Drift Velocity Of Charge Carriers Research Articles

Terahertz amplification and lasing by using transverse electric modes in a two-layer-graphene-dielectric waveguide structure with direct current

We study for the first time the interaction between the waveguide modes of graphene structure and freely propagating terahertz (THz) electromagnetic waves (this interaction takes place within the light cone). We revealed a new and rather unexpected physical phenomenon by showing that freely incident THz electromagnetic waves can resonate with the surface transverse electric (TE) modes of the graphene waveguide in virtue of these modes having their dispersions in the vicinity of the light cone. The dispersion and amplification of surface TE modes in a dielectric waveguide covered with two graphene layers biased by direct current (DC), as well the amplification and lasing of incident THz wave by excitation of TE mode resonances, are investigated. The DC flows perpendicular to the direction of the surface wave propagation and creates the capacitive complex conductivity of graphene at THz frequencies, which is necessary for the existence of surface TE modes in graphene. The real part of graphene conductivity can be negative at THz frequencies due to DC in graphene which leads to amplification and lasing of THz radiation. Such structure can be of great practical importance because an external THz wave can be amplified or generated in lasing process without using special coupling elements commonly needed for ensuring the interaction between external THz wave and surface waveguide modes. The use of a two-layer graphene structure makes it possible to reduce the charge–carrier drift velocity required for reaching the lasing threshold at those resonances, as compared to a structure with a single graphene layer.

Усиление терагерцовых электромагнитных волн в структуре с двумя слоями графена при протекании постоянного электрического тока: гидродинамическое приближение

The amplification of electromagnetic terahertz radiation in a structure with two layers of hydrodynamic graphene with a direct electric current is studied theoretically. The hydrodynamic conductivity of graphene is investigated. It is shown that the real part of the graphene conductivity can be negative in the terahertz frequency range at the drift velocities of charge carriers in graphene that are lower than the phase velocity of the electromagnetic wave. For small wavevectors of a terahertz wave incident on a graphene structure, the spatial dispersion insignificantly contributes to the hydrodynamic graphene conductivity. Because of this, the amplification efficiency does not depend on the direction of currents in each of the graphene layers. It is shown that graphene with direct electric current can be used to create THz amplifiers operating at room temperature.

Gas-Filled Gamma-Radiation Detector Based on High-Purity Xenon

This paper reports on the development, manufacturing and testing of proportional γ-ray detectors filled with gas mixtures based on high-purity xenon. To let the gas mixtures into the detector, a special installation was developed and manufactured, consisting of components designed to work with high-purity gases. The influence of the gas pressure, its composition (pure Xe or its mixture with H2, CH4), and the voltage at the anode on the spectrometric resolution and gas gain of the detectors was studied. The addition of H2 or CH4 to xenon is used to increase the charge carrier drift velocity. These additives also stabilize the gas mixture, i. e. decrease the probability of gas breakdown at high voltage between the detector electrodes. Gas xenon, as well as its mixtures, of research purity grade (99.9999%) have been used. Proportional γ-ray detectors based on xenon gas can operate in both counting and spectrometric modes. To study the characteristics of the detectors, we used standard sources of γ-radiation 241Am, 137Cs, 152Eu, 133Ba. The best energy resolution values to date were obtained for a detector filled with a gas mixture of Xe + 2.1% CH4 at a pressure of 2.5 bar and an anode voltage of 2500 V; they were ~ 9.5% for an energy of 40 keV and ~ 5% for 120 keV. In the manufacturing of detectors intended for radiation monitoring and identification of radioactive materials, in particular in nuclear power, complex materials science problems have been solved. To increase the thermal and radiation resistance, all elements of the detector construction are made of materials that are weakly activated by ionizing radiation. In addition, the design of the detectors is completely free of glass elements and organic components. The detectors are designed to monitor technological processes and to work as part of radiation monitoring systems, including those at nuclear power plants.

Locating events in a segment of a segmented HPGe detector at KRISS

Abstract A specific segment of the 24 fold segmented HPGe detector was studied for improving the interaction position resolution from several cm to mm. The segmented HPGe detector was modeled by CAD program with their electrodes which was isolated by the Boolean function. The Shockley-Ramo theorem changed the Gauss law to Laplace equation problem for calculating the induced charge on each electrode. Finite Element Method solved the Poisson and Laplace equation with their boundary conditions for Electric field and potential. The drift velocities of charge carriers were compared between both along the 100 > and one between 100 > and 110 > Ge crystal axis at a specific segment and used to simulate the pulse shapes with 1 mm position resolution. Coincidence system between a specific segment and 3 × 3 HPGe detector verified the simulated pulse shapes by comparing these with the experimental ones which are generated at the specific target region with a fixed scattering angle. The experimental and simulated ones were χ 2 fitted to find the least χ 2 value and locate the interaction positions. The interaction positions of experimental pulse shapes were analyzed statistically after the rise time correction along 100 > and 110 > Ge crystal axis. The position resolution as FWHM on x, y, and z axis is the 3.12, 4.38 and 8.69 mm with the collimator size 3, 6, and 6 mm, respectively.

