Vibronic properties of organic semiconductors based on phthalocyanine complexes with asymmetrically distributed electron density

This study is concerned with the optical properties of organic semiconductors based on lanthanide (III) biphthalocyanine and triphthalocyanine complexes with asymmetrically distributed electron density. The ^ClPcLu^tBuPc biphthalocyanine and ^ClPcEu^BuPcLu^BuPc triphthalocyanine solid films (^ClPc = 2, 3, 9, 10, 16, 17, 23, 24-octachlorophthalocyaninate, ^tBuPc = 2(3), 9(10), 16(17), 23(24)-tetra- tretbutylphthalocyani-nate, ^BuPc = 2, 3, 9, 10, 16, 17, 23, 24-octabutylphthalo cyaninate) are fabricated, and their transmittance spectra in the middle infrared region are studied. Analysis of the transmittance spectra shows that the addition of complexity to phthalocyanine molecules yields some changes in the spectra. Specifically, the isoindole group can exhibit vibronic properties in the form of four absorption lines in the range 1400–1450 cm^-1. New absorption lines that may be due to chlorine-carbon bonds are observed in the far-infrared region.     

Raman scattering in semiconductor structures based on monophthalocyanine and triphthalocyanine molecules incorporating erbium ions

Semiconductor structures of the type of butyl-substituted erbium monophthalocyanine and triphthalocyanine are studied by Raman spectroscopy. It is shown that, when the sandwich-like structure of the molecule incorporating two complexing atoms between the ligands is considered instead of the planar molecular structure with one ligand and one metal atom, a series of lines appears in the Raman spectrum. In this series, the wave numbers of the lines represent an arithmetic progression with the arithmetical ratio ～80 cm^?1. It is suggested that this feature is due to the larger number of organic molecules per metal atom in the triphthalocyanine complex, and the four Raman peaks at the frequencies 122, 208, 280, and 362 cm^?1 are the manifestation of slight out-of-plane vibrations of the phthalocyanine ligands.     

Features of the spectral dependences of transmittance of organic semiconductors based on tert-butyl substituted lutetium phthalocyanine molecules

Vibronic properties of organic semiconductors based on tert-butyl substituted phthalocyanine lutetium diphthalocyanine molecules are studied by IR and Raman spectroscopy. It is shown that substitution of several carbon atoms in initial phthalocyanine (Pc) ligands with ¹³C isotope atoms causes a spectral shift in the main absorption lines attributed to benzene, isoindol, and peripheral C-H groups. A comparison of spectral characteristics showed that the shift can vary from 3 to 1 cm⁻¹.     

Low-threshold defect formation and modification of Ge surface layer under elastic and elastoplastic pulsed laser effects

Changes in the spectra of fluorescence of dye (rhodamine B) molecules adsorbed on a Ge surface and modification of the parameters of Raman and diffuse scattering of light by a semiconductor surface subjected to elastic and elastoplastic effects of pulsed laser radiation are studied. Using contactless photoacoustic measurements based on the laser beam deflection technique, the amplitude of the threshold surface strain is estimated at ～5×10^?5. An appreciable quenching of the fluorescence of the adsorbed probe molecules, an abrupt broadening of the molecular spectra, and an above-threshold increase in the intensity of the diffusively scattered light are observed upon the transition to the range of energy densities corresponding to the inelastic strain formation. The larger the laser-induced strain, the smaller the frequency and the width of the Raman lines, and the higher their intensities. The physical nature of these effects is discussed.     

Optical spectra of microcrystals of the layered semiconductor PbI2 grown in glass matrices

The transmittance, luminescence, and Raman spectra in PbI₂ microcrystals of 2H polytype, grown in the voids of alkali-borosilicate glasses (void dimensions 4–30 nm), are investigated. Depending on the conditions of growth, the exciton states of the microcrystalline systems were found to shift toward higher energies by 35–60 meV relative to the free exciton energy in bulk single crystals as a result of the quantum-well effect. The resonant Raman spectra of PbI₂ microcrystals exhibit not only the conventional Raman component A _1g , but also components associated with the appearance of the E _u and A _2u optical phonons and the two-phonon processes. Fiz. Tekh. Poluprovodn. 32, 151–154 (February 1998)     

Charge transport at the interface of <Emphasis Type="Italic">n</Emphasis>-GaAs (100) with an aqueous HCl solution: Electrochemical impedance spectroscopy study

