Electron Tunneling Probability Research Articles

High-performance solar-blind photodetector of β-Ga2O3 grown on sapphire with embedding an ultra-thin AlN buffer layer

The authors reported the MOCVD growth of high-quality β-Ga2O3 on c-plane sapphire substrate, resulting in the achievement of high performance solar blind deep UV photodetectors by introducing an ultra-thin AlN buffer seed layer (BSL). Compared with the direct growth of Ga2O3 on the sapphire, the oxygen vacancy of β-Ga2O3 is reduced after introducing an AlN BSL and the full width at half maximum (FWHM) of (-201) diffraction peak becomes narrower. The dark current is reduced by 1000 times and from 10−10 A down to 10−13 A for the metal-semiconductor-metal planner photodetector of β-Ga2O3 thin film with the AlN BSL. And the detectivity reaches 4.65×1015 cm·Hz1/2·W at 5 V bias. This improvement in performance is derived from the improvement of the growth quality of β-Ga2O3 mediated by the AlN BSL due to the decrease of lattice mismatch. The defects in β-Ga2O3 are reduced, the carrier concentration is reduced, the Fermi level is shifted, the depletion region is widened, the probability of electron tunneling in the dark state is reduced, and the dark current is effectively reduced.

Giant tunneling resistance and robust switching behavior in ferroelectric tunnel junctions of WS2/Ga2O3 heterostructures: The influence of metal–semiconductor contacts

The ferroelectric tunneling junctions (FTJs) are widely recognized as one of the non-volatile memories with significant potential. Ferroelectricity usually fades away as materials are thinned down below a critical value, and this problem is particularly acute in the case of shrinking device sizes, thus attracting attention to two-dimensional ferroelectric materials (2DFEMs). In this work, we designed 2D ferroelectric Ga2O3-based FTJs with out-of-plane polarization, and the influence of metal–semiconductor contact in the electrode region on the system is considered. Here, using density functional theory combined with the non-equilibrium Green's function approach to quantum transport calculations, we demonstrate robust ferroelectric polarization-controlled switching behavior between metallic and semiconducting states in Ga2O3/WS2 ferroelectric heterostructures. The potential barrier of the metal–semiconductor contact in the electrode region is lower than that of the intrinsic material, thereby resulting in an increased probability of electron tunneling. Our results reveal the crucial role of 2DFEMs in the construction of FTJs and highlight the significant impact of electrode contact types on performance. This provides a promising approach for developing high-density ferroelectric memories based on 2D ferroelectric semiconductor heterostructures.

Out-of-Plane Electron Transport in Graphite Intercalation Compounds with Applications in Battery Anodes

Graphite intercalation compounds (GICs) are commonly used as anode materials for alkali metal-ion batteries, such as Li-ion and K-ion batteries. Although typically prepared as a low-stage intercalation compound (with a high concentration of the intercalating metal), over several electrochemical cycles, the distribution of intercalate within the graphite sample is expected to be non-uniform with domains of high-stage regions where the intercalant fraction is low [1]. The mechanism of interlayer electron transport in GICs strongly depends on the intercalation staging and temperature, and is expected to vary over the lifetime of a battery.High-stage GICs and highly oriented pyrolytic graphite (HOPG), which is the upper limit of infinite-stage GIC, have an out-of-plane electrical conductivity that exponentially increases with temperature, whereas low-stage GICs have a conductivity that decreases as a function of temperature [2, 3, 4]. Although out-of-plane electron transport in low-stage GICs can be described by a metallic conduction model, the mechanism of out-of-plane electron transport in HOPG and high-stage GICs is a hitherto unresolved problem [5]. Out-of-plane electrical conductivity for HOPG and high-stage GICs increases exponentially with temperature, which cannot be described by metallic conduction, nor by conventional impurity or defect hopping mechanisms [6].We propose a new mechanism of electron transport that takes place in HOPG and high-stage GICs at temperatures relevant to battery operation. Electrons are transferred between graphite and intercalant layers through tunneling that is enhanced by large amplitude out-of-plane phonon modes in graphite layers. Due to weak interlayer interactions in adjacent graphite layers, GICs can accommodate large amplitude phonon modes in the out-of-plane direction that locally enhance the interlayer electron tunneling probability. The tunneling enhancement is temperature dependent, and exponentially depends on the population of out-of-plane phonon modes excited at a given temperature. The expression for the conductivity 𝜎 for the phonon amplitude-driven tunneling mechanism as a function of temperature T is shown in Eq. 1; the exponential dependence of conductivity with temperature qualitatively agrees with experimental observations in HOPG and high-stage GICs. On a quantitative level, we also observe from Fig.1 that the theory agrees with experimental values for out-of-plane conductivity in HOPG.The phonon amplitude-driven tunneling mechanism of electron transport is relevant in describing the kinetic over-potential in batteries that employ layered materials as anodes in ambient temperature operating conditions, and optimally sizing the anode accounting for both electron transport and ion diffusion rates.

