Photoelectric characteristics of silicon carbide–silicon structures grown by the atomic substitution method in a silicon crystal lattice

Data obtained in an experimental study of the photoelectric characteristics of silicon–silicon carbide structures grown by the atomic substitution method on silicon (100) and (111) substrates are presented. It is found that the maximum sunlight conversion efficiency of a silicon–silicon carbide (silicon carbide–silicon) heterojunction is 5.4%. The theory of dilatation dipole formation upon synthesis by the atomic substitution method is used to account for the mechanism of electrical barrier formation at the silicon–silicon carbide interface.     

Abnormal solidification of Bi–Te alloys induced by liquid structural states

In this paper, Bi-60 wt.%Te and Bi-80 wt.%Te alloys are selected for experiments to explore the effects of temperature-induced discontinuous liquid–liquid structure transitions TI-LLST on the solidification behaviors and solidified microstructures. Anomalous changes of electrical resistivity of the liquid Bi-60 wt.%Te and Bi-80 wt.%Te alloys with temperature suggested that TI-LLST occurred within 798–828 and 745–779 °C. The solidification results show that solidification behaviors and solidified microstructures of Bi–Te alloys will be apparently distinct when the melt is prepared above the critical temperature. It is found that the nucleation undercooling is larger when the melt experienced the TI-LLST, which leads to finer solidification microstructures.     

Calculation of the Schottky barrier and current–voltage characteristics of metal–alloy structures based on silicon carbide

A simple but nonlinear model of the defect density at a metal–semiconductor interface, when a Schottky barrier is formed by surface defects states localized at the interface, is developed. It is shown that taking the nonlinear dependence of the Fermi level on the defect density into account leads to a Schottky barrier increase by 15–25%. The calculated barrier heights are used to analyze the current–voltage characteristics of n-M/p-(SiC)_1–x(AlN)_x structures. The results of calculations are compared to experimental data.     

3-D simulation of angled strike heavy-ion induced charge collection in silicon–germanium heterojunction bipolar transistors

This paper presents 3-D simulation of angled strike heavy-ion induced charge collection in domestic silicon-germanium heterojunction bipolar transistors （SiGe HBTs）. 3D damaged model of SiGe HBTs single-event effects （SEE） is built by TCAD simulation tools to research ions angled strike dependence. We select several different strike angles at variously typical ions strike positions. The charge collection mechanism for each terminal is identified based on analysis of the device structure and simulation results. Charge collection induced by angled strike ions presents a complex situation. Whether the location of device ions enters, as long as ions track through the sensitive volume, it will cause vast charge collection. The amount of charge collection of SiGe HBT is not only related to length of ions track in sensitive volume, but also influenced by STI and distance between ions track and electrodes. The simulation model is useful to research the practical applications of SiGe HBTs in space, and provides a theoretical basis for the further radiation hardening.     

Influence of the Germanium content on the amorphization of silicon–germanium alloys during ion implantation

We have studied by transmission electron microscopy the amorphization of silicon–germanium (SiGe) alloys by Ge⁺ implantation. We show that when implanted with the same amorphization dose, the resulting amorphous layers get narrower when the Ge content increases. The experimental results can be simulated using the critical damage energy density model assuming that the amorphization threshold rises linearly with the Ge content from 3 eV/at for pure Si to 5 eV/at for pure Ge. These results and simulations are needed to optimize the fabrication of highly doped regions in SiGe alloys.     

Recent progress in epitaxial growth of III–V quantum-dot lasers on silicon substrate

In the past few decades, numerous high-performance silicon (Si) photonic devices have been demonstrated. Si, as a photonic platform, has received renewed interest in recent years. Efficient Si-based III–V quantum-dot (QDs) lasers have long been a goal for semiconductor scientists because of the incomparable optical properties of III–V compounds. Although the material dissimilarity between III–V material and Si hindered the development of monolithic integrations for over 30 years, considerable breakthroughs happened in the 2000s. In this paper, we review recent progress in the epitaxial growth of various III–V QD lasers on both offcut Si substrate and on-axis Si (001) substrate. In addition, the fundamental challenges in monolithic growth will be explained together with the superior characteristics of QDs.     