Charge transport processes at the interface of n-GaAs (100) with an aqueous HCl solution are studied by electrochemical impedance spectroscopy. It is found that when open-circuit potential and anodic potentials are applied to the semiconductor the impedance spectra contain two capacitive semicircles corresponding to the capacitances of the space charge layer and surface states. In the case of open-circuit potential, semiconductor band bending at the interface with the solution is about 0.7 eV and the density of occupied surface states in the dark and under daylight conditions is 1.6 and 2.8 × 10¹² cm² eV⁻¹, respectively. When cathode potentials are applied to GaAs, hydrogen evolution begins at the semiconductor/electrolyte interface and an additional inductive loop appears in the impedance spectra. At the same time, the density of occupied surface states increases considerably both due to a straightening of the semiconductor bands and to the appearance of As-H bonds. Thus, charge transport through the n-GaAs (100)/aqueous HCl solution interface is always mediated by semiconductor surface states.     

Influence of intrinsic point defects on the formation of structural defects and optically active centers during the annealing of erbium-and dysprosium-implanted silicon

The photoluminescence spectra and behavior of the structural defects in layers obtained by implanting 1.0–1.8-MeV Er and Dy ions at a dose of 1×10¹³ cm⁻² are investigated after annealing at 1000–1200 °C for 0.5–1 h in argon or a chlorine-containing atmosphere. The structural defects are studied using transmission electron microscopy and selective chemical etching. The dominant features in the luminescence spectra of the Si:Er and Si:Dy layers following annealing in the chlorine-containing atmosphere are lines associated with the formation of edge dislocations, while the dominant features following the annealing of Si:Er and Si:Dy layers in argon are the erbium-related lines. A comparative analysis of the luminescence spectra of the Si:Er and Si:Dy layers shows that the highest intensity of dislocation-related luminescence is achieved in the erbium-implanted structures. A significant influence of intrinsic point defects on the structural and optical properties of erbium-and dysprosium-implanted silicon is revealed. Fiz. Tekh. Poluprovodn. 33, 656–659 (June 1999)     

Photoluminescence in semiconductor structures based on butyl-substituted erbium phthalocyanine complexes

The study is concerned with the luminescence properties of ensembles of semiconductor structures containing organic phthalocyanine molecules with erbium ions as complexing agents. The photoluminescence spectra of the structures of the type of erbium monophthalocyanine, bisphthalocyanine, and triphthalocyanine are recorded. The photoluminescence peaks are detected at the wavelengths 888, 760, and 708 nm (and photon energies 1.4, 1.6, and 1.75 eV) corresponding to electronic transitions within the organic complexes. It is found that, when a metal complexing agent is introduced into the molecular structure of the ligand, the 708 nm luminescence peak becomes unobservable. It is shown that, in the bisphthalocyanine samples, the photoluminescence signal corresponding to transitions from the 4F _9/2 level of erbium ions is enhanced.     

The Investigation of Property of Radiation and Absorbed of Infrared Lights of the Biological Tissues

The properties of absorption of infrared light for collagen, hemoglobin, bivine serum albumen (BSA) protein molecules with α- helix structure and water in the living systems as well as the infrared transmission spectra for person’s skins and finger hands of human body in the region of 400–4000 cm⁻¹ (i.e., wavelengths of 2–20 μm) have been collected and determined by using a Nicolet Nexus 670 FT-IR Spectrometer, a Perkin Elmer GX FT-IR spectrometer, an OMA (optical multichannel analysis) and an infrared probe systems, respectively. The experimental results obtained show that the protein molecules and water can all absorb the infrared lights in the ranges of 600–1900 cm⁻¹ and 2900–3900 cm^−l, but their properties of absorption are somewhat different due to distinctions of their structure and conformation and molecular weight. We know from the transmission spectra of person’s finger hands and skin that the infrared lights with wavelengths of 2 μm–7 μm can not only transmit over the person’s skin and finger hands, but also be absorbed by the above proteins and water in the living systems. Thus, we can conclude from this study that the human beings and animals can absorb the infrared lights with wavelengths of 2 μm–7 μm.     

