably different built-in potentials (1.2 eV and 85 meV). The first sample exhibits Franz-Keldysh oscillations, the period of the oscillations corresponding to the . A second dc pump beam has been used to change the electron-hole concentration and hence the built-in field. The spectrum of the second sample displays a number of features corresponding to quantized electron and hole states. There is qualitative agreement between experiment and theoretical calculation based on a two-band tight-binding model. In both samples the dependence of the amplitude of the photoreflectance signal on pump chopping frequency yields the minority carrier lifetime.     

云母模板中Cu纳米线的制备及其光学性质研究

利用快重离子辐照的单晶白云母片产生潜径迹,蚀刻得到直径在30—180 nm纳米孔道. 孔道形状依赖于蚀刻时间,蚀刻时间短得到圆柱形孔道,蚀刻时间长得到菱柱形孔道. 从而在云母模板孔道中电化学沉积得到不同直径和形状的Cu纳米线. 通过紫外可见光谱分析,发现铜纳米线的尺寸和形状影响其光学性质. 直径小于60 nm的近似为圆柱状Cu纳米线有一个明显的表面等离子体共振峰和一个微弱的次峰. 随着直径增加,菱柱状的Cu纳米线主峰有明显的红移,次峰逐渐增强. 同时利用扫描电子显微镜、X射线衍射对Cu纳米线的形貌和晶体结构特征进行了表征. 关键词： Cu纳米线 电化学沉积 光学性质 云母模板