Study the Electronic Transport Properties for InAs0.3P0.7 the First Derived Substrate from InP via Monte Carlo Methods

This paper compares the electronic transport proprieties of two materials, InP and InAs0.3P0.7, in order to present the advantageous characteristics of InAs0.3P0.7 and which in turn leads to inventing of a first substrate derived from InP. This comparative study is performed by using Monte Carlo methods at room temperature and includes the acoustic, polar and inter-valley scattering mechanisms, as well as the energy and drift velocity of charge carriers. The obtained results show that InAs0.3P0.7 presents better behavior in terms of charge carrier energy and drift velocity compared to InP, due to its low set energy describing the band energy of InAs0.3P0.7, as well as high atomic density. On the other hand, the registered energy saturation for charges carriers in the case of InAs0.3P0.7 is reached quickly and under lower applied electric fields compared to InP, due to its high rate of scattering, making InAs0.3P0.7 better than InP for use in high-frequency and low-power operation applications.

Valley-polarized magnetoconductivity and particle-hole symmetry breaking in a periodically modulated α−T3 lattice

We explore the transport properties of a periodically modulated $\alpha$-$\mathcal{T}_3$ lattice in the presence of a perpendicular magnetic field. The effect of the Berry phase on electrical conductivity oscillation, so-called Weiss oscillation, caused by the modulation induced non-zero drift velocity of charge carriers is investigated. Employing linear response theory within the low temperature regime, we analyze Weiss oscillation as a function of the external magnetic field for both electrically and magnetically modulated $\alpha$-$\mathcal{T}_3$ lattice numerically as well as analytically. The Berry phase makes this hexagonal lattice structure behave differently than other two-dimensional fermionic systems. It causes a significant valley polarization in magnetoconductivity. Most interestingly, the combined effect of both modulations breaks the particle-hole symmetry and causes a smooth transition from even (odd) to odd (even) filling fraction corresponding to the density of states peaks by means of the Berry phase.

Surface plasmon polariton amplification in semiconductor–graphene–dielectric structure

A mechanism of amplification of surface plasmon polaritons due to the transfer of electromagnetic energy from a drift current wave into a far‐infrared surface wave propagating along a semiconductor‐dielectric boundary in waveguide geometry is proposed. A necessary condition of the interaction of these waves is phase matching condition, i. e., when the phase velocity of the surface wave approaches the drift velocity of charge carriers. It is shown that in the spectral region of the surface plasmon polariton slowing‐down its amplification coefficient can reach values substantially exceeding the ohmic loss coefficient of the surface wave in the structure. image

Numerical Drift-Diffusion Simulation of GaAs p-i-n and Schottky-Barrier Photodiodes for High-Speed AIIIBV On-Chip Optical Interconnections

In this paper, we consider the problem of the research and development of high-speed semiconductor photodetectors suitable for operation as parts of on-chip optical interconnections together with the high-speed laser modulators based on the AIIIBV nanoheterostructures. This research is aimed at the development of the models and modelling aids designed for the simulation of carrier transport and accumulation processes taking place in on-chip photosensitive devices during the detection of subpicosecond laser pulses. Another aim of the paper is to apply the aforementioned aids for the investigation of GaAs p-i-n and Schottky-barrier photodiodes. We propose the non-stationary drift-diffusion models, an original numerical simulation technique and the applied software allowing one to simulate the photosensitive devices with different electrophysical, constructive and technological parameters. We have taken into account different kinds of carrier generation and recombination processes, the effects of electron intervalley transition and carrier drift velocity saturation in order to improve the simulation results’ adequacy. We have concluded that the influence of these effects on the performance of photodetectors for on-chip optical interconnections is significant. The response time of GaAs p-i-n and Schottky-barrier photodiodes calculated taking into account the drift velocity dependence on electric field intensity is insufficient for the adequate detection of subpicosecond laser pulses. According to the simulation results, it is reasonable to develop the methods aimed at the increase in the drift velocity of charge carriers in the photodetector active region by means of built-in electric field reduction.