Influence of parameters of the semiconductor–dielectric interface on the current of the guard ring of silicon photodiodes

Relationships, which determine requirements for the resistance of the inversion layer for decreasing the influence of the guard ring on the dark current and photodiode noisess and allow obtaining the specified intercoupling coefficient between photosensitive elements in multielement photodiodes, are given. It is shown that dependences of the current of the guard ring on the bias voltage and the charge on the Si–SiO₂ interface in the presence of the inversion layer satisfy the current generation model in the space-charge region of the current. The resistance of the inversion layer increase with an increase in the bias voltage in accordance with the relationship R_u ～ V^1.5.     

Tandem adsorption-photodegradation activity induced by light on NiO-ZnO p–n couple modified silica nanomaterials

Well dispersed mono and coupled NiO, ZnO oxides modified silica, with a narrow size distribution, less than 10 nm, have been synthesized by “one–pot” microemulsion assisted sol–gel procedure. The composites exhibited significantly enhanced tandem adsorption–photodegradation activity for the degradation of Methylene Blue dye over 90% (under UV light) and 97% (under sun light). These highly homogeneous oxides modified silica, with very low content of NiO (0.01÷1.14%) and ZnO (0.09%) oxides dispersed in silica, are generating a size effect that leads to nanomaterials with superior properties like higher specific surface area (308 m² g⁻¹), smaller band-gaps energy (2.5 eV) and, consequently, extended light absorption range from UV to natural light. A synergistic effect of mixed n–type ZnO and p–type NiO oxides incorporated in silica has been noticed on the tandem adsorption and photodegradation process. Several influencing process parameters, such as the material and dye loading, stirring speed, NiO/ZnO ratio and light source on the photodegradation performance of NiO-ZnO modified silica related to Methylene Blue cationic dye, were also investigated.     

A 2.7–6.1 GHz CMOS local oscillator based on frequency multiplication by 3/2

Frequency multiplication by 3/2 is proposed as a means to expand the frequency generation capabilities of a single LC VCO. Fractional frequency multiplication is obtained by cascading a broadband injection locked modulo-two divider and a multiply-by-three circuit based on edge combining. The proposed solution is inductorless, thus very compact. It allows the generation of all frequencies from 2.7 to 6.1 GHz with a performance suitable for cellular standards. It shows a phase noise floor below ?150 dBc/Hz and a spurious level below ?35 dBc. The multiplier by 3/2 consumes 5 mA and the VCO draws 10 mA from a 1.2 V supply. The additional power consumption due to the multiplier trades with the small area penalty and the flexibility of this solution, compared to the use of multiple LC VCOs.     

Modeling the effect of deep traps on the capacitance–voltage characteristics of p-type Si-doped GaAs Schottky diodes grown on high index GaAs substrates

Numerical simulation, using SILVACO-TCAD, is carried out to explain experimentally observed effects of different types of deep levels on the capacitance–voltage characteristics of p-type Si-doped GaAs Schottky diodes grown on high index GaAs substrates. Two diodes were grown on (311)A and (211)A oriented GaAs substrates using Molecular Beam Epitaxy (MBE). Although, deep levels were observed in both structures, the measured capacitance–voltage characteristics show a negative differential capacitance (NDC) for the (311)A diodes, while the (211)A devices display a usual behaviour. The NDC is related to the nature and spatial distribution of the deep levels, which are characterized by the Deep Level Transient Spectroscopy (DLTS) technique. In the (311)A structure only majority deep levels (hole traps) were observed while both majority and minority deep levels were present in the (211)A diodes. The simulation, which calculates the capacitance–voltage characteristics in the absence and presence of different types of deep levels, agrees well with the experimentally observed behaviour.     

Specific features of photoelectric and optical properties of amorphous hydrogenated silicon films produced by plasmochemical deposition from monosilane–hydrogen mixture

Photoelectric and optical properties of amorphous hydrogenated silicon films produced by plasmochemical deposition from a monosilane-hydrogen mixture have been studied at a fraction of hydrogen in the mixture that corresponds to the onset of formation of a nanocrystalline phase in the structure of the films obtained. A behavior untypical of amorphous hydrogenated silicon films is observed for the photoconductivity and the spectral dependence of the absorption coefficient. The temperature dependences of the photoconductivity in the films under study are found to vary with the energy of incident photons. At a photon energy of 1.3 eV, temperature quenching of photoconductivity is observed. Prolonged illumination of the films led to a certain decrease in the absorption coefficient at photon energies in the range 1.2–1.5 eV. The results obtained are attributed to the possible presence of silicon nanocrystals in the structure of the films and to the influence of these nanocrystals on their photoelectric and optical properties.     

