Two-dimensional Potential Profile Research Articles

Analytical Model of Conventional and Rectangular Core-Shell-based Double Gate Junctionless MOS

In this paper, an analytical, detailed two-dimensional potential profile model of a newly proposed rectangular core-shell-based double-gate junctionless metal oxide semiconductor (RCS-DGJLMOS) is presented. A detailed numerical solution of the model is presented for conventional n-type double-gate junctionless MOS (DGJLMOS), and the changes made in the model for RCS-DGJLMOS are extensively presented. While solving 2-D Poisson equations, a parabolic potential is assumed along the silicon thickness for both devices. The characteristics of the potential profile are studied on varying doping concentrations, dielectric constants, silicon thickness, and gate oxide thickness in conventional DGJLMOS, whereas the thickness of the core, total silicon thickness, dielectric constants, and core doping are varied in RCS-DGJLMOS. The detailed study on potential profile reveals the huge depletion of RCS-DGJLMOS as compared to conventional DGJLMOS due to the presence of oppositely doped core and, therefore, improves the device performance. Furthermore, the transfer characteristics are also presented for both devices. The analytical results for DGJLMOS and RCS-DGJLMOS have been assessed with Technology Computer Aided Design (TCAD) software. The analytical results obtained from the proposed model are verified with the simulation data.

Characterization of acceleration zone shifting in an anode-layer-type Hall thruster RAIJIN66

The location of the ion acceleration zone has been known to affect the performance and lifetime of a Hall thruster. Herein, the magnetic field in the anode-layer-type Hall thruster RAIJIN66 was designed to shift the acceleration zone downstream beyond the discharge channel exit. To examine the effectiveness of the design concept, plasma diagnosis using an emissive probe was conducted to obtain a one-dimensional plasma profile on the channel centerline. In addition, a two-dimensional potential profile was obtained to observe the effects of the presheath on the shifted potential structure. The results proved that the acceleration zone was pushed downstream along with the shifted magnetic field. With increasing discharge voltage, the axial length of the acceleration zone contracted at around the peak of the radial magnetic flux density. The ion current density lost to the guard-ring was estimated to be 9.9 mA/cm2, which is comparable to the current density from the magnetically shielded stationary plasma thrusters. Furthermore, the measured two-dimensional potential distribution revealed the existence of a structure that attracted ions to the wall.

Barrier model in muon implantation and application to Lu2O3

In implantation experiments, the implanted particle is shot with a certain energy into the material and comes to rest at a site which may not correspond to the final position. The rearrangements of the surrounding atoms to accommodate the particle, i.e., the reaction with the host atoms may require some time and lead to delayed formation of the final states. In the case of the implantation of positive muons, this rearrangement process can be followed on a timescale of nanoseconds to microseconds. A delay is expected if an energy barrier inhibits the prompt reaction. We note that the barrier height may change during the rearrangement of the lattice, thus giving rise to a two-dimensional potential profile for the conversion process. The barrier model describes the reaction path of the muon in analogy to the passage over a mountain with a saddle point. The passing over the saddle point corresponds to the lowest energy trajectory. As an example, we discuss the application of the barrier model to solid ${\mathrm{Lu}}_{2}{\mathrm{O}}_{3}$.

2D potential measurements by applying automatic beam adjustment system to heavy ion beam probe diagnostic on the Large Helical Device.

Two-dimensional potential profiles in the Large Helical Device (LHD) were measured with heavy ion beam probe (HIBP). To measure the two-dimensional profile, the probe beam energy has to be changed. However, this task is not easy, because the beam transport line of LHD-HIBP system is very long (∼20 m), and the required beam adjustment consumes much time. To reduce the probe beam energy adjustment time, an automatic beam adjustment system has been developed. Using this system, required time to change the probe beam energy is dramatically reduced, such that two-dimensional potential profiles were able to be successfully measured with HIBP by changing the probe beam energy shot to shot.

