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 x 10(-4) omega cm and a better figure of merit of 8.4 x 10(-4) omega(-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 x 10(9) Jones, and external quantum efficiency (EQE) value of 274% with 3.0 mW/cm(2) 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.
The transmission and transport properties of non-conventional Fermi velocity graphene superlattices (FVGSLs) are studied. Arithmetic, regular and random distributions of the Fermi velocity barriers are assessed. A velocity position-dependent Dirac-like Hamiltonian is used to describe the charge carriers. The transfer matrix method and the Landauer-Büttiker formalism are implemented to obtain the transmission and the integrated transmission (conductance) at zero temperature. We find that arithmetic FVGSLs show peculiar transport characteristics as compared to regular and random FVGSLs. In particular, the arithmetic profile eliminates the regular and irregular oscillations of the integrated transmission typical of regular and random FVGSLs. More importantly, arithmetic FVGSLs keep the integrated transmission around the same value regardless of the size of the system, presenting even an increase (crossover) with the size of the system for large Fermi velocity ratios. This contrasts with the systematic reduction of the integrated transmission with the size of the system for regular and random FVGSLs. We delve into the possible causes of the crossover of the integrated transmission for arithmetic FVGSLs.
Molybdenum trioxide (MoO3) thin films with thicknesses 300, 400 and 500 nm were deposited on an FTO substrate by thermal evaporation method. The prepared thin films showed both thermochromic and photocatalytic dye degradation properties. The thermochromic property of the prepared thin films was induced by exposing the thin films to argon gas at a temperature varying from 100 degrees C to 300 degrees C (in steps of 50 degrees C). The photocatalytic dye degradation ability of the films were examined by the photodegradation of methylene blue (MB) dye solution under visible light irradiation. MoO3 thin film with 300 nm thickness is seen to have good thermochromic and photocatalytic dye degradation ability and both of these properties are necessary for smart window applications.
In this theoretical investigation, the binding energy, the binding energy Stark-shift, the dipole moment, the polarizability, and the diamagnetic susceptibility related with a confined shallow donor impurity in zinc blende GaN conical-shaped quantum dots are calculated under the effect of an electric field applied along the z-direction. Calculations have been made by using a variational approach within the infinite confining potential model and considering the parabolic conduction band and the effective mass approximations. The results suggest important dependencies of the calculated physical properties on the variation of the dot dimensions, axial impurity position, and the intensity of the applied electric field. It is observed that: i) the binding energy Stark shift increases up to a maximum value and then decreases with increasing the strength of the electric field, and it is strongly influenced by the impurity position and geometrical parameters, ii) for a fixed electric field value, the binding energy Stark shift is always an increasing function of the dot height, and iii) for fixed electric field values, the binding energy Stark shift shows a mixed behavior concerning the dot radius, i.e., for low field strength, the binding energy is always a growing function of the radius, and for large field strengths, such physical quantity grows with the radius up to a maximum and then decreases. Furthermore, the electric field (the strong quantum confinement) enhances slightly (diminishes) the diamagnetic susceptibility of impurity.
The work deals with the implementation of charge plasma concept towards the formation of graded doping profile in the Drain region of Tunnel FET (TFET) device architecture. This new and innovative concept of graded doping profile in the lateral direction holds its merit towards stopping the ambipolar conduction in TFETs without affecting its off and the on state performance. The proposed device i.e. Undoped Drain Graded Doping based TFET (UDGD TFET) architecture is highly effective in suppressing the gate to drain and therefore the total gate capacitance values and thus also seems promising towards reduction in the dynamic power dissipation in TFETs. The architecture has also shown significant improvements for RF application in terms of cut-off frequency, Gain Bandwidth and Transit Time with optimized parameters such as gate work function, drain workfunction, channel length and drain region length when compared to conventional Tunnel FETs.
