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Carbon Nanotube Electronics
Published in Ann Rose Abraham, Soney C. George, A. K. Haghi, Carbon Nanotubes, 2023
A potential barrier exists at every contact between metal and semiconductor. This is known as the Schottky barrier. In this device, source and drain terminals are metals and the terminal contact between metal and nanotube has a Schottky barrier. Working principle is based on direct tunneling through this barrier at source–channel junction. Transconductance is gate voltage-dependent as the barrier width is controlled by this voltage. With increase in gate bias, barrier width decreases which further increase in quantum mechanical tunneling and current flow in the transistor channel. Occurrence of ambipolar conduction at low gate oxide thickness is a major setback. This can lead to exponential increase in leakage current. Increase in gate oxide thickness reduces the leakage current as well as improves the performance. Asymmetric gate oxide is another alternative solution. Other drawbacks include limited channel length leading to increased source to drain tunneling and inability to place gate and source close by as this leads to increased parasitic capacitance. The schematic diagram of the design is given in Figure 9.8.
Photodetector Fundamentals
Published in Joachim Piprek, Handbook of Optoelectronic Device Modeling and Simulation, 2017
A contact between a metal and a semiconductor may be either ohmic or rectifying. To obtain a rectifying contact, a certain combination of metal and a given semiconductor is needed. In such a junction, potential barrier develops due to the difference between the work functions of the metal and semiconductor. Another difference between a p-n junction and an SB diode is that both electrons and holes contribute to the current in a p-n junction, whereas SB diodes are majority carrier devices. The MSM PD consists of two junctions, both of which may be rectifying or one junction ohmic and the other rectifying. The band diagram of an MSM PD is shown in Figure 35.14, in which the potential barrier ϕb is due to the work function difference. The two electrodes are connected serially, back-to-back, and the device contains two diodes as shown in Figure 35.14.
Relativistic Quantum Transport
Published in David K. Ferry, An Introduction to Quantum Transport in Semiconductors, 2017
In classical semiconductors, which possess a sizable bandgap, a potential barrier higher than the energy of the incident particle generally blocks transmission of the particle through the barrier. This is because the potential V – E, where E is the energy of the incident carrier, lowers the energy into the bandgap, where there are no propagating wave solutions. However, if the barrier has a finite thickness, then it is possible for the particle to tunnel through the barrier [31]. This is because with the wave interpretation, the part of the wave that penetrates the potential barrier does not fully decay before the back edge of the barrier is reached. Nevertheless, the transmission probability decays exponentially both with the height of the potential barrier and with its thickness. In the relativistic world of graphene, however, the barrier pushes the incident electron wave energy into the valence band, where there are allowed states. Nevertheless, the particle cannot transit the potential barrier (of infinite thickness) because the electron and hole states have different chirality, so the particle is still reflected. If the barrier has finite thickness, we come to the Klein paradox, which leads to a situation in which an incoming electron can penetrate a potential barrier if the height exceeds the rest energy mc2 [32]. In graphene, the rest energy is zero, so that Klein tunneling can occur whatever the incident energy of the particle. When this happens, the transparency of the barrier depends only weakly on the barrier height and actually increases as the barrier height increases. The physics of the process is that the penetrating electron can couple to holes (positrons) under the barrier to affect the transmission, and matching between the two sets of wavefunctions leads to the high transparency [33].
Effects of applied magnetic field and pressure on the diamagnetic susceptibility and binding energy of donor impurity in GaAs quantum dot considering the non-parabolicity model’s influence
Published in Philosophical Magazine, 2023
Ibrahim Maouhoubi, Redouane En-nadir, Kamal El bekkari, Izeddine Zorkani, Abdallah Ouazzani Tayebi Hassani, Anouar Jorio
Within the effective-mass approximation, the Hamiltonian for a shallow-donor impurity (D) placed inside of a symmetrical QDisk made out GaAs surrounded by a wide band-gap semiconductor that forces the particle to remain confined inside the GaAs material (infinite potential barrier) is given as follows: where r0 and are the electron-impurity position and relative dielectric constant of the material, respectively. is the magnetic-field potential and is the confining potential barrier in polar coordinates. m* is the effective electron mass given as follows. For a uniform magnetic field, we can write (for a symmetric gauge ), where . The introduction of the impurity into the system makes it impossible to analytically solve the Schrodinger equation, therefore, it is necessary to use the variational method. Equation (1) is given in atomic unit as:
Mean first passage time of active Brownian particle in one dimension
Published in Molecular Physics, 2018
Mean first passage time (MFPT) of a diffusing Brownian particle is a heavily researched problem. Recently, MFPT has been studied in context of active Brownian particles (ABPs) which under go self-propulsion in addition to the Brownian motion [1]. An ABP performs persistent motion along the direction of an embedded unit vector which performs rotational diffusion. Often, the motion of ABPs is modelled on a coarse grained level by averaging out the orientational degree of freedom [2,3], resulting in a non-Markovian equation of motion. Following this approach, the authors in Ref. [1] studied the MFPT of an ABP diffusing in an external potential. In this paper, we preserve the orientational degree of freedom of the active particle and obtain its MFPT in one dimension. This allows us to verify the validity and accuracy of the coarse graining approach. We obtain the MFPT of an ABP in two scenarios, (a) freely diffusing ABP with stochastic resetting and (b) escape of an ABP over a potential barrier. For both of these scenarios, we benchmark our findings with existing literature.
Simulation-based analysis of an L-patterned negative-capacitance dual tunnel VTFET
Published in International Journal of Electronics, 2023
Girdhar Gopal, Harshit Agrawal, Heerak Garg, Tarun Varma
is the gate voltage at which and . Similarly, is the gate voltage at which and and DIBL was determined using Equation 9 and was found to be 95 mV/V. The drain-induced barrier rising effect (DIBRE) is obtained with a negative capacitance that enhances at large VDS and gives us the reverse of DIBL. The potential barrier increases with drain voltage. This DIBR explains the negative capacitance behaviour.