RETRACTED ARTICLE: Effect of the electric current on the Casimir force between graphene sheets

The dependence of the thermal component of the Casimir force and Casimir friction between graphene sheets on the drift velocity of charge carriers in one of the sheets has been analyzed. It has been shown that the drift motion results in the measurable change in the thermal Casimir force owing to the Doppler effect. The thermal Casimir force, as well as Casimir friction, increases strongly in the case of resonant photon tunneling, when the energy of an emitted photon coincides with the excitation energy of an electron-hole pair. In the case of resonant photon tunneling, the dominant contribution to the Casimir friction even at temperatures above room temperature comes from quantum friction caused by quantum fluctuations. Quantum friction can be detected in an experiment on the friction drag between graphene sheets in a high electric field.

Hopping conduction in strong electric fields: Negative differential conductivity

Effects of strong electric fields on hopping conductivity are studied theoretically. Monte Carlo computer simulations show that the analytical theory of Nguyen and Shklovskii [Solid State Commun. 38, 99 (1981)] provides an accurate description of hopping transport in the limit of very high electric fields and low concentrations of charge carriers as compared to the concentration of localization sites and also at the relative concentration of carriers equal to 0.5. At intermediate concentrations of carriers between 0.1 and 0.5, computer simulations evidence essential deviations from the results of the existing analytical theories. The theory of Nguyen and Shklovskii also predicts a negative differential hopping conductivity at high electric fields. Our numerical calculations confirm this prediction qualitatively. However the field dependence of the drift velocity of charge carriers obtained numerically differs essentially from the one predicted so far. Analytical theory is further developed so that its agreement with numerical results is essentially improved.

Development of Layered Type Single Crystalline Diamond Radiation Detector as an Energy Spectrometer

Radiation detectors were fabricated with layered structure diamonds comprising several micrometers of a boron-doped single crystal diamond and 20 μm of insulating single crystal diamond layers grown on a HP/HT-type Ib diamond single crystal substrate. To improve the yield rate of CVD diamond radiation detectors this approach was adopted. The detectors had rectification characteristics because of their boron-doped diamond contact and aluminum Schottky contact. The leakage current of one detector was less than 0.2 pA at reversed bias voltage of +50 V. Energy resolutions of 2.6% and 2.8% for alpha particles from 241 Am were achieved using these detectors. The rise time of a leading edge of an output signal from one detector was less than 20 ns, which was the fastest rise time of the measurement system; drift velocities of charge carriers were estimated to be faster than 1 × 105 cm/s. In addition, cathode luminescence spectra of insulating diamond layers were measured; peaks caused by free exciton recombination and ‘band A’ were observed. Improved crystallinity of the boron-doped diamond layer helps realization of a layered-type diamond radiation detector with higher energy resolution.

The Cyclotron Waves in Layered Conductors

We have studied theoretically the propagation of electromagnetic waves in layered conductors placed in a strong magnetic field B 0. It is shown that the wave process is very sensitive to the orientation of B 0 with respect to the layers. The weakly damping modes with the frequencies near the cyclotron resonance frequency can propagate at orientations of the magnetic field vector, for which the drift velocity of charge carriers along the B 0-direction is close to zero. The cyclotron waves spectrum is analyzed with regard to the Fermi-liquid interaction of electrons.

Saturation drift velocity measurement for CVD diamond by combination of a charge distribution measurement and a TOF method using a UV pulsed laser

Drift velocities of charge carriers in polycrystalline diamonds were measured by a self-triggered time-of-flight (TOF) method with alpha particles based on a radiation measurement technique. Based on these measured results, a synthesis method for polycrystalline diamond was verified, and the electric properties of polycrystalline diamonds were improved; drift velocity was increased from 5 × 10 2 to 3 × 10 4 cm/s. The mean free paths (MFPs) of capture of charge carriers in a CVD single crystal diamond was obtained by induced charge distribution measurements with alpha particles, and drift velocity was measured by another TOF method using a UV pulsed laser. MFPs of capture of electron and hole in a CVD single crystal diamond were determined to be 5.4 and 9.6 μm, respectively; the hole and electron drift velocities were 5 × 10 5 cm/s and 3 × 10 5 cm/s in an electric field of 24.4 kV/cm, respectively. For diamond, short transit times of several nanoseconds and short MFPs of capture in several micrometers were successfully obtained for the first time by combining of these methods.

