Papers by Keyword: Tunneling Current

Abstract: In this paper, an analytical model for evaluation of tunneling current density of ultra-thin Metal Oxide Semiconductor (MOS) devices is presented. Results have been obtained for a wide variation of oxide thickness and biasing condition having doping concentration of 1 x 10¹⁷ cm^-3. The investigation for the tunneling current density is limited to low temperatures, so that any thermal involvement to current flow can be neglected. The self-consistent oxide tunneling model has been used for device simulation, which is simple to implement and assist in the study of deep sub-micron MOS gate current effects, therefore correctly calculate the terminal current. Tunnel resistivity is also evaluated utilizing this tunneling current density model. Theoretical predictions are compared with the results obtained by the 2-D numerical device simulator ATLAS, good agreements between the two are observed.

Abstract: We have developed a model of the tunneling current in n-p-n bipolar transistor based on armchair graphene nanoribbon (AGNR). Airy-wavefunction approach is employed to obtain electron transmittance, and the obtained transmittance is then used to obtain the tunneling current. The tunneling current is calculated for various variables such as base-emitter voltage, base-current voltage, and AGNR width. It is found that the tunneling current increases with increasing the base-emitter voltage or the base-collector voltage. This result is due to the lowered barrier height of the base region caused by the increase in the base-emitter voltage or the base-collector voltage. In addition, the tunneling current density increases with the width for narrow AGNR and, on the other hand, it decreases for wide AGNR. This finding might be due to the contributions of the band gap energy and the electron effective mass of AGNR which are inversely proportional to the AGNR width.

Abstract: The verification of calculation results of the isotropic and anisotropic-isotropic mass models in Al/SiO₂/Si MOS capacitor against the experimental data is presented, using electron transversal velocity as a fitting parameter. In the accumulation condition, the comparison yields the electron velocity of 2.8 x 10⁶ m/s for both isotropic and isotropic-anisotropic mass models. The tunneling current values for both models are slighly different with experimental data. In the inversion condition, the values of electron velocity for isotropic and isotropic-anisotropic model are 1.55 x 10⁶ m/s and 1 x 10⁵ m/s, respectively. The calculation results of isotropic-anisotropic mass model appear to be closer to the experimental data compared to those of isotropic mass model, due to the effect of electron effective mass.

Abstract: Tunneling current in an armchair graphene nanoribbon (AGNR) tunnel field-effect transistor (TFET) was modeled. A linear equation was employed in describing a potential distribution within the AGNR due to its simplicity. A parabolic dispersion and an electron effective mass obtained by approximating k_x 0 to the parabolic dispersion were applied to AGNR. In order to obtain electron transmittance, electron wavefunctions in AGNR were based on Airy functions. The obtained transmittance was then applied to calculate the tunneling current by employing the Landauer formula. The calculated results showed that the tunneling current increases with the AGNR width. It was also shown that the tunneling current increases as temperature decreases. In addition, the gate voltage influences the saturation condition of tunneling current in AGNR TFETs.

Abstract: Electron tunneling current in an isotropic metal-oxide-semiconductor (MOS) capacitor with a high-κ dielectric stack has been studied by considering the effect of charge trapping. The transmittance was analytically calculated by employing an Airy-wavefunction approach and including a coupling term between the transverse and longitudinal kinetic energies which is represented by an electron phase velocity in the gate. The transmittance was then applied to obtain tunneling currents in isotropic n⁺poly-Si/HfSiO_xN/trap/SiO₂/Si (100) MOS capacitors for different electron gate phase velocities and trap depths and widths. The calculated results show that the transmittance and tunneling current increase as the electron gate velocity decreases. In addition, the increase in the trap depth and width enhances the tunneling current.