Quantum transport in WSe2/SnSe2 tunneling field effect transistors with high-k gate dielectrics

Combining two-dimensional materials and high-k gate dielectrics offers a promising way to enhance the device performance of tunneling field-effect transistor (TFET). In this work, the device performance of WSe2/SnSe2 TFET with various gate dielectric materials is investigated based on quantum transport simulation. Results show that TFETs with high-k gate dielectric materials exhibit improved on-off ratio and enhanced transconductance. The optimized WSe2/SnSe2 TFET with TiO2 gate dielectrics achieves an on-state current of 1560 μA/μm and a subthreshold swing (SS) of 48 mV/dec. The utilization of high-k gate dielectric materials results in shorter tunneling length, higher transmission efficiency, and increased electron tunneling probability. The performance of the WSe2/SnSe2 TFET would be affected by the presence of the underlap region. Moreover, WSe2/SnSe2 TFETs with La2O3 dielectric can be scaled down to 3 nm while meeting high-performance (HP) device requirements according to the International Technology Roadmap for Semiconductors (ITRS). This research presents a practical solution for designing advanced logic devices in the sub-5 nm technology node.

Thickness dependent field emission study of LaB6 coated Si nanowire arrays

A simple physical metal mask is efficiently employed to obtain an array of silicon (Si) nanowires (Si-NWs) on a Si substrate grown using the hot filament chemical vapor deposition route. Well adhered and uniform coating of different thicknesses (20 and 50 nm) of lanthanum hexaboride (LaB6) on Si-NWs was obtained using electron beam evaporation technique. The thickness of LaB6 coating was estimated from ellipsometry measurement. Structural, morphological, and chemical properties of the LaB6 coated Si-NWs (LaB6@Si-NWs) arrays were revealed using x-ray diffraction, field emission scanning electron microscope, transmission electron microscope, Raman spectroscopy, and x-ray photoelectron spectroscopy. Field electron emission characteristics of pristine Si-NW array and LaB6 coated Si-NWs array emitters were studied in planar diode configuration at a base pressure of 1 × 10−8 mbar. The values of turn-on field (current density ∼1 μA/cm2) were observed as ∼2.2, 1.2, and 1.6 V/μm for pristine Si-NWs, LaB6@Si-NWs_20, and LaB6@Si-NWs_50 array emitters, respectively. Furthermore, maximum emission current densities of ∼1276.81, 2763.64, and 2231.81 μA/cm2 have been extracted from the pristine Si-NWs, LaB6@Si-NWS_20, and LaB6@Si-NWS_50 array emitters at an applied field of 3.1, 2.7, and 2.7 V/μm, respectively. The LaB6@Si-NWS_20 array emitter demonstrated superior FEE properties as compared to the pristine Si-NWs and LaB6@Si-NWS_50 emitters. Furthermore, LaB6@Si-NWS_20 emitter depicted very good emission current stability tested at a preset value of 1 μA over a duration of 3 h. The enhanced FEE performance exhibited by the LaB6@Si-NWs_20 array emitter is attributed to reduction in effective work function and enhanced electron tunneling probability across the LaB6–Si interface.