Time effect of annealing on phase transformations of Cu–Al–Cr nano-ferrites prepared by a co-precipitation method

Amounts of the as-prepared CuAl_0.6Cr_0.2Fe_1.2O₄ nanoparticles by the co-precipitation method have been annealed for different time t for each amount at 800 °C. The samples were characterized using XRD, IR and Mössbauer spectroscopy. The structure of the nanoparticles was transformed from cubic-to-tetragonal-to-cubic with the increase in t. This transformation was assigned to the Jahn–Teller effect (JTE) of Cu²⁺ ions. The transformation process from cubic to tetragonal occurred at annealing time 12 h, whereas the transformation from tetragonal-to-cubic occurred at t≥16 h. The crystallite size, lattice parameters, IR band positions and intensities, force constants, threshold frequency, Debye temperature and stiffness constant were affected by JTE and showed dependence on t. The Mössbauer spectra and parameters confirmed the transformation process by JTE and showed dependence on t. This study confirmed that the increase of annealing time can leads to moving the metallic ions between the crystal sublattices against their site preference and increasing the inversion of cation distributions.     

Effects of Al doping on properties of xAl–3%In–TiO2 photocatalyst prepared by a sol–gel method

A sol–gel method was used to prepare Al–In co-doped TiO₂ photocatalyst. The materials were characterized by XRD, FT–IR, XPS, and N₂ adsorption–desorption measurements. Photocatalytic degradation of methyl orange on the materials was investigated. The diffraction peaks of all the samples are in accordance to the diffraction peaks of anatase phase TiO₂. The addition of Al and In can lead to crystallite size shrinking of anatase TiO₂ in xAl–3%In–TiO₂. The incorporation of Al³⁺ ions into TiO₂ crystal are in the way of substituting Ti⁴⁺ ions in anatase lattice. 0.5%Al–3%In–TiO₂ has the maximum specific surface area of 108.9 m²/g and the smallest average pore size of 7.0 nm. The aluminum doped xAl–3%In–TiO₂ materials have larger adsorption capacity than that of 3%In–TiO₂. Total decoloration efficiency increases gradually with increasing Al content up to 0.5%, while 0.5%Al–3%In–TiO₂ has the maximal decoloration efficiency. 0.5%Al–3%In–TiO₂ also shows much improved activity as compared to 3%In–TiO₂ in each reuse cycle.     

J–V Characteristic of p–n Structure Formed on n-GaAs Surface by Ar+ Ion Beam

Semiconductors - A highly defective ~10-nm-thick layer was fabricated in a high vacuum by 2.5 keV Ar+ ion bombardment of the n-GaAs surface. Valence band photoelectron spectra showed a p-type...     

Effect of Eosin Y Dye on Electrical Properties of ZnO Film Synthesized by Sol–Gel Technique

This paper presents preparation of zinc oxide (ZnO) nanoparticles by the sol–gel technique. ZnO films were prepared by the doctor-blade method, and the resulting films were sensitized with eosin Y (EY) by immersing them in a solution of EY dye in ethanol. The prepared samples were characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transmission infrared spectroscopy, and ultraviolet (UV)–visible spectroscopy. The monodispersed ZnO nanocrystals possess a wurtzite hexagonal structure with diameter of ～7 nm to 17 nm as observed by XRD and TEM analyses. The absorption spectrum of EY-dye-sensitized ZnO (ZnO/EY) film is slightly broadened, with a red-shift in the peak position compared with the absorbance spectrum of the dye in ethanol. Measurements of electrical parameters such as dark conductivity and photoconductivity were carried out at different temperatures. Transient photoconductivity was also studied at different temperatures to investigate the photoconduction mechanism. The photosensitivity of the ZnO/EY film is higher than that of the ZnO film. Hall measurements show n-type behavior for both samples. The visible absorption spectrum and high photosensitivity of the ZnO/EY films support their potential use as photoanode materials in dye-sensitized solar cells and optoelectronic devices.     

Effect of Heat Treatment on the Thermoelectric Properties of Bismuth–Antimony–Telluride Prepared by Mechanical Deformation and Mechanical Alloying

In this work, p-type 20%Bi₂Te₃–80%Sb₂Te₃ bulk thermoelectric (TE) materials were prepared by mechanical deformation (MD) of pre-melted ingot and by mechanical alloying (MA) of elemental Bi, Sb, and Te granules followed by cold-pressing. The dependence on annealing time of changes of microstructure and TE properties of the prepared samples, including Seebeck coefficient, electrical resistivity, thermal conductivity, and figure-of-merit, was investigated. For both samples, saturation of the Seebeck coefficient and electrical resistivity were observed after annealing for 1 h at 380°C. It is suggested that energy stored in samples prepared by both MA and MD facilitated their recrystallization within short annealing times. The 20%Bi₂Te₃–80%Sb₂Te₃ sample prepared by MA followed by heat treatment had higher a Seebeck coefficient and electrical resistivity than specimens fabricated by MD. Maximum figures-of-merit of 3.00 × 10^?3/K and 2.85 × 10^?3/K were achieved for samples prepared by MA and MD, respectively.     

IR photodetectors in the range of λ = 1.5–8 μm, based on silicon with multicharged nanoclusters of manganese atoms

It is demonstrated that infrared photodetectors based on silicon with multicharged nanoclusters of manganese atoms can be designed that operate in the wavelength range of ?? = 1.55?C8 ??m. Photodetectors fabricated on such materials have the following parameters: a spectral sensitivity range of ?? = 1.55?C8 ??m, an operating temperature range of T = 77?C250 K, an optimal electric field of E = 5 V/cm, an optimal size of V = 3 × 2 × 1 mm³, a sensitivity threshold of S = 10^?9 W/cm², and a response time of ?? < 10^?6 s.     

Adhesion improvement of silicon/underfill/polyimide interfaces by UV/ozone treatment and sol–gel derived hybrid layers

Adhesion and mechanical reliability improvement is an important issue for flexible electronics due to weak bonds between silicon/underfill/polyimide interfaces. These interfaces are bonded with weak hydrogen and ester bonds which are vulnerable to humidity. Therefore, in this study, adhesion and reliability of silicon/underfill/polyimide interfaces are enhanced by using UV/Ozone treatment and sol–gel derived hybrid layers. In order to examine the effectiveness of those surface treatment methods, double cantilever beam (DCB) test and subcritical crack growth test were applied to accurately measure the adhesion energy and subcritical crack growth rate. The results showed that the adhesion and reliability against humidity were enhanced by more than 300% and 1000% when both surface treatment methods were applied. Also, the adhesive failure path was altered to mixed mode failure of both cohesive and adhesive failure paths.     

Optical properties of <Emphasis Type="Italic">p–i–n</Emphasis> structures based on amorphous hydrogenated silicon with silicon nanocrystals formed via nanosecond laser annealing

Silicon nanocrystals are formed in the i layers of p–i–n structures based on a-Si:H using pulsed laser annealing. An excimer XeCl laser with a wavelength of 308 nm and a pulse duration of 15 ns is used. The laser fluence is varied from 100 (below the melting threshold) to 250 mJ/cm² (above the threshold). The nanocrystal sizes are estimated by analyzing Raman spectra using the phonon confinement model. The average is from 2.5 to 3.5 nm, depending on the laser-annealing parameters. Current–voltage measurements show that the fabricated p–i–n structures possess diode characteristics. An electroluminescence signal in the infrared (IR) range is detected for the p–i–n structures with Si nanocrystals; the peak position (0.9–1 eV) varies with the laser-annealing parameters. Radiative transitions are presumably related to the nanocrystal–amorphous-matrix interface states. The proposed approach can be used to produce light-emitting diodes on non-refractory substrates.     

Possibility of obtaining the (GaSb)1 − x (Si2) x films on silicon substrates by the method of liquid-phase epitaxy

Semiconductors - It is shown that it is possible to grow a continuous series of (GaSb)1 ? x (Si2) x (x = 0?1) alloys on silicon substrates by the method of liquid-phase epitaxy from a...