Two-dimensional potential profile and density measurements by use of an improved gold neutral beam probe

An improved gold neutral beam probe system has been developed in order to measure both the potential profile and the electron density profile simultaneously at the central cell of the tandem mirror GAMMA10. A gold film detector was also developed in order to measure the plasma density profile. The yield curves of secondary electrons were measured as a function of the incident angle and electron energy using both the gold neutral beam and ultraviolet ray injection. Time evolution of the plasma line density was measured by adjusting the incident angle and adding a beam chopping method. The result is in good agreement in comparison with the line density measured using a microwave interferometer. It was found that this film detector is very useful for simultaneous measurements of the electrostatic potential and plasma density.

Simulations of the electrostatic potential in a thin silicon specimen containing a p-n junction

ABSTRACTThe measurement of potentials associated with dopant atoms in semiconductors at nanometer spatial resolution using off-axis electron holography is known to be affected by the presence of the surfaces of thin specimens. In particular, the potential across a p-n junction is often found to be lower than would be expected from predicted properties of bulk devices. Here we present simulations of two-dimensional potential profiles within a thin (<1 µm) parallel-sided specimen containing a p-n junction. We find that the potential across the p-n junction is always smaller, when projected through the specimen, than would be expected from the properties of the bulk material. Crucially, the step in potential across the junction is independent of the value of the potential on the surface of the specimen for high dopant concentrations (>1017 cm−3). The simulations are compared with experimental data. Although they can account for some of the reduction in the observed potential, they do not fully explain the experimental results.

Bipolar conduction and drain-induced barrier thinning in carbon nanotube FETs

The drain current-voltage (I-V) characteristics of Schottky-barrier carbon nanotube field-effect transistors (FETs) are computed via a self-consistent solution to the two-dimensional potential profile, the electron and hole charges in the nanotube, and the electron and hole currents. These out-of-equilibrium results are obtained by allowing splitting of both the electron and hole quasi-Fermi levels to occur at the source and drain contacts to the tube, respectively. The interesting phenomena of bipolar conduction in a FET, and of drain-induced barrier thinning (DIBT) are observed. These phenomena are shown to add a breakdown-like feature to the drain I-V characteristic. It is also shown that a more traditional, saturating-type characteristic can be obtained by workfunction engineering of the source and drain contacts.

Two-dimensional nonlocal model of axially and radially inhomogeneous plasma of cylindrical magnetron discharge.

A cylindrical magnetron discharge (CMD) with two coaxial electrodes, a uniform axially directed magnetic field, and discharge ends closed by the shields biased at the cathode potential is considered. The presence of the shields creates axial inhomogeneity of plasma, which is taken into account in this study. At low pressures and small magnetic fields the pronounced nonlocal regime of the electron distribution function (EDF) formation is realized. The electron component is analyzed on the basis of radially and axially inhomogeneous Boltzmann kinetic equation. Unmagnetized electrons that move in axial direction are trapped in the axial potential well, their energy relaxation length exceeds the discharge vessel length, and the kinetic equation can be averaged over axial flights of electrons. Using a model two-dimensional potential profile, the EDFs at the different axial positions are obtained and two-dimensional distributions of the electron density, ionization rate, and current on cathode are calculated. The results of the modeling and experiments are compared for the dc CMD in Ar at a pressure of 3 Pa, magnetic field strength of 10 mT, and current of 150 mA.

Analysis of leakage current in GaAs/AlGaAs buried-heterostructure lasers with a semi-insulating GaInP:Fe burying layer

The leakage current in recently demonstrated GaAs/AlGaAs buried heterostructure (BH) lasers with a semi-insulating (SI) GaInP:Fe burying layer has been theoretically and experimentally analyzed. Calculated current–voltage characteristics of n-GaAs/SI-GaInP/n-GaAs and p-GaAs/SI-GaInP/p-GaAs planar configurations have been studied specially to assess the behavior of SI-GaInP:Fe under electron and hole injection. Two-dimensional potential profiles have been used to explain the leakage current mechanism in the SI-GaInP-buried lasers. Simulations reveal that the total leakage current decreases as the active trap concentration in the SI-GaInP:Fe burying layer is increased as expected, but the leakage current is strongly confined in the vicinity of the active region where the local leakage current density increases significantly as the trap density increases. It is found that the insertion of a n-GaInP hole blocking layer between the p-metal and the SI-GaInP layer decreases the total leakage current. Experimental light–current and current–voltage characteristics of fabricated lasers with and without an additional n-GaInP layer, and electroluminescence (EL) emitted from the burying GaInP:Fe layers corroborate qualitatively the simulations and demonstrate the benefits of using a n-GaInP layer for reducing leakage current in these type of lasers.