Impact of capacitive effect on the J-V hysteresis in MgZnO/CdTe solar cells

In this study, we demonstrate that the current–voltage (J-V) hysteresis of MgZnO (MZO)/CdTe solar cells mainly originates from the modification of J-V curves by nonsteady-state photocurrent, which is correlative with low-frequency capacitance corresponding to the MZO/CdTe interface. The hysteresis was significantly strengthened by introducing oxygen into the CdTe growth atmosphere, and became more pronounced as the MZO thickness increased. The electrical properties of MZO in CdTe solar cells were analyzed in detail by using thermomechanical lift-off technique. The results showed that oxygen during CdTe growth seriously deteriorated the conductivity of MZO by reducing the concentration of oxygen vacancy. Furthermore, a spike-like conduction band offset (CBO) greater than 0.25 eV was determined at MZO/CdTe interface due to the formation of Mg-rich surface layer. Thus, the low-frequency capacitance originating from electron accumulation at MZO/CdTe interface was increased due to the less probability of electron tunneling through the interface barrier. SCAPS simulations confirmed that the low-frequency capacitance was caused by substantially reduced conductivity of MZO and large CBO at MZO/CdTe interface. The experimental and simulation results indicate that the J-V hysteresis of MZO/CdTe cells can be suppressed by reducing low-frequency capacitance, which is achievable through enhanced electron transport at MZO/CdTe interface.

A Study on the Increase of Leakage Current in AlGaN Detectors with Increasing Al Composition.

The dark leakage current of AlxGa1-xN Schottky barrier detectors with different Al contents is investigated. It was found that the dark leakage of AlxGa1-xN detectors increased with increasing Al content. The XRD and SIMS results showed that there was no significant difference of the dislocation density and carbon impurity concentration in five AlxGa1-xN samples with different Al content. This was likely not the main reason for the difference in dark leakage current of AlxGa1-xN detectors. However, the results of positron annihilation showed that the vacancy defect concentration increased with increasing Al content. This was consistent with the result that the dark leakage current increased with increasing Al content. With the increase of vacancy concentration, the vacancy defect energy levels also increased, and the probability of electron tunneling through defect levels increased. In contrast, the Schottky barrier height decreased, which eventually led to the increase of dark leakage current. This discovery should be beneficial to an accurate control of the performance of AlxGa1-xN detectors.

Interfacial contact barrier and charge carrier transport of MoS2/metal(001) heterostructures.

The rapid rise of two-dimensional (2D) materials has aroused increasing interest in the fields of microelectronics and optoelectronics; various types of 2D van der Waals heterostructures (vdWHs), especially those based on MoS2, have been widely investigated in theory and experiment. However, the interfacial properties of MoS2 and the uncommon crystal surface of traditional three-dimensional (3D) metals are yet to be explored. In this paper, we studied heterostructures composed of MoS2 and metal(001) slabs, based on the first-principles calculations, and we uncovered that MoS2/Au(001) and MoS2/Ag(001) vdWHs reveal Schottky contacts, and MoS2/Cu(001) belongs to Ohmic contact and possesses ultrahigh electron tunneling probability at the equilibrium distance. Thus, the MoS2/Cu(001) heterostructure exhibits the best contact performance. Further investigations demonstrate that external longitudinal strain can modulate interfacial contact to engineer the Schottky-Ohmic contact transition and regulate interfacial charge transport. We believe that it is a general strategy to exploit longitudinal strain to improve interfacial contact performance to design and fabricate a multifunctional MoS2-based electronic device.