Abstract: In this paper, we have computed electron tunneling currents in TiN_x/HfSiO_xN/SiO₂/Si (100) MOS capacitors by including a coupling term between transverse and longitudinal kinetic energies which is represented by an electron phase velocity in the gate. The effective mass of the substrate is considered as an isotropic mass. The transmittance was analytically calculated by employing an Airy-wavefunction approach, and the obtained transmittance was then utilized to calculate the tunneling current for different nitrogen compositions in the TiN_x metal gate and the equivalent oxide thicknesses (EOTs) of HfSiO_xN. It was shown that the tunneling current reduces considerably as the nitrogen composition of the TiN_x metal gate decreases. It was also shown that the increase in the EOT reduces the tunneling current. In addition, the tunneling current shows an oscillatory behavior at high oxide voltages.

Abstract: Scanning tunneling microscopy is one of the surface measurement instruments in nanotechnology field, and the vertical resolution is about 0.01nm. So it is easily affected by the external micro vibration, conversely, we can measure the micro vibration using the working principle of STM. As we all know, the tunneling effect is the negative index relation between the tunneling current and the tunneling gap. On the other hand, the vibration measurement results can be used to offer the foundation in order to reduce the influence of micro random vibration for STM, it is necessary to measure the external vibration to compensate the experiment results of scanning tunneling microscoy. So the experimental device is developed and experiment of vibration detection is made. The experiment results show that results have high sensitivity, good frequency characteristic and the same vibratory response characteristic consistent with scanning tunneling microscopy.

Abstract: The performance of SnO2/SiO2/n-Si solar cells was studied by considering various transport mechanisms including minority-carrier diffusion, carrier recombination, and tunneling through insulating layer. The tunneling current through the SiO2 layer was obtained by employing the Airy-wavefunction approach. The efficiency was calculated to determine the performance of the cells under AM1 illumination for different values of insulating layer thickness, interface state density, hole life-time, doping density of silicon substrate, and cell thickness. It was shown that the efficiency increases as the insulating layer becomes thinner due to the decrease of short-circuit current. It was also shown that the efficiency increases as the doping density increases up to 6x1022/m3 and it then decreases for higher doping densities. As the interface state density decreases, the efficiency becomes higher. In addition, the increases in the hole lifetime and cell thickness enhance the efficiency of the solar cell.

Abstract: In this paper, a comparative study of temperature effect which introduces a thermionic current under a high applied electric field, on three different modes of field emission current, such as Tunneling current, Fowler-Nordheim current and Field emission current in between these two regions has been done. Moreover, an idea of micromechanical displacement sensor with high sensitivity, operating in Fowler-Nordheim current mode, has been proposed. The displacement sensitivity of proposed sensor in Fowler-Nordheim current domain is about 10-9 m/A. The displacement sensitivity has been shifted from its expected value due to thermal effect (at 700K temperature) at about 1010V/m applied electric field across tip gap.

Abstract: The macroscopical breakage and nature change of material usually originate in nanometer scale, and the nature of some materials depends on temperature strongly. So it is extremely important for the research of heat transfer in micro-scale and nanometer technology to understand and control the influence of temperature on the nature of material, and developing advanced measuring technique can also improve our knowledge on theories involved in such problem. Due to the usage of variable-temperature sample stage, utilizable range of temperature is widely extended, and thus topography images of materials changing with temperature can be observed so that the thermal properties of materials can be studied further. Accordingly, the theoretical basis of heat-transfer and the influence of temperature on tunneling current owing to temperature variation should be presented. In the view of microscale heat-transfer, this paper describes the problem that heat current transfers from surface of sample to tip of probe through layer of air by means of Boltzmann theory, which can be expressed by the hyperbolic equation of heat conduction when the time is nearly equivalent to slack time and the scale is much larger than the characteristic scale of local thermodynamic equilibrium. The mode of heat-transfer on probe is also analyzed and the analytical solution is obtained in the paper. In addition, the influence of temperature increment of sample on tunneling current is discussed in detail and the change trend of tunneling current with temperature is also obtained in a limited temperature range. Due to such factors, which are possible to disturb the topography images of sample, there is no doubt that many difficulties will be brought to developing new technology such as detecting displacement and strain of materials at microscale by using the images of sample heated and unheated. To understand and control such factors has important advantage for making progress in the advanced scientific fields.