Laser-assisted simulation of transient radiation effects in heterostructure components based on A<Superscript>III</Superscript>B<Superscript>V</Superscript> semiconductor compounds

The possibility of the simulation of transient radiation effects using laser radiation in microwave heterostructure elements based on A^IIIB^V semiconductor compounds is studied. The results of the laser simulation of transient radiation effects in pseudomorphous high-electron mobility transistors (pHEMTs) based on AlGaAs/InGaAs/GaAs heterostructures are reported. It is shown that, for the adequate simulation of transient effects in devices on GaAs substrates, one should use laser radiation with a wavelength of λ = 880–900 nm taking into account the dominant mechanisms of ionization in the transistor regions.     

Cathodoluminescence of laser A<Superscript>II</Superscript>B<Superscript>VI</Superscript> heterostructures

A Cathodoluminescence (CL) method has been used for studies of ZnSe-based heterostructures with a CdSe fractional-monolayer recombination region. Electron beams with energies of 1–25 keV provide the ability to analyze CL bands associated with different layers of the heterostructure and revealed on the CL spectrum at different electron-beam penetration depth. Comparative analysis of the CL bands both from the recombination region and the upper layers has been used to characterize the transport properties of the structure. The correlation between the density and size distribution of quantum dots and full width at half maximum and spectral position of the CL bands has been studied in detail. The text was submitted by the authors in English.     

Molecular state of <Emphasis Type="Italic">A</Emphasis><Superscript>+</Superscript> centers in GaAs/AlGaAs quantum well

Along with the separate A ⁺ centers in the GaAs/AlGaAs quantum wells, there exist paired molecular states of the centers. The molecular states manifest themselves as the second peak of photoluminescence associated with the A ⁺ centers. This statement is based on data on the specific features of circular-polarized photoluminescence and on the characteristic dependences of the amplitudes of photoluminescence peaks on the degree of doping and temperature. The binding energy of holes in the molecular states is determined. It is suggested that the paired state of two positively charged A ⁺ centers is possible due to the polaron effect.     

Influence of Indirect Transitions on Optical Characteristics of A<Subscript>3</Subscript>B<Subscript>5</Subscript> Heteroepitaxial Layers

The influence of indirect transitions of Г-L and Г-Х types in the Brillouin zone on optical and electrophysical characteristics of heteroepitaxial layers of А₃В₅ compounds is estimated by the example of ternary (InGaAs) and quaternary (InGaAsP) compounds. It has been found that consideration of indirect transitions lowers the refractive index of semiconductor compounds by up to 15% in a narrow wavelength range of 0.4—0.6 μm.     

Formation of Precipitates in Si Implanted with <Superscript>64</Superscript>Zn<Superscript>+</Superscript> and <Superscript>16</Superscript>O<Superscript>+</Superscript> Ions

The results of studying the surface Si layer and precipitate formation in CZ n-Si(100) samples sequentially implanted with ⁶⁴Zn⁺ ions with a dose of 5 × 10¹⁶ cm² and energy of 100 keV and ¹⁶O⁺ ions with the same dose but an energy of 33 keV at room temperature so that their projection paths R_p = 70 nm would coincide are presented. The post-implantation samples are annealed for 1 h in an inert Ar medium in the temperature range of 400–900°C with a step of 100°C. The profiles of the implanted impurities are studied by time-of-flight secondary ion mass spectrometry. The Si surface is visualized using a scanning electron microscope, while the near-surface layer is visualized with the help of maps of elements formed by Auger electron spectroscopy with profiling over depth. The ZnO(002) texture is formed in an amorphized Si layer after the implantation of Zn and O ions. ZnO(102) crystallites of 5 nm in size are found in a recrystallized single-crystalline Si layer after annealing in Ar at 700°C.     

Effect of potential fluctuations on the energy structure of GaAs/AlGaAs quantum wells with A<Superscript>+</Superscript> centers

The transformation of photoluminescence spectra associated with A⁺ centers in GaAs/AlGaAs quantum wells due to changes in the pumping level and temperature is analyzed. It is shown that an important part in the formation of the energy structure of the system of GaAs/AlGaAs quantum wells is played by electrostatic potential fluctuations responsible for the spatial redistribution of charge and the appearance of free holes.     

Circular polarization of the photoluminescence from a system of two-dimensional <Emphasis Type="Italic">A</Emphasis><Superscript>+</Superscript> centers in a magnetic field

A series of GaAs/AlGaAs quantum well structures with different concentrations of A ⁺ centers is studied experimentally by polarized photoluminescence spectroscopy. The spectral dependences of the circular polarization and the energy shifts in a magnetic field exhibit qualitatively different behavior for samples corresponding to the weak and strong localization conditions. The results obtained are explained in the context of a suggested model describing optical transitions between states of localized and free electrons and A ⁺ centers.     