As we all know, the normally-off HEMT is very important to the safety of power electronic systems. To increase the threshold voltage of the device, this article proposes to cover Al2O3 on the recessed P-GaN to form the recessed p-GaN HEMT covered with Al2O3. Through simulation calculation, covering Al2O3 on P-GaN can effectively increase the threshold voltage, but the saturation current and transconductance will be severely reduced. Therefore, this article optimizes the structure and proposes a composite recessed-gate HEMT for the first time. It can obtain high saturation current and high transconductance while maintaining a high threshold voltage. Compared with the recessed p-GaN HEMT covered with Al2O3, the transconductance and saturation current of the composite recessed-gate HEMT are increased by 13.14% and 121.33%, respectively, while the threshold voltage is only reduced by 4.44% (4.3 V). In addition, the gate dielectric has a greater impact on device performance. Therefore, this paper analyzes the influence of the thickness of the Al2O3 layer on the device through theoretical calculations and obtains the optimal value of the thickness. (T1 = 18.3 nm, Vth = 4.5 V, Isat = 456 mA/mm). The results show that the composite recessed gate has broad application prospects in the next generation of normally-off power device applications.
In this paper, a virtual GaAs1-xPx is used as a capping layer to InAs/GaAs quantum dot system. The strain profile, photoluminescence peak and rate of carrier escape out of the quantum dot inside the proposed structure are thoroughly investigated. The fractional composition of P in GaAs(1-x)P(x)is varied from 0.1 to 0.6 and a corresponding shifting of photoluminescence peak from 1176 nm to 1137 nm is observed. The thermal emission rate equal to 1.599 x 10(10) s(-1) and 6.437 1 x 10(8) s(-1) for electron and hole respectively are observed for the proposed structure. A two-dimensional strain matrix evaluated for the mentioned range of P composition exhibits smoother normalization of hydrostatic strain inside the capping layer as compared to GaAs0.86Sb0.14 capped device. Moreover, the effect of capping layer thickness on the strain profile, photoluminescence peak and carrier escape rate are investigated. The results of this analysis concludes that GaAs1-xPx for x = 0.1 is a useful candidate for the capping layer in quantum dot photodetector application.
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 substitutional 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.
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 perpendicular to 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.
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 ION, IOFF and ION/IOFF ratio. The scheme that yields the higher ION/IOFF ratio along with smaller IOFF, 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.
This work demonstrates a clear picture growth transition of aluminium nitride (AlN) films from the three-dimensional (3D) to the two-dimensional (2D) regime on the sapphire substrate at various temperatures using metal-organic chemical vapour deposition (MOCVD) under low reactor pressure. The high deposition rate of large 3D AlN islands that isolated each other change to 2D growth mode with a smoother surface as temperature increases from 800 ?C to 1340 ?C. From x-ray diffraction measurement, the AlN (100), AlN (002), and AlN (101) planes exhibit strong peak monocrystalline AlN (002) films as the temperature increase. It found that the AlN film grew at 1100 ?C in the Frank-van der Merwe or 2D growth mode exhibits the highest crystalline quality with the threading dislocation density around 2.21 x 10(9) cm(-2). In addition, the lattice vibrational parameters of the AlN films at 1100 ?C shows the lowest phonon damping from IR spectra results. Thus, this study details the AlN epitaxial films growth transition, which is crucial for growing high crystalline quality AlN layer using the MOCVD technique.
This numerical study deals with the CIGS solar cell considering Cd1-xZnxS buffer layer. The composition 'x' of the buffer layer is determined and its impact on the solar cell performance parameters is studied. The influence of the buffer layer thickness on quantum efficiency is also discussed. The tuned bandgap and optimized thickness of the Cd1-xZnxS buffer layer are then utilized to obtain the suitable bandgap of the CIGS absorber layer. The maximum power con-version zone is revealed in terms of the CIGS bandgap and the impact of this bandgap on spectral response as well as performance parameters are discussed. The Cd0.6Zn0.4S/CIGS interface is studied by varying the defect density from 10(10) cm(-3) to 10(16) cm(-3). The cell performances are also analyzed for the temperature ranging from 260 K to 350 K.
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 (IDS) 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 VGS 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, 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 erves 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.
The optical properties of interband and intersubband transitions in the GaNAsBi/GaAs quantum well (QW) heterostructure have been systematically studied by solving the Schro???dinger equation. Theoretical optimization of physical parameters of the GaNAsBi tensile strained layer has pointed out the importance of the polarization mode in the change of the optical absorption magnitude. Indeed, the N and Bi compositions and the quantum well width variations are thoroughly dis-cussed. For specific well parameters, the intersubband absorption spectrum of QW operating at 9:5 ??m as well as its magnitude dependence on the applied electric field and doping concentration are simulated. Based on the calculated absorption spectra, we can expect that the photodetection spectra of the future designed system can be tuned by controlling these relevant parameters.