Low temperature passivation of Si1−xGex alloys by dry high pressure oxidation

Thermal passivation of Si_1−xGe_x using high pressure (70 MPa) oxidation was studied for potential use in MOS-device applications. Alloys of CVD-grown Si_1−xGe_x (x = 10 and 15 at.%, 200 and 150 nm thick, respectively), were oxidized at 500 and 550°C using high purity dry oxygen at a pressure of 70 MPa. For comparative purposes, a second set of alloys were oxidized using conventional wet atmospheric pressure oxidation at 800°C. X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, transmission electron microscopy (TEM), and metal-oxide semiconductor capacitance-voltage (C-V) measurements were used to characterize the as-grown oxides. Chemical analysis by XPS confirmed that under high pressure conditions compositionally congruent oxides are grown from these alloys. High resolution TEM and Raman spectroscopy show that the as-grown oxide/semiconductor interface is planar and free of Ge enrichment on a scale of 1-2 monolayers. A midgap interface state density for both the 10 and 15 at.% samples of 1 × 10¹² cm⁻² eV⁻¹ was estimated based on 1 MHz C-V measurement.     

Spatial Localization of Carrier Traps in 4H-SiC MOSFET Devices Using Thermally Stimulated Current

Carrier traps in 4H-SiC metal–oxide–semiconductor (MOS) capacitor and transistor devices were studied using the thermally stimulated current (TSC) method. TSC spectra from p-type MOS capacitors and n-channel MOS field-effect transistors (MOSFETs) indicated the presence of oxide traps with peak emission around 55 K. An additional peak near 80 K was observed due to acceptor activation and hole traps near the interface. The physical location of the traps in the devices was deduced using a localized electric field approach. The density of hole traps contributing to the 80-K peak was separated from the acceptor trap density using a gamma-ray irradiation method. As a result, hole trap density of N _t,hole = 2.08 × 10¹⁵ cm⁻³ at 2 MV/cm gate field and N _t,hole = 2.5 × 10¹⁶ cm⁻³ at 4.5 MV/cm gate field was extracted from the 80-K TSC spectra. Measurements of the source-body n ⁺–p junction suggested the presence of implantation damage in the space-charge region, as well as defect states near the n ⁺ SiC substrate.     

光纤共振喇曼光谱法探测水中超痕量生物分子

水中微量生物分子的探测、识别和控制研究是很重要的课题。采用光纤内共振喇曼光谱法,可以提高喇曼光谱的强度109倍。把少量β胡萝卜素溶于吡啶与水的混合液体,充入空心光纤中构成液芯光纤,用514.5nm,30mW激光激发,获得了浓度为10-7mol/L～10-9mol/L的β胡萝卜素喇曼光谱。该技术为研究水中微量生物分子提供了一种新的实验方法。     

Irradiation damages in electron beam lithography

 The irradiation damages in the electron beam lithography(EBL)to Al-gate MOS capacitors in the ranges of 10—30keV and 10~(-6)—10~(-3)C·cm~(-2) and the effects of annealing on damages at low temperature(<500℃)are given.The research on damages caused by high electron energy(30keV) and ultra-high dosages(10~(-4)—10~(-3) C·cm~(-2))is important and useful to the EBL.The resolution can be improved by high electron energy.Both the EBL with vapor-development and without development are all operated at ultra-high dosages.After irradiations,the concentrations of inter- face states can increase by about one to two orders of magnitude and the flat-band voltages by about a few to more than ten volts.Under constant exposure dosages,the fiat-band voltages are independent of the changes of electron energies in certain energy ranges.Under constant electron energies the concentrations of interface states are independent of the changes of exposure dosages in certain dosage ranges.After annealing,the flat-band voltages can recover the values before the irradiations for energies and dosages in the ranges of 10—30keV and 1×10~(-6)—6×10~(-3)C·cm~(-2) respectively.The interface state concentrations due to the damages of ultra dosages can not be removed completely.     

Structure of DX-like centers in narrow-band IV–VI semiconductors doped with group-III elements

This paper presents a study of the structure of the IR reflectance spectra in the sub-gap region of lead telluride doped with indium and gallium and the Raman spectra in PbTe(In). In the Raman and reflectance spectra of PbTe(In), features are observed at a frequency of ω ₀⋍120 cm⁻¹, whose amplitude sharply increases at temperatures T below the temperature where delayed photoconductivity appears, T _c⋍25 K. A similar feature at a frequency of ω ₀⋍155 cm⁻¹ is also observed in PbTe(Ga), with the amplitude of the feature sharply increasing for T>T _c⋍80 K. An analysis of the resulting data makes it possible to conclude that, in contrast with classical DX centers in III–V semiconductors, the microscopic structure of the impurity centers in the two-electron (DX-like) ground state does not correspond to an impurity atom shifted from a lattice site, whereas the impurity atom is shifted from a lattice site for the metastable one-electron impurity state. Fiz. Tekh. Poluprovodn. 32, 679–683 (June 1998)     