Anomalous Klein tunneling in two-dimensional black phosphorus heterojunctions.

We investigate the role of heterojunctions of few-layer black phosphorus (BP) with band gap inversion in governing the quantum transport behaviors. Numerical results show that in the armchair junction, electron tunneling probability occurs under approximately normal incidence with its magnitude T > 0.5. More interestingly, when different band gaps are taken into account on two sides of this junction, the maximum transmission appears away from the center of the valley, leading to the occurrence of anomalous Klein tunneling. Such a result tends to be independent of the width and height of the potential barrier. On the other hand, in the zigzag junction, electron transmission arises in a larger range of angles, and perfect electron transmission (T = 1.0) or reflection appears under specific band gap configurations. These findings provide a new understanding for the study of Klein tunneling and anomalous Klein tunneling based on tunable band gap BP or other two-dimensional Dirac semimetals.

Theory of Protein Charge Transfer: Electron Transfer between Tryptophan Residue and Active Site of Azurin.

One reaction step in the conductivity relay of azurin, electron transfer between the Cu-based active site and the tryptophan residue, is studied theoretically and by classical molecular dynamics simulations. Oxidation of tryptophan results in electrowetting of this residue. This structural change makes the free energy surfaces of electron transfer nonparabolic as described by the Q-model of electron transfer. We analyze the medium dynamical effect on protein electron transfer produced by coupled Stokes-shift dynamics and the dynamics of the donor-acceptor distance modulating electron tunneling. The equilibrium donor-acceptor distance falls in the plateau region of the rate constant, where it is determined by the protein-water dynamics, and the probability of electron tunneling does not affect the rate. The crossover distance found here puts most intraprotein electron-transfer reactions under the umbrella of dynamical control. The crossover between the medium-controlled and tunneling-controlled kinetics is combined with the effect of the protein-water medium on the activation barrier to formulate principles of tunability of protein-based charge-transfer chains. The main principle in optimizing the activation barrier is the departure from the Gaussian-Gibbsian statistics of fluctuations promoting activated transitions. This is achieved either by incomplete (nonergodic) sampling, breaking the link between the Stokes-shift and variance reorganization energies, or through wetting-induced structural changes of the enzyme's active site.

Fine modulation of the energy band strategy to control the carrier confinement capability of digital alloys

In this paper, a strategy to finely modulate the energy band structure to control the carrier confinement capability of digital alloys (DA) is proposed. Strain analysis shows that As and Sb atoms are exchanged within the AlAsSb DA. The bottom of the corrected potential well is low on the left and high on the right in the growth direction, resulting in a higher band offset of the AlSb potential barrier layer on the left side of the potential well than on the right side. The modulation of the band leads to a higher probability of electron tunneling in DA under the action of an electric field opposite to the growth direction. Conversely, it is difficult for the electrons to tunnel into the lower energy level potential wells. The I–V curve of DA shows that the current value under positive bias is significantly smaller than the value under negative bias when the voltage is higher. The measured results correspond perfectly with the modified energy band model, which verifies the feasibility of energy band modulation. This is important for the structural design of DA and the reduction of dark current in optoelectronic devices.

A z-axis tunneling microscope for undergraduate labs

We present the design and construction of a laboratory apparatus that provides advanced undergraduates with hands-on observations of electron quantum tunneling and the electronic density of states of various materials. The instrument is inspired by the scanning tunneling microscope (STM), but its implementation is simplified by limiting the tip motion to the single dimension along the tip-sample separation (z-axis); we refer to the device as the z-axis tunneling microscope (ZTM). Students are able to use the ZTM to measure electron tunneling probability as a function of barrier width, estimate relative material work functions, and observe differences in local electronic structure among metals, semimetals, and semiconductors. We share results obtained by third-year undergraduate physics students using the instrument for their final projects in an advanced instructional lab course.