Effect of ionic Ag<Superscript>+</Superscript> transfer on localization of metal-assisted etching of silicon surface

The specific features of fabrication of 3D silicon structures via local formation of a sacrificial porous silicon layer by metal-assisted chemical etching with 50- and 100-nm-thick silver films as a catalyst are studied. It is found that the mass transfer of Ag⁺ ions, caused by the temperature gradient, affects the surface morphology of the structure being formed, depending on the linear size of the mask-catalyst.     

<Superscript>63</Superscript>Cu and <Superscript>115</Superscript>In NMR study of CuInS<Subscript>2</Subscript> semiconductor

Two CuInS₂ semiconductor samples synthesized from chemical elements with the equiatomic cation ratio (N _Cu/N _In = 1) and either an excess or stoichiometric sulfur content have been investigated by ⁶³Cu and ¹¹⁵In nuclear magnetic resonance. The spectra were recorded on a Bruker Avance-400 spectrometer at a temperature of 290 K and frequencies of 106.14 MHz (⁶³Cu) and 87.67 MHz (¹¹⁵In). Numerical simulation made it possible to determine the quadrupole coupling constants: 0.34 MHz (⁶³Cu) and 1.1 MHz (¹¹⁵In). For the samples synthesized with excess sulfur (above stoichiometry), distortions are revealed in both the ⁶³Cu and ¹¹⁵In spectra.     

Cathodoluminescence properties of yttrium aluminum garnet doped with Eu<Superscript>2+</Superscript> and Eu<Superscript>3+</Superscript> ions

Yttrium aluminium garnet (YAG) doped with Eu²⁺ and Eu³⁺ ions is very interesting as a phosphor for conversion of light-emitting diode light for white light sources. The europium ion occupies the structural position of yttrium in yttrium aluminium garnet and has valence state Eu³⁺. Our sample was doped with Zr⁴⁺, which is why some of the europium ions had valence state Eu²⁺. As a rule, luminescence of Eu³⁺ ions is observed in the orange and red range of spectrum. The luminescence of Eu²⁺ in yttrium aluminum garnet is characterized by an intensive broad band with maximum of intensity at about 560 nm (green color). In this work, we studied the intensity and decay time dependences on europium concentration, and the influence of excitation power density on the cathodoluminescence of the sample. The most interesting result is the change of visible cathodoluminescence color in dependence on the density of the exciting power. The text was submitted by the authors in English.     

Design of the H<Subscript>10</Subscript><Superscript>□</Superscript> to H<Subscript>01</Subscript><Superscript>°</Superscript> Sector-Type Mode Converter at Ka-Band

A design procedure for the H₁₀^□ to H₀₁^° sector-type mode converter at Ka-band is described in detail. As an example, an H₁₀^□ to H₀₁^° sector-type mode converter with an input rectangular port size as 7.112×3.556 mm² and another output circular port diameter as 17.2 mm is designed and measured for insertion losses and wanted mode pattern. The mode converting efficiency from H₁₀^□ mode to H₀₁^° mode is about 91.2%. The insertion losses of the converter are lower than 0.1525 dB with 2GHz band.     

Electrical properties of isotype <Emphasis Type="Italic">N</Emphasis><Superscript>+</Superscript>-GaSb/n<Superscript>0</Superscript>-GaInAsSb/<Emphasis Type="Italic">N</Emphasis><Superscript>+</Superscript>-GaAlAsSb type-II heterojunctions

Band diagrams and current-voltage and capacitance-voltage characteristics of isotype N ⁺-GaSb/n⁰-GaInAsSb/N ⁺-GaAlAsSb heterostructures have been studied. Dark-current flow mechanisms have been analyzed. It is shown that a staggered type-II heterojunction can behave as a Schottky diode and its current-voltage characteristics exhibit rectifying properties over the entire temperature range 90–300 K. The thermionic-emission current predominates at high temperatures and low voltages. This current is due to thermal excitation of electrons from GaInAsSb to GaSb over the barrier at the heterointerface. A comparison of the relevant theoretical and experimental data confirmed that the tunneling charge transport mechanism plays the key role at low temperatures under both forward and reverse biases.     

Effect of microwave treatment on current flow mechanisms in Au-TiB<Subscript>x</Subscript>-Al-Ti-n<Superscript>+</Superscript>-n-n<Superscript>+</Superscript>-GaN-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> ohmic contacts

The temperature dependences of the contact resistivity ρ_c of Au-TiB_x Al-Ti-n⁺-n-n⁺-GaN-Al₂O₃ ohmic contacts have been studied before and after microwave treatment followed by nine-nonth room-temperature sample storage. The temperature dependences of ρ_c of initial samples were measured twice. The first measurement showed the temperature dependence typical of ohmic contacts; the repeated measurement in the temperature region above 270 K showed a ρ_c increase caused by metallic conductivity. After microwave treatment, the metallic conductivity in the ohmic contact is not observed. This is presumably associated with local heating of metal Ga inclusions under microwave irradiation and the formation, due to high chemical activity of liquid gallium, of compounds of it with other metallization components. In this case, the temperature dependence of ρ_c is controlled by ordinary charge transport mechanisms. After nine-nonth room-temperature storage, the temperature dependence of ?c is described by the tunneling mechanism of charge transport.     

