Superlattices and Microstructures最新文献

Due to the excellent properties of two-dimensional (2D) magnetic materials, 2D van der Waals magnetic heterostructures have obtained more research in nanoelectronics. In this work, the electronic and magnetic properties in 2D graphyne/VI₃ (γ-GY/VI₃) magnetic heterostructures have been elaborately examined on account of first-principles calculations. As shown by the research results, semiconductor or half-metallic characteristic of VI₃ monolayer in γ-GY/VI₃ heterostructures may be exhibited due to the difference in stacking pattern. Furthermore, the formation of heterostructures significantly enhances the perpendicular magnetic anisotropy (PMA) of VI₃ monolayer. At compressive strains, VI₃ monolayer of γ-GY/VI₃ heterostructure realizes a shift from semiconductor to metal characteristic, and this significantly enhances the electrical conductivity of VI₃ monolayer. Moreover, through shortening the interlayer distance in γ-GY/VI₃ heterostructures, the spin-up half-metallic state appears in VI₃ monolayer. Both compressive strains and interlayer distance can also enhance the interlayer interaction, charge transfer and PMA of γ-GY/VI₃ heterostructure. These tunable electronic properties show that γ-GY/VI₃ heterostructures can become potential alternatives applicable to nanoelectronic and spintronic device design.

Two light-emitting diodes (LEDs) enabled by InGaN/GaN multiple quantum wells (MQWs) with different well layer growth temperatures (WLGTs) were prepared. The dependences of electroluminescence (EL) spectra of these two structures on temperature at various fixed injection currents indicate that, a decreasing WLGT can result in a conversion of the well layer structure from a one-zone structure with better homogeneity in the localization depth into a two-zone structure with different average In contents and different localization depths, due to the increased In content-induced enhanced component fluctuation. The former is inferred from an “inverted-V-shaped” (increasing-decreasing) temperature-dependent behavior of peak energy at all fixed currents; the latter is mainly inferred from an “M-shaped” (increasing-decreasing-increasing-decreasing) temperature-dependent behavior of peak energy at intermediate fixed currents. These explanations also match those given for temperature-dependent behaviors in terms of external quantum efficiency (EQE) of these two LEDs, including “M-shaped” temperature-dependent behaviors of the EQE of LED B at the intermediate fixed currents.

The flexible transverse β-Ga₂O₃ Schottky barrier diode (SBD) was fabricated by transferring the stripped β-Ga₂O₃ single crystal film onto muscovite, and its electrical characteristic under flat and bending conditions were tested. It is found that the forward current of the device after bending increases in the small voltage range of 0–1 V and decreases in the large voltage range of 1–4.5 V as the curvature increases. This result is attributed to the two mechanisms that the barrier height decreases and the scattering increases with the increase of the curvature. The decrease in barrier height makes it easier for electrons to migrate from the cathode to the anode in small voltage range, while the current decreases in large voltage range due to scattering. It is further found that the maximum transconductance (g_m) and subthreshold swing (SS) deteriorate with the increase of curvature and the corresponding voltage value of g_m drifts to the right. In addition, the switch ratio of the device under flat conditions is 10⁸, whereas in bending tests the switch ratio is 10⁷ which is only reduced by one order of magnitude and it is essentially the same as the current level under flat conditions.

The present work is an endeavour to investigate non‒saturation behaviour of reverse current in Ni/SiO₂/p-Si/Al over a wide low temperature range of 70–300 K at step of 10 K using well accepted models i.e., Poole-Frenkel emission, Schottky emission and Fowler‒Nordheim tunneling mechanisms. The results of the study revealed that Schottky emission has the dominance over Poole-Frenkel emission in the temperature range of 200–300 K with the trap state activation energy of 0.17 eV. In the remaining temperature range trap assisted tunnelling and involvement of other mechanisms were suggested. Further, the Fowler‒Nordheim tunneling mechanism was found to be effective above reverse bias of 0.5 V over the entire temperature range of 70–300 K. Thus, variation of barrier height with temperature was examined using Fowler‒Nordheim tunneling model and it was found to increase from 0.17 eV to 0.28 eV as temperature varied from 300 to 70 K. The increase in barrier height with decrease in temperature corroborates the decrease in reverse current with temperature.

This study investigated a numerical study of fluid flow and heat transfer in micro channel with four heat sources that located on upper and lower walls. Four heat sources are located in the upper and lower walls symmetrically respect to centerline. Lattice Boltzmann method is used to solve related equations of flow and temperature of fluids, this method is included two steps such as collision and streaming steps. Reynolds number is varied from 0.1 to 10 and Knudsen number is changed from 0 to 0.1 for air. The slip velocity and temperature jump boundary condition are used for micro channel simulation with Knudsen numbers related to slip velocity flow. Bounce-back boundary conditions were applied on all solid boundaries, which means that incoming boundary populations are equal to out-going populations after the collision. A comparison with other study is done and a good result is gained. The results show that the Knudsen number has important role in heat transfer and the highest mean temperature at outlet occurs at highest Knudsen number and heat transfer convection is more significant for first heat source comparing second heat source.