The influence of anisotropic electron drift velocity on the signal shapes of closed-end HPGe detectors

This study is concerned with the anisotropy of the electron drift velocity in germanium crystals at high electric fields and low temperature, and its influence on the charge collection process in n-type, high-purity germanium (HPGe) detectors of closed-end, coaxial geometry. The electron trajectories inside HPGe detectors are simulated using a phenomenological model to calculate the dependence of the drift velocity on the angle between the electric field and the crystal orientation. The resulting induced currents and pulse shapes for a given detector geometry and preamplifier bandwidth are compared to experiment. Experimentally, the dependence of the pulse shapes on the conductivity anisotropy in closed-end HPGe detectors was observed. The experimental data on pulse shapes were obtained by sampling preamplifier signals of an encapsulated, hexaconical EUROBALL detector, which was irradiated by collimated 22 Na and 241 Am sources. The crystal orientation was measured by neutron reflection. Qualitative agreement between the simulated and experimental pulse shapes was found. A variation in the charge collection time of up to 50 ns was observed for different drift directions of the carriers relative to the crystal orientation. Furthermore, a deflection of the trajectories from a straight radial drift direction of about 20° was predicted by the simulations. These two main effects of charge carrier drift velocity anisotropy in coaxial Ge detectors are expected to play an important role in the development of γ-ray tracking detectors.

A pulsed corona-Townsend method for measurement of electron/ion number ratios and drift velocities

A new, easily-implemented method based on the pulsed-Townsend technique has been developed to measure drift velocities of charge carriers in a corona discharge at atmospheric pressure. The method also yields the electron/ion number ratio and an upper limit on the value of the electron attachment coefficient. Approximate electron drift velocities measured in nitrogen are in agreement with known values. In addition, the negative ion mobility obtained in nitrogen containing small amounts (0-3.7%) of oxygen agrees with known data. Therefore the pulsed corona-Townsend technique can be used to obtain data in gas mixtures of practical interest. The method can also distinguish the charge carriers in a corona discharge. This is especially useful in nonelectronegative gases with unknown concentrations of electronegative impurities.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Photoconductivity of a semiconductor with a transverse gradient of drift velocity of charge carriers

The spectral photosensitivity of a semiconductor with a gradient of the drift velocity of charge carriers has been investigated. It was found to be of either selective or bolometric type depending on mutual directions of incident light and of the gradient. Photoconductivity of germanium samples of ringlike geometry was studied experimentally over the spectral range 0.8–2.2 μm at room temperature. The main results are: decay of the photocurrent in a semiconductor where the gradient differs from the exponential one and depends on the mutual directions of the gradient and diffusion of carriers; the amplitude of the photocurrent depends not only on the typical parameters but on light direction and also gradient; determination of both effective lifetime of carriers and the bandgap by the Moss method is not valid for a semiconductor with a gradient of drift velocity; a photodetector with parameters reversibly controlled by an electric field is possible.

Acoustoelectric effects in a gaseous medium.

The well-known acoustoelectric coupling effect in semiconductors, whereby a sound wave is amplified if a charge carrier's drift velocity exceeds the speed of sound, also exists for ions and electrons in a gaseous medium, but theoretical analysis so far has been limited to simplified collisional-exchange models [G. M. Sessler, Phys. Fluids 7, 90 (1964); U. Ingard and M. Schultz, Phys. Rev. 158, 106 (1967); T. D. Mantei and M. Fitaire, in 2 Proceedings of the 10th International Conference on Phenomena in Ionized Gases (Oxford University Press, Oxford, 1971), p. 309]. The present paper is based upon more accurate considerations of collisional phenomena, leading to more realistic predictions of the qualitative and quantitative nature of the effect.

Time evolution of the phonon and ionized impurity limited 2D hot carrier distribution function in a n-GaAs square quantum well (QW)

The time evolution of the distribution function of hot electrons interacting with ionized impurities, acoustic and polar optical phonons is studied in terms of the Boltzmann integral equation. The calculated distribution functions are used to determine the charge carrier drift velocity, the average energy as well as the average momentum and energy loss rates as a function of time at constant values of the lattice temperature and charge carrier density. The stationary non-equilibrium values of these quantities are found to be established after 3–4 ps.

Exploiting the drift velocity of charge carriers

Exploiting the drift velocity of charge carriers

Field-dependent grain boundary barriers as a cause of carrier drift velocity saturation in organic solids

The aim of this communication is to present an alternative interpretation of low-field charge carrier drift velocity saturation in polycrystalline organic solids. It is assumed that the above effect is due to grain barriers. In the materials under study, thermal generation of charge carriers is negligible. Therefore the charging of grain barriers is due to the carriers injected, and in the case of electrode injection is dependent on the field applied. The consequences of the above ideas as well as comparison with experiment is presented.