Evaluation of ambipolar potential barrier in the gas dynamic trap by Doppler spectroscopy

The recently developed Doppler spectroscopy diagnostic has been used to evaluate the height of the ambipolar potential barrier forming in the gas dynamic trap (GDT) plasma between the central cell and the region with a large magnetic expansion ratio beyond the mirror. The diagnostic technique based on the gas jet charge exchange target, allowed to measure the potential profile along the line of sight covering the radial range from the axis to the limiter. The on-axis potential drop was found to be 2.6÷3.1 in units of the central plane electron temperature, which supports the existing theoretical understanding of suppression of electron thermal conductivity in the GDT expander.

Method for Determining the Schottky Diodes Electrical Parameters

When studying the operation of Schottky diodes the most important electrical parameters are the height of the potential barrier, the coefficient of ideality, the saturation current and the series resistance of the material and contacts. These parameters can be determined from the experimental volt-ampere characteristics. The article considers the methods of determining these electrical parameters of Schottky diodes, as well as the factors that affect the accuracy of calculations. The existing methods for calculating the electrical parameters of Schottky diodes are analyzed, namely: the method of Norde, Roderick, Chