Papers by Keyword: Heterostructures

Abstract: Chemical synthesis of nanocomposite particles based on titanium dioxide modified with iron and gold was carried out. It was shown that, depending on the mass content of the doping species, the phase transformation of titanium hydroxide at T = 700 °C proceeds with the formation of either anatase (2 wt.%) or anatase and rutile (8 wt.%). The doping species form a hematite phase and gold clusters on the metal-oxide surface. A weakly crystalline anatase obtained by the transformation of metatitanic acid (MTA), with a particle size of 8 nm and a sulfur content of 0.036%, was selected as the co-catalyst. The anatase co-catalyst exhibits photocatalytic activity in the destruction of organic dyes. Its introduction into the TiO₂&Fe₂O₃&Au nanocomposite suspension promotes the catalytic degradation of cationic and anionic dyes at temperatures ranging from 35 to 60 °C. It was observed that the degradation degree of the solutions after 150 min of catalytic process is the following: Methyl Orange (MO) – 72 %, Methylene Blue (MB) – 71.5 %, Rhodamine B (RhB) – 63.5 %, and Orange G (OG) – 47 %. The reaction rate constant depends on the composition of the dye, varying from 6.5·10^-4 min^-1 for OG to 2.56·10^-3 min^-1 for MB. The prospect of creating heterostructures based on TiO₂ modified with hematite and gold, and their further adaptation for photocatalytic hydrogen production, is considered.

Abstract: Developing materials for electrodes with engineered interfaces is important for improving supercapacitor performance. Combining metal oxides and two-dimensional (2D) transition-metal dichalcogenides (TMDs) is a promising approach to develop enhanced supercapacitor electrodes. To the best of our knowledge, the electrochemical activity and energy storage of the Fe₃O₄/ReS₂ heterostructure-based electrodes have not been reported in the literature. Therefore, this study employed a two-step hydrothermal method to synthesize a Fe₃O₄/ReS₂ heterostructure and investigated its electrochemical performance. The developed material exhibited exceptional specific capacitance, capacity retention, and high energy and power densities. Moreover, various characterization techniques, including SEM, TEM combined with EDX, and XRD, were employed to examine the surface and structural properties of the produced heterostructures. Electrochemical measurements for supercapacitor application were conducted in 2 M KOH electrolytes for all the developed electrodes. The Fe₃O₄/ReS₂ electrode displayed an excellent energy density of 49.31 Wh/Kg, a power density of 550 W/Kg, a specific capacitance of 322.7 F/g, at a current density of 1A/g, and attained 118 % capacitance retention after 2000 cycles at 10 A/g. A specific capacitance of 789.65 F/g was obtained at 5 mV/s. This work uncovers the potential of Fe₃O₄/ReS₂ heterostructures as promising electrode materials for high-performance energy storage applications.

Abstract: The article describes the methods for producing thin films and structures based on SiC, GaN and their SiC – AlN and Al – GaN solid solutions, as well as mathematical models of film growth and properties-behavior of the I–V characteristics of heterostructures. Two models were developed for producing thin films and heterostructures based on SiC, GaN and their solid solutions. The first model makes it possible to determine the sputtering coefficient when producing films by high-frequency magnetron sputtering. In the second quantum-mechanical model, the equation for the gap of the mean field of condensate was built and the growth rate of a film on the crystalline substrate was determined. The current-voltage characteristic of the transistor based on the AlGaN / GaN heterosystem was provided. The models for the growth of heterostructure films made it possible to modify the technologies for producing perfect SiC crystals and SiC – AlN solid solutions. It was possible to offer a pilot plant for growing SiC crystals with improved control over the modes of induction high-temperature heating of the growth crucible.

Abstract: The Indium Gallium Arsenide (InGaAs) based MOSFETs have been widely used in the research of high-speed devices with higher frequency. It has some application in the designing areas of power amplifiers. The InGaAs mainly have greater electron mobility and the lesser band gap in their compound makes them more suitable for developing high-speed devices. The Indium Gallium Arsenide compound-based MOSFETs are designed using the source/drain grown on a passive layer of Indium Phosphide substrate. This helps in reducing the power budget of the MOSFET and thereby reduces source and drain resistance. The re-grown layers over the bulk have serious issues such as parasitic capacitance and greater electrical field at the terminals of the gate along with the drain terminal. This results in a larger leakage current along with the terminals and thereby induces the degradation of the frequency of the application amplifiers. The high-ƙ dielectric along the gate terminal makes the device immune to leakage current for lesser frequency applications. The optimum material for the dielectric may be Hafnium (IV) Oxide – HfO₂ which has been used as a sidewall in the proposed InGaAs MOSFET design. The device simulation was carried out in a way to evaluate the characteristics of the proposed designs. The results were submissive to the conventional MOSFETs in terms of output capacitance over the source and drain terminals, leakage current in the drain terminal, and improved frequency parameters. The results also suggested that the sidewall design over the gate terminal constitutes the frequency improvement without losing the power and current characteristics.

Abstract: A simple route has been developed for the synthesis of Ag₂O/ZnO heterostructures and the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS) and photoluminescence (PL) spectroscopy analysis. Considering the porous structure of Ag₂O/ZnO, the photocatalytic degradation for the organic dyes, such as eosin red (ER), methyl orange (MO), methylene blue (MB) and rhodamine B (RhB), under visible light irradiation was investigated in detail. Noticeably, Ag₂O/ZnO just took 40 min to degrade 96 % MB. The rate of degradation using the Ag₂O/ZnO heterostructures was 2.3 times faster than that of the bare porous ZnO nanospheres under visible light irradiation due to that the recombination of the photogenerated charge was inhibited greatly in the p-type Ag₂O and n-type ZnO semiconductor. So the Ag₂O/ZnO heterostuctures showed the potential application on environmental remediation.