Features of <Superscript>63,65</Superscript>Cu NMR Spectra in the Local Field of Samples of CuFeS<Subscript>2</Subscript> Semiconductor Mineral from Oceanic Sulfide Deposits

The results of studying natural samples of CuFeS₂ chalcopyrite mineral from hydrothermal ore manifestations of island arcs of the Pacific Ocean by ⁶³Cu nuclear magnetic resonance (⁶³Cu NMR) in a local field at room temperature are presented. The asymmetric shape of the detected resonance lines in the ⁶³Cu NMR spectrum indicates the presence of at least two overlapping lines. The presence of two overlapping central components can be a consequence of the occurrence of regions with different types of structural distortion near the resonant nuclei. These results show that the pulsed ⁶³Cu NMR method can be an effective method for studying the physical properties of deep-sea polymetallic sulfides of the global ocean.     

Photosensitivity of thin films of semiconductor nanocomposites based on metal-organic complexes with Cu<Superscript>+</Superscript> and Ru<Superscript>2+</Superscript>

The photosensitivity of nanocomposites in a system constituted by an organic transition metal complex and silica was studied. It is shown that the photosensitivity of a nanocomposite is determined by the valence and the ionization potential of the metal atom, which is equal to (3–8)×10⁴ cm²/J (quantum yield of carrier photogeneration is 0.03–0.05) for the Cu⁺ complex and 5×10³ cm²/J for the Ru²⁺ complex. The possibility of controlling the magnitudes and spectra of both the photosensitivity and luminescence of thin films of nanocomposites based on these complexes by varying the structure of metal complexes and the fact that the quantum efficiency of photogeneration can be raised by introducing transport molecules into the structure of a nanocomposite gives reason to believe that photosensitive and electroluminescent devices can be created on the basis of these nanocomposites.     

Spectroscopic parameters of the absorption bands related to the local vibrational modes of carbon and oxygen impurities in silicon enriched with <Superscript>28</Superscript>Si, <Superscript>29</Superscript>Si,and <Superscript>30</Superscript>Si isotopes

The IR spectra of all three Si isotopes in the form of bulk single crystals (²⁸Si with an enrichment of more than 99.9%, and ²⁹Si and ³⁰Si with an enrichment of more than 90%) have been studied at T = 300, 17, and 5 K in the spectral range 550–1200 cm^?1. The IR active local vibrational modes (LVM) of Si-¹²C centered at 605 cm^?1 and Si-¹⁶O-Si quasi-molecules in the region of 1136 cm^?1 for all the Si isotopes, in comparison with Si possessing a natural isotopic composition, as well as their isotopic shift at 300 and 17 K, have been determined. The dependence of the shape of the antisymmetric stretching vibration band for ²⁸Si-¹⁶O-²⁸Si in the spectrum of ²⁸Si on spectral resolution has been studied. The possibility of generalizing the IR spectroscopy method for the determination of carbon and oxygen impurities in Si possessing a natural isotopic composition to monoisotopic Si have been discussed.     

Digital deep level transient spectroscopy considered for discrimination of traps closely spaced in emission coefficients in semiconductors

A method is presented for analysis of digitally recorded capacitance transients to give activation energies and capture cross-sections of two deep levels which would yield overlapping peaks in conventional DLTS spectra. It is shown that baseline errors can be overcome by proper analysis of the data. The accuracy of the method is examined by simulation with parameters representative of a typical DLTS system. The addition of various noise levels is also simulated and the effects of averaging of transients on the ability to discriminate closely spaced traps is examined quantitatively.     

Excitation of Er<Superscript>3+</Superscript> ions in SiO<Subscript>2</Subscript> with Si nanocrystals

Probabilities of excitation of erbium ions via Coulomb interaction with carriers localized in silicon nanocrystals embedded in SiO₂, in recombination and intraband relaxation of these carriers, have been calculated.     

IR and FIR Spectroscopy of <Superscript>13</Superscript>CH<Subscript>3</Subscript>I

We have investigated the ¹³CH₃I isotopomer of methyl iodide as a source of Far Infrared (FIR) laser radiation using the optical pumping technique. The molecule is pumped by using a pulsed waveguided CO₂ laser, driven by a novel all solid state power supply that lases on the 10HP band as well as the regular bands. We discovered and assigned two new FIR laser emissions and we give further spectroscopic information about polarization and pump frequency offset for five already known lines.