Resonance acceptor states in uniaxially strained semiconductors

The energies and lifetimes of resonance states that arise in a uniaxially strained semiconductor are considered in the framework of the zero-radius potential model. The results obtained can be used directly for A ⁺ states and for the qualitative analysis of the behavior of the ground state of a Coulomb acceptor in a strained semiconductor. Numerical results obtained for Ge and GeSi are presented. The oscillator strengths of optical transitions between the resonance state and the ground state in strained germanium are calculated. Fiz. Tekh. Poluprovodn. 31, 1180–1186 (October 1997)     

Features of an intermetallic <Emphasis Type="Italic">n</Emphasis>-ZrNiSn semiconductor heavily doped with atoms of rare-earth metals

The crystal structure, density of electron states, electron transport, and magnetic characteristics of an intermetallic n-ZrNiSn semiconductor heavily doped with atoms of rare-earth metals (R) have been studied in the ranges of temperatures 1.5–400 K, concentrations of rare-earth metal 9.5 × 10¹⁹–9.5 × 10²¹ cm⁻³, and magnetic fields H ≤ 15 T. The regions of existence of Zr_{1 − x} R _x NiSn solid solutions are determined, criteria for solubility of atoms of rare-earth metals in ZrNiSn and for the insulator-metal transition are formulated, and the nature of “a priori doping” of ZrNiSn is determined as a result of redistribution of Zr and Ni atoms at the crystallographic sites of Zr. Correlation between the concentration of the R impurity, the amplitude of modulation of the bands of continuous energies, and the degree of occupation of potential wells of small-scale fluctuations with charge carriers is established. The results are discussed in the context of the Shklovskii-éfros model of a heavily doped and compensated semiconductor.     

Excited states of chalcogen ions in germanium

The energy spectra of chalcogen impurities in germanium are studied by photoconductivity, optical absorption, and photoluminescence. The previously found excited states of these impurities are identified. The observed excited states of tellurium (Te⁺) and selenium (Se⁺) ions are shown to be associated with the Γ and L points of the germanium Brillouin zone, respectively. Fiz. Tekh. Poluprovodn. 32, 155–158 (February 1998)     

Dependence of photoluminescence spectra of epitaxial Pb1 ? xEuxTe (0 ≤ x ≤ 0.1) alloy layers on conditions of growth

The photoluminescence spectra of the Pb_{1 − x} Eu _x Te (0 ≤ x ≤ 0.1) alloy are studied at low temperatures. Epitaxial layers were grown by molecular-beam epitaxy at different temperatures. Along with the basic line corresponding to interband radiative recombination, additional emission lines are observed in the low-energy region of the spectra. Some nonuniformities are observed at the sample surface (within an area smaller than 1% of the total surface area). The concentration and size (1–10 μm) of the nonuniformities decrease with increasing temperature of growth. The additional emission lines are attributed to local nonuniformities in the layer. The dependence of the band gap of the Pb_1−x Eu _x Te (0 ≤ x ≤ 0.1) alloy on the composition parameter x is determined at 77.4 K. The dependence is nonlinear and adequately described by the relation E _g [eV] = 0.213 + 4.8x − 18.4x ².     

Photoluminescence of silicon after deposition of polycrystalline diamond films

Low-temperature (5K) photoluminescence of silicon substrates in the range 0.8–1.2 eV is studied before and after deposition of polycrystalline diamond films. The diamond films were deposited in the microwave plasma onto high-purity dislocation-free silicon (with the resitivity ρ ≈ 3 kΩ cm) subjected to mechanical polishing or more delicate chemical and mechanical polishing. The deposition temperature was 750–850°C. In the photoluminescence spectra of the samples with the substrates polished chemically and mechanically, two lines, D ₁ and D ₂, corresponding to the dislocation-related emission are recorded. Generation of dislocations in the substrates is caused by efficient adhesion of the diamond film and, as a result, by internal stresses that relax with the formation of dislocations. The experimental spectra are practically identical to the photoluminescence spectra observed in silicon (ρ ≈ 100 Ω cm) with the density of dislocations ∼10⁴ cm⁻².