Abstract: The results of the presented studies demonstrate the possibility of using two and three component solid solutions, based on elements of the A3B5 groups, as thin barrier layers to cover an array of structured InAs quantum dots for photoactive heterointerfaces of solar energy. When using three-component solid solutions for QD barrier layers, a decrease in the thermionic generation in the near infrared spectrum and a decrease in the dark current of the heterointerface are obtained.

Abstract: The studies are devoted to the development of the technology of multilayer incorporation of nanocrystals (NCs) of semiconductor chromium and iron disilicides with a layer density no less than 2x10¹⁰ cm-2, the establishment of the growth mechanism of heterostructures with two types of NCs, the determination of their crystalline quality and optical properties, as well as the creation and study of rectification and photoelectric properties of p-i-n diodes based on them. Morphologically smooth heterostructures with 6 embedded layers of CrSi2 nanocrystals and two types of embedded nanocrystals (with 4 layers of CrSi2 NCs and 2 layers of β-FeSi2 NCs) for optical studies and built-in silicon p-i-n diodes were grown for the first time. The possibility of optical identification of interband transitions in embedded nanocrystals in the photon energy range of 1.2 - 2.5 eV was determined from the reflection spectra and the strongest peaks in reflection from the integrated nanocrystals were determined: 2.0 eV for CrSi2 NCs and 1.75 eV for β-FeSi2 NCs. The created p-i-n diodes have a contact potential difference of 0.95 V, regardless of the type of embedded NCs. At 80 K, an absorption band (0.7 - 1.1 eV) was detected in the diodes, which was associated with carrier photo generation in the embedded CrSi2 and β-FeSi2 NCs. From the spectra of the photoresponse at 80 K, the band gap widths in the NCs were determined: 0.50 eV in CrSi2 and 0.70 eV in the superposition of the CrSi2 and β-FeSi2 NCs.

Abstract: During the last decade, silicon carbide (SiC) and its heterostructures with other semiconductors have gained a significant importance for wide range of electronics applications. These structures are highly suitable for high frequency and high power applications in extremely high temperature environments. SiC exists in more than 200 different polycrystalline forms, called polytypes. Among these 200 types, the most prominent polytypes with exceptional physical and electrical attributes are 3C-SiC, 4H-SiC and 6H-SiC. Heterostructures of these SiC polytypes with other conventional semiconductors (like Si, Ge) can give rise to interesting electronic characteristics. In this article, Germanium (Ge) has been used to make heterostructures with 3C-SiC and 4H-SiC using a novel technique called diffusion welding. Microscale and nanoscale simulations of nn-heterojunction of Ge/3C-SiC and Ge/4H-SiC have been done. Microscale devices have been simulated with a commercially available semiconductor device simulator tool called Silvaco TCAD. Whereas nanoscale devices have been simulated with QuantumWise Atomistix Toolkit (ATK) software package. Current-voltage (IV) curves of all simulated devices have been calculated and compared. In nanoscale device, the effects of defects on IV-characteristics due to non-ideal bonding (lattice misplacement) at heterojunction interface have been analyzed. Our simulation results reveal that the proposed heterostructure devices with diffusion welding of wafers are theoretically possible. These simulations are the preparations of our near future physical experiments targeted to fabricate SiC based heterostructure devices using diffusion bonding technique.

Abstract: Neutron degradation of LEDs based upon AlGaInP heterostructures (λ=630 nm and λ=590 nm) with multiple quantum wells are presented in the article. For the initial red LED (λ=630 nm) we can clearly distinguish three characteristic regions. In the small current region a low electron injection mode into the active region of the LEDs is observed. Further, as the operating current goes up, there are average and high electron injection in the active LEDs area regions. However, for the LEDY, the difference in the average and high electron injection regions is more pronounced and low electron injection region is absent. The boundary between the average and high electron injection regions can be characterized by the boundary current, which goes up with increasing exposure level. Three regions of electron injection in the active area of LEDs: low, average and high electron injection are illustrated for both types of LEDs under fast neutron irradiation. Based on the established relationships describing the emission power changing, a phenomenological model of the radiation hardness of LEDs based on AlGaInP heterostructures with MQW was shown. The LEDs radiation hardness is determined by the boundary current value, emission power in the low electron injection into the active LEDs area, the initial defective structure.

Abstract: The electronic structure of nickel iodide monolayer in NiI₂/ScX₂ (X = S, Se and Te) and NiI₂/NiTe₂ heterostructures was investigated by density functional theory (DFT). The spin-asymmetric semiconducting behavior of NiI₂ monolayer in these interfaces was observed. The width of the band gap of the NiI₂ monolayer practically does not change in heterostructures and remains at the level of 1.7 and 3.0 eV for minor and major spin channels, respectively. The NiI₂ layer can be p-doped by stacking with ScX₂ dichalcogenides. On the contrary, charge transfer (~0.01 |e| per f.u.) from NiTe₂ leads to n-doping of NiI₂. As a result, the Fermi level shifts up to the area of NiI₂ conduction band with spin down carriers only, which gives prospects of using this material in spin filter applications. The electronic structure of NiI₂/ScTe₂ under isotropic deformation in the plane remains the same under tension and compression within 5%, except for a small change in the band gap in the composite layers of NiI₂ within 25%. This allows one to conclude about the stability of the electronic properties under deformations, which gives possibility to use the heterostructures in flexible electronics devices.