(Invited) Development of THz-Field-Driven Scanning Tunneling Luminescence Spectroscopy for Future Investigation of Exciton Dynamics

Exciton dynamics is responsible for the photophysical and photochemical functions, such as energy harvesting, light emission, and photosynthesis. In particular, energy conversions, transfers, and dissipations at interfaces and nanostructures govern the dynamics of excitons. Nevertheless, the spatial resolutions of conventional optical methods are limited to several hundred nanometers due to the diffraction limit of light. Luminescence measurements combined with scanning tunneling microscopy (STM) enable to investigate optical properties with sub-nanometer spatial resolution in various systems such as metals[1], semiconductors[2], 2D materials[3], and molecules[4-5]. In this method, the scanning tunneling luminescence (STL) spectroscopy, photons induced by the tunneling current of STM are detected. Since the tunneling current can be controlled with atomic spatial resolution, it is possible to investigate optical phenomena in localized regions. While STL spectroscopy is a powerful tool for investigating exciton dynamics with atomic-scale spatial resolution, the time resolution of STL spectroscopy is limited because it uses “steady-state” tunneling current for the excitation. Therefore, this method cannot be applicable to track the ultrafast exciton dynamics in real-time.For overcoming the limitation of time resolution of STM, a single-cycle terahertz (THz) electric field has recently been installed to drive tunneling electrons[6-9]. By coupling the THz pulse to an atomically sharp metal tip of STM, the electric field is confined to the tip, and it enables to manipulate the tunneling electrons with extremely high spatiotemporal resolution. This method, THz-STM, has been utilized to track the ultrafast carrier dynamics[6-8] and motion of a molecule[9] with sub-picosecond time resolution. In this work, we combined a photon detection system with THz-STM to establish THz-STL spectroscopy (Fig. 1a). We measured visible photon emission from the radiative decay of a localized plasmon as the first demonstration of THz-STL spectroscopy[10]. We anticipate that the THz-STL spectroscopy will open new avenues for “real-time” and “real-space” investigations of exciton dynamics in near future.In this work, we generated single-cycle THz pulses via optical rectification of laser pulses from a Yb fiber laser in a LiNbO3 prism using a tilted-pulse-front configuration (Fig. 1b). The generated THz pulses were guided into a low-temperature STM and focused to the STM junction (Fig. 1a). Figure 1c shows a current trace on Ag(111) surface, where the current induced by the THz pulses was measured as 2.65 pA. Based on the simulation of electron tunneling probability, the maximum magnitude of the voltage applied by the THz pulse was estimated to be ~6.5 V. Figure 1d shows STL spectra when the THz pulse was either introduced to the STM (red) or blocked (grey). Whereas no peak is seen in the grey spectrum, a broad peak ranging from 1.3 eV to 2.3 eV appears in the red spectrum, which is originated from the radiative decay of a plasmon localized in the gap.In this presentation, we would like to discuss the detailed mechanism of plasmon excitation by THz-field-driven electrons as well as the challenges of applying THz-STL to the real-time investigation of exciton dynamics in a molecule.[1] R. Berndt et al., Phys. Rev. Lett. 67, 3796 (1991). [2] J. K. Gimzewski et al., Z. Phys. B Condensed Matter 72, 497 (1988). [3] Schuler et al., Sci. Adv. 6, eabb5988 (2020). [4] H. Imada et al., Nature 538, 364 (2016). [5] K. Kimura et al., Nature 570, 210 (2019). [6] T. L. Cocker et al., Nat. Photon. 7, 620 (2013). [7] K. Yoshioka et al., Nat. Photon. 10, 762 (2016). [8] V. Jelic et al., Nature Physics 13, 591 (2017). [9] D. Peller et al., Nature 585, 58 (2020). [10] K. Kimura et al., ACS photon. 8, 982 (2021). Figure 1

Regulating the π-π interaction with shortened electron tunneling distance for efficient charge storage