Near-Field Optical Imaging and Spectroscopy of Single GaAs Quantum Wires

Low-dimensional semiconductor structures grown by molecular beam epitaxy on a patterned (311)A GaAs substrate are investigated by near-field spectroscopy at a temperature of 10 K. In particular, the two-dimensional potential profiles of quantum wire and coupled wire-dot structures are determined from photoluminescence (PL) measurements with a spatial resolution of 150 nm. Also presented is an optical method for investigating carrier transport in low-dimensional systems involving performing spatially resolved PL excitation measurements on the wire-dot structure.

Fast two-dimensional potential measurement at the thermal barrier region of the tandem mirror Gamma 10

A gold neutral beam probe system was improved by adopting a multichannel ion detector and adding sweeping functions of beam energy, deflector voltage, and electrode voltage of the analyzer to the system to measure the fluctuations and time evolution of the two-dimensional space potentials with fast resolving time during one shot. Positions of the beam spot on the multichannel detector corresponding to the ionizing points of the beam in the plasma were simulated precisely as a function of the beam energy and the injection angle. A potential derivation formula was determined taking into consideration both the numerical and experimental results, and the reproducibility of the potential profile was checked. Two-dimensional potential profiles were measured in the optimization experiment of the microwave injection angles for formation of the plug potential.

Potential Profile Measurement of GaAs HEMTs and Heterostructures Using Kelvin Probe Force Microscopy.

Kelvin probe force microscopy (KFM) was successfully applied to the two-dimensional potential profile measurements of the cleaved surface of GaAs HEMTs under bias voltage. A high-field region was observed at the drain-side edge of the gate. By measuring the cleaved surfaces of GaAs/AIAs and InAlAs/InGaAs heterostructures, we have obtained potential profile reflecting the work function difference of the material. The minimum distinguishable thickness of the InAlAs/InGaAs heterostructure by the KFM was 40nm. The present KFM technique combined with device simulation will provide a powerful tool for analyzing the electrical properties of the device, not only GaAs devices but also others.

Two-dimensional potential profile measurement of GaAs HEMT's by Kelvin probe force microscopy

Two-dimensional (2-D) potential profile of GaAs HEMT's under bias voltage has been successfully measured by combining Kelvin probe force microscopy with cleavage of the HEMT's. The spatial resolution evaluated by measuring GaAs-AlAs multiquantum-well structure was less than 70 nm. The measured depth profile of the potential shows a potential knee, which probably originates from the charge trapped at the interface between the epitaxial layer and the substrate. The high-field region is observed at the drain-side edge of the gate. The present KFM technique will yield a powerful tool for analysis of the electrical properties of the devices.

Enhancement of the thermal barrier depth and two-dimensional potential profiles in GAMMA 10

Gold neutral beam probes are used for the determination of the space potentials at the thermal barrier cells and the central cell of the GAMMA 10 tandem mirror. The thermal barrier potential is determined by simultaneous measurements of the on-axis space potentials at both locations. Equipotential contours over a cross-section at the barrier are measured by sweeping the probing beams with different beam energies. The enhancement of the thermal barrier depth and of the neoclassical radial ion transport in relation with two-dimensional space potential profiles has been studied in GAMMA 10 for the case of low density experiments.

A new method based on the superposition principle for the calculation of the two-dimensional potential in a buried-channel charge-coupled device

An analytical method for computing the two-dimensional potential profile in buried-channel charge-coupled devices with zero gate separation is presented. The method invokes the superposition principle in all three major regions of the device, namely: oxide, buried n-layer, and p-type substrate. This leads to a solution for the potential distribution in these regions which satisfies all boundary conditions. One of the superposed potentials appears in the homogeneous form of Poisson's equation and it is demonstrated here that for the device structure under consideration, a simple method of solving for this potential results from the use of conformal mapping.