Within the framework of the method of Lee-Low-Pines unitary transformations and variations, strong-coupling exciton-longitudinal-optical (LO) phonon interaction in asymmetric semi-exponential potential quantum wells was investigated. It is shown that the self-trapping energy, effective potential and vibration frequency of the exciton, depends significantly on the parameters of the confined potential, electron-hole distance and electron-hole mass.
We investigate theoretically, the GaAs/Al0.18Ga0.82As multi-quantum wells electronic band-structures and quantum magneto-transport properties at 1.6 K, using the envelope function with the effective mass formalism. The effect of well and barrier thicknesses on the band-structures and bandgap were studied. The bandgap decreases when the well thickness increases whereas an increase of barrier thickness leads to narrowing of sub-band width. The carrier's effective masses were calculated and the electronic transport dimensionality was determinates through the density of states. The inter-plateau widths of transitions in the quantum Hall effect increases with increasing inter-layer tunneling and well thickness disorder. Our results allowed easer interpretation of quantum Hall effect measurements in the literature and are necessary for the design and engineering of multiple quantum wells infrared detectors.
Designing broadband absorbers with only one metamaterial layer operating in the terahertz band is a relatively difficult challenge. In this paper, we proposed and investigate a broadband metamaterial perfect absorber (MPA) based on the graphene disk and square ribbon. The conductive substrate of this structure is made of gold and the middle dielectric layer of this structure is made of Rogers RT5880LZ, which acts as a spacer layer between the gold and graphene layers. This structure, while having only one metamaterial layer, also has the advantage of easy implementation because the graphene embedded on the dielectric surface does not have a complex design. The simulation results show that the proposed absorber can provide absorption above 90% with a bandwidth of 2.173 THz (1.482-3.655 THz). The fractional bandwidth ratio of the proposed structure is 85% for absorption greater than 90%. The absorption mechanism of this structure based on electric fields has been investigated. Since the design of the proposed broadband MPA is symmetrical, this structure is not sensitive to polarization and has a good bearing angle in the range of 0-30 degrees. The proposed structure is tunable because we can shift the absorption frequency by changing the Fermi level of graphene (mu(c)). The proposed absorber with these properties is suitable and flexible for applications such as sensing, imaging, and spectroscopy.
Correlation between electrical properties and growth dynamics for Si-doped AlGaN with Al mole fraction above 60% has been investigated. It is found that the electron concentration decreases significantly when decreasing the growth rate, while the electron mobility experiences a non-monotonic process of increasing at first and then decreasing. Combination of secondary ion mass spectroscopy and panchromatic cathodoluminescence results, reveals that the evolution of electrical properties mainly originates from compensation of III vacancy (V-III) to Si dopant, making V-III-nSi complexes, i.e., the concentrations of V-III-nSi complexes increase with decreasing the growth rate, implying high growth rate principle is vital for n-AlGaN.
This paper examines the variation of the linear, third-order nonlinear and total intersubband optical absorption (refractive index changes) coefficients of a donor impurity in multilayer cylindrical quantum dots (MCQDs), under the effect of temperature T and hydrostatic pressure P. Moreover, in this study, we also examined the effect of structure parameters on the optical absorption coefficients of the system. The Schrodinger equation describing the system is solved numerically by the finite element method (FEM) within the effective mass approximation. In our calculations, the confinement potential is modeled by a parabolic form in the radial direction and a square one in the z-direction. The optical absorption coefficients and refractive index changes have been investigated versus the quantum dot radius, indium composition and intensity of the incident electromagnetic for three allowed transitions: 1s - 1p, 2s - 1p and 1p - 1d. Our essential outcomes exhibit that the optical absorption coefficients and refractive index changes are strongly sensitive to the variation of quantum dot sizes, which enhance and blueshift as the quantum confinement is strong. On the contrary, the optical absorption coefficients and refractive index changes diminish and redshift as the quantum confinement reduces.