Coupling organic redox moieties with carbon through π–π interaction is a widely used strategy to boost the energy densities of electrochemical capacitors, but the low electron tunneling probability of π–π interaction through the out-of-plane direction intrinsically limits the charge storage capacity and rate capability. Here we rationally construct B involved functional sites on the surface of porous carbon fibers for coupling hydroquinone (HQ) molecules with enhanced π–π interaction, which enables exceptional charge storage performance by regulating the interfacial charge tunneling behavior. The designed HQ-carbon composites deliver an attractive areal capacitance of 2.68 F cm−2 at 2 mA cm−2 and retain 2.10 F cm−2 at 40 mA cm−2, representing the highest areal capacitance among the ever-reported organic redox moiety/carbon systems. Meanwhile, maximum volume energy density and power density of 12.2 mWh cm−3 and 3683 mW cm−3 are demonstrated by assembling an asymmetric supercapacitor with Ti3C2Tx. The theoretical calculation indicates the decreased tunneling distance originating from the regulated π–π interaction contributes to the fast kinetics of proton-involved charge-storage process. The capability of regulating the charge transfer behavior offers a new vision to couple organic redox moieties with carbon for energy storage and beyond.

Comparing the nature of quantum plasmonic excitations for closely spaced silver and gold dimers.

In the new field of quantum plasmonics, plasmonic excitations of silver and gold nanoparticles are utilized to manipulate and control light-matter interactions at the nanoscale. While quantum plasmons can be described with atomistic detail using Time-Dependent Density Functional Theory (DFT), such studies are computationally challenging due to the size of the nanoparticles. An efficient alternative is to employ DFT without approximations only for the relatively fast ground state calculations and use tight-binding approximations in the demanding linear response calculations. In this work, we use this approach to investigate the nature of plasmonic excitations under the variation of the separation distance between two nanoparticles. We thereby provide complementary characterizations of these excitations in terms of Kohn-Sham single-orbital transitions, intrinsic localized molecular fragment orbitals, scaling of the electron-electron interactions, and probability of electron tunneling between monomers.

Quasi-Compact Model of Direct Source-to-Drain Tunneling Current in Ultrashort-Channel Nanosheet MOSFETs by Wavelet Transform

We present an analytical approach for the calculation of direct source-to-drain tunneling (DSDT) probability of electrons in gate-all-around (GAA) silicon nanosheet (SiNS) MOSFETs. The used method is based on the wavelet transform and leads to a quasi-compact model (QCM) for the DSDT current of ultrashort-channel devices. Among them, we introduce a four-piece parabolic approximation method for the conduction band edge and present analytical expressions for the tunneling distances of electrons with different energy levels. The development of a QCM is achieved by limiting the number of interpolation points for the tunneling current density to seven specific electron energies, distributed around the energy level that makes the largest contribution to the tunneling current. A further simplification is achieved by the Gaussian approximation of the tunneling current density in transverse direction so that only the center and surface potentials ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Phi _ {\text {C}}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Phi _ {\text {S}}$ </tex-math></inline-formula> ) at the barrier are of interest for the modeling. For comparison, all those approximations are also implemented in the Wentzel–Kramer–Brillouin (WKB) approximation. Furthermore, the approach is verified by nonequilibrium Green’s function (NEGF) simulation.

Transition from Schottky-to-Ohmic contacts in 1T VSe2-based van der Waals heterojunctions: Stacking and strain effects

For its ultra-high conductivity, room temperature ferromagnetic, and robust stability, monolayer 1T VSe2 acts as a promising two-dimensional (2D) material for new spintronics device. However, Ohmic contact with semiconductor is a desirable property for high-performance devices due to the obstruction of strong Fermi level pinning effect at the Schottky interface. Herein, we employ density functional theory to explore a series of VSe2-based van der Waals heterojunctions, in which Ohmic contact is only found in the VSe2-multilayer MoSSe junctions due to the destruction of depletion region and the increase of electron tunneling probability. Moreover, applying appropriate biaxial tensile stress can also lead to the transition from Schottky-to-Ohmic contact in the VSe2-based metal-semiconductor junctions. Our results provide an avenue for the design of future 2D VSe2-based electronics.

