Superlattices and Microstructures最新文献

In the present work, we have concentrated on the structural, electronic, and optical properties of single-layer phase MgCl₂. When bulk MgCl₂ reduces to monolayer form, then it exhibited indirect to direct bandgap transformation. The result indicates that the monolayer MgCl₂ exhibits insulating characteristics with a direct bandgap of 7.377 eV whereas its bulk form has an indirect bandgap of 7.02 eV. It means that when reducing the dimensionally of the MgCl₂ materials than its bandgap significantly increased. The optical properties of the monolayer MgCl₂ have been investigated using DFT within the random phase approximation. The calculated refractive index values are very near to water, which means that monolayer MgCl₂ material will be a transparent material. Also, the optical absorption coefficient is found to be very high in the ultraviolet (UV) region. From optical properties, the out-of-plane (E⊥Z) direction of polarizations is shifted towards the higher photon energy as compared to the in-plane (E||X) direction. From the optical properties profile, the polarizations along in-plane and out-of-plane are different therefore it shows anisotropic behavior. These investigated results show the monolayer MgCl₂ could be a promising material for optoelectronic nanodevices such as deep UV emitters and detectors, electrical insulators, atomically thin coating materials.

In this work, we proposed a switchable metasurface based on phase transmission material of vanadium dioxide (VO₂) with metal and insulation mode. Simulation results demonstrated that the metasurface can switch perfectly at frequencies of 1.89 THz and 2.67 THz from two perfect absorbing peaks to a reflecting peak and a transmitting peak. When VO₂ serves as metal mode, there were two absorption peaks of 99.93% and 99.92% respectively. When VO₂ serves as insulation mode, the reflection and transmission magnitudes were 92.50% and 90.50% respectively. Simultaneously, the structure was insensitive to the incident angle from the simulation result. The proposed metasurface could therefore provide potential application prospects for the terahertz band switcher or sensor.

This work reports on structural, electrical, optical, and photosensing properties of La and Zn co-doped CdO thin films. The co-doped CdO thin films were prepared on glass substrates using the nebulizer spray method at 350 °C. From the structural analysis, a decrease in the crystallite size from 20 to 16 nm is observed against the incorporation of La in CdO:Zn. Inclusion of La in CdO:Zn has also changed the surface morphology with a reduction in the roughness of the thin film samples. EDX analysis confirmed the incorporation of La with CdO: Zn in the prepared films. The bandgap value of the prepared samples increased with the increase in La concentration. A 1.5 wt% of La co-doped with CdO:Zn thin film sample produces low resistivity of 6.81 × 10^-4 Ωcm and a better figure of merit of 8.4 × 10 ⁻⁴ Ω^-1. Finally, the fabricated photodetector with 1.5 wt% of La co-doped with CdO:Zn thin film shows a higher photocurrent and an ideality factor value of 3.4. The photosensing properties of the fabricated (p-Si/CdO–Zn–La (1.5%)) photodetector shows a higher responsivity (R) value of 1.18 AW^-1, specific detectivity (D*) value of 4.90 × 10⁹ Jones, and external quantum efficiency (EQE) value of 274% with 3.0 mW/cm² light intensity. The switching characteristics of the photodetector show a faster rise time (2.9s) and fall time (3.6s) suggesting the fabricated device suitable for photosensing applications.

This paper presents the compact analytical model of underlap gate stack (GS) graded channel (GC) junction accumulation mode (JAM) junctionless (JL) FET. At first, a comparative analysis between the two different graded channel schemes and non-graded channel is performed based on I_ON, I_OFF and I_ON/I_OFF ratio. The scheme that yields the higher I_ON/I_OFF ratio along with smaller I_OFF, is adopted in the proposed JL FET for further analysis. The 2D analytical modeling of the GS-GC-JAM-JL FET deals with the determination of surface potential, threshold voltage, subthreshold drain current, DIBL and subthreshold swing. Results obtained from analytical model and simulations are compared and an excellent match is found. Thus the present paper establishes the outstanding ability of proposed underlap GS-GC-JAM-JL FET architecture to shield the short channel effects without sacrificing its performance, and therefore, proves it as a potential candidate for ultra-low power applications.

In semiconductor industry, at nanoscale dimensions, numerous field effect devices have been proposed and investigated for further improvement in performance of low power circuit and system. In the present research report, a novel low power FET device structure namely: Surrounding Gate Triple Material Heterojunction Tunnel Field Effect Transistor (SGTM-heTFET) has been proposed with the analytical modeling approach. The benefits of surrounding gate and tunnel FETs are coupled to create a new structure, to decrease short channel effects. Three different gate materials with different work functions replace the gate material that surrounds the device. An analytical model of surface potential(ψ), electric field(E) and drain current (I_DS) have been developed for SGTM-heTFET. With the use of low work function material such as 4.0eV, 4.6eV and 4.0eV, the proposed model shows a better ON current of 10⁻⁵ A/μm for a V_GS of 0.7V, ON-OFF ratio of 10¹⁰ with the sub-threshold swing of 50mV/dec. The developed model's for SGTM-heTFET shows excellent device characteristics and have been verified using TCAD simulation, ensuring the model's accuracy.

In this work, the electronic and optical properties of a Nitrogen (N) or a Boron (B) doped BeO monolayer are investigated in the framework of density functional theory. It is known that the band gap of a BeO monolayer is large leading to poor material for optoelectronic devices in a wide range of energy. Using N or B dopant atoms, we find that the band gap can be tuned and the optical properties can be improved. In the N(B)-doped BeO monolayer, the Fermi energy slightly crosses the valence (conduction) band forming a degenerate semiconductor structure. The N or B atoms thus generate new states around the Fermi energy increasing the optical conductivity in the visible light region. Furthermore, the influences of dopant atoms on the electronic structure, the stability, the dispersion energy, the density of states, and optical properties such as the plasmon frequency, the excitation spectra, the dielectric functions, the static dielectric constant, and the electron energy loss function are discussed for different directions of polarizations for the incoming electric field.

Development of decidedly sensitive and selective gas sensors is desirable to maintain control of environment quality against hazardous pollutant. The adsorption of H₂S and SO₂ molecules on pristine and Zn doped MoSe₂ structures is examined by first principles computations - density functional theory (DFT). The work involves analysis of adsorption energy and distance, charge transferred between a structure and a gas molecule, band structure, and density of states (DOS). The band structure of MoSe₂ reveals substantial variations of its electronic properties upon doping with Zn. Furthermore, new bands have been developed near the Fermi level within the DOS due to Zn doping of MoSe₂ structure. The adsorption of both H₂S and SO₂ gases on Zn–MoSe₂ structure is greatly enhanced, as compared with the pristine structure. The Zn-modified MoSe₂ structure exhibits larger adsorption energy for H₂S gas, hence, better sensitivity is comparison with SO₂ gas. This work illustrates that Zn doping of MoSe₂ structure may be considered for sensitive detection of H₂S gas.