Electronic and optical properties of Fe-doped MoSe₂ monolayer with (without) N₂O gas adsorption are reported in this paper. The impact of N₂O gas adsorption on both the properties (electronic, optical) is significantly observed as compared to their pristine MoSe2 monolayer (ML) counterpart. The adsorption energy (Eads) is −0.40 eV for N₂O/Fe-doped MoSe₂ ML followed by charge transfer of 8.00e for the electronic property. Similarly, for Fe-doping on MoSe₂ ML a phase transition from semiconducting to metallic (2H →1T) behavior, is displayed from the band structure analysis. Later, after N₂O gas adsorption, semiconducting (2H) behavior is regained due to high electron affinity of Fe-atom, as analyzed from its band structure. Moreover, the work function is modulated from 5.73 eV for pristine MoSe₂ ML, to 4.12 eV for Fe–MoSe₂ ML and 4.06 eV for N₂O/Fe-doped MoSe₂ ML post gas adsorption respectively. Further, the imaginary part (ε₂) of dielectric constant is shifted from 2.38 to 6.83 arbitrary unit (a.u.) from pristine to N₂O/Fe-doped MoSe₂ ML, respectively. Noticeably, the refractive index is altered from 1.54 to 6.6 a.u. while absorption index is varied from 1.07 to 0.00 a.u. showing its potential ability to absorb light in the visible region. Lastly, this nature is again confirmed from orbital and molecular level interaction in total density of states plots. This increases its utility to be used for different photovoltaic applications such as photo detectors and display devices.

In this paper, we stacked graphene, black phosphorus (BP) and a BC₂P monolayer to form one BC₂P/BP and three BC₂P/graphene (-a, -b, -c) vdW heterostructures based on examining the stability of BC₂P monolayer predicted by our group. Firstly, we discussed structures and formed possibilities of four vdW heterostructures by calculating binding energies, elastic constants and plane-averaged differential charge densities respectively, and found they are hard 2D materials even larger than the graphene. Secondly, four vdW heterostructures are direct semiconductors with the band gap as 1.053, 1.525, 0.148 and 1.085 eV under the HSE06 or PBE functional respectively, and have at least a high carrier mobility with the value as ∼10⁴ cm²/V·s or up to ∼10⁵ cm²/V·s. Thirdly, under different in-plane stresses from −6% to 6%, their optical absorption coefficient peaks shift from the ultraviolet light area to the visible light area accordingly, and the BC₂P/BP heterostructure can transfer from a metal to a semiconductor. Additionally, when the strain ratio is −6%, their absorption coefficients can reach up to the largest value respectively, especially the absorption coefficient of BC₂P/BP heterostructure can reach up to the value 29% of incident light. These results make four vdW heterostructures to be well potential materials for the application of photovoltaics and optoelectronics devices.

In this theoretical study, we consider in detail the influence of the confining potential on the magneto-optical absorption linewidth (MOALW) of a quantum well for both intersubband and intrasubband magneto-optical transitions. The projection operator method and the profile technique are used to calculate respectively the MO-absorption power and MOALW in both the semiparabolic, parabolic, and the rectangular confining potential quantum wells. The results obtained from the present study show that (i) the MOALW as functions of the structural, material, and external parameters include the confining potential frequency, the well width, the electron density, the temperature, and the magnetic field, as well as Landau level number; (ii) the larger contribution from intrasubband transitions to electron-phonon scattering compared with intersubband transitions for both three type of above confining potentials; (iii) the dependence of the MOALW on the above parameters is found to be the strongest in case of the square confining potential quantum well while it is the weakest in case of the semiparabolic confining potential quantum well for intersubband magneto-optical transitions, however, that for the parabolic confining potential is similar to the rectangular confining potential for intrasubband magneto-optical transitions. Our present calculations accord well with previous experimental studies.

In this paper, a high extinction ratio (ER) and a low power silicon-plasmonic hybrid electro-optic modulator based on graphene has been proposed and designed. The proposed modulator has three coupled waveguides, two silicon waveguides, and one hybrid plasmonic waveguide. A hybrid plasmonic waveguide has two coupled graphene layers. Two-dimensional hexagonal boron nitride (hBN) and hafnium oxide (HfO₂) are used in the plasmonic waveguide. The high performance and quality modulator is obtained with this combination of materials. By electrically adjusting the graphene refractive index as low as a noble metal, the hybrid plasmonic waveguide support the high lossy surface plasmon polariton (SPPs) waves. Therefore, the propagating optical mode experiences high power attenuation. In addition, the coupling length between waveguides is changed, which causes further attenuation of light. The designed modulator has a high ER (11.01 dB/μm), wide f_3dB modulation bandwidth (72.2 GHz), and low power consumption (19.36 fJ) at 1.55 μm wavelength. The finite-difference time-domain (FDTD) method is used to investigate the proposed modulator characteristics.

The neodymium (Nd) doped indium-zinc-oxide (NIZO) is a material with high mobility and great potential in transparent electronic devices. NIZO thin films were prepared by pulsed laser deposition (PLD) at 250, 350, 450, and 550 mJ/pulse laser energy, respectively. With the increase of laser energy, the films gradually change from an amorphous to an amorphous/crystalline state and the In₂O₃ crystals have preferential growth in the (123) plane. The average transmittance of the film is higher than 80% in the visible range. When the laser energy is 250 mJ, the carrier mobility has the highest value of 14.43 cm² V⁻¹ s⁻¹, and it decreases with the increase of laser energy. The possible reason for this phenomenon is given by electronic structure and crystallization. Based on the content of defect states and the emitted particle number, the carrier concentration of the films is analyzed.