Photo- and electroluminescence features of films and field effect transistors based on inorganic perovskite nanocrystals embedded in a polymer matrix

The optical and electrical properties of films and field-effect transistors (FETs) based on pure MEH-PPV, neat CsPbBr3 nanocrystals (NCs), and MEH-PPV:CsPbBr3 NCs composites with different contents of CsPbBr3 NCs are investigated. The films were characterized by absorbance, atomic-force microscope and current-voltage characteristics (I-Vs) techniques. Relative PL and EL intensities and PL spectra of the pure MEH-PPV, neat CsPbBr3 NCs and MEH-PPV:CsPbBr3 NCs films were measured at 300 K at various levels of optical and electrical excitation power; these dependencies of the PL and EL intensities turned out to be sublinear and superlinear respectively. FETs based on MEH-PPV:CsPbBr3 NCs (1:1) films exhibit I-Vs at 290 – 100 K a dominant hole transport mechanism. The mobility of charge carriers was determined at 290 K for neat CsPbBr3 NCs (for electrons: 2.7 10−2 cm2/Vs) and MEH-PPV:CsPbBr3 NCs (1:1) (for holes: 9 cm2/Vs). The temperature dependence of the hole mobility μFET(T) of FETs based on MEH-PPV:CsPbBr3 NCs (1:1) films characteristic of the hopping mode. It was found that the superlinearity of the dependence of EL of MEH-PPV:CsPbBr3 NCs LE-FETs at 290 K increases with increasing concentration of CsPbBr3 NCs due to efficient energy transfer between CsPbBr3 NCs and the MEH-PPV polymer matrix, and also because of the probability of electron tunneling through the potential barrier to electrode. It is expected that the obtained MEH-PPV:CsPbBr3 NCs nanocomposite films will be useful for efficient applications in nanotechnology LEDs, FETs and LE-FETs.

Current Analysis of Single Electron Transistor Based on Graphene Double Quantum Dots

The single electron transistors (SETs) as low power devices are suitable candidates for nanoscale circuit in future technology. These nanoelectronic devices operate based on an electron tunneling. However, coulomb blockade effect prevents single electron transfer between island and coulomb barriers in some conditions. This phenomenon causes zero-conductance region in low bias that is operation limitation of SET. This problem can be solved by using multiple islands in SET structure which their materials are two dimensional carbon based materials such as graphene. Increasing the number of islands effects on probability of electron tunneling. This factor not only rises speed of electron transfer but also it can reduce gap conductance in SET. In this research, current of graphene double quantum dots SET is analyzed and modeled. Moreover effects of graphene length, applied gate voltage and temperature on current SET are investigated. Furthermore effect of number of islands on SET current is evaluated with comparison their charge stability diagrams which are results of SET simulation by software.

Effect of Barrier Thickness and Height on the Transmission Coefficient of GaAs/Ga1–xAlxAs Quantum Cascaded Laser (QCL)

This paper demonstrates the impact of barrier thickness on the transmission coefficient of GaAs/Ga1–xAlxAs quantum cascaded laser (QCL). The transmission coefficient is the important measurable quantity to predict the properties of quantum cascaded laser (QCL). This paper also includes the effects of the change in composition 'x' of the barrier height on transmission coefficient. In this study, GaAs/Ga1–xAlxAs QCL structures have been selected with operating temperature at T = 10 K. The calculated results show that at lower temperature when the thickness of barrier is less, the probability of electron tunneling is high, therefore, transmission coefficient is high. When we increase the barrier height it results in lowering the probability of electron tunneling, hence transmission coefficient is decreases. The calculated results justified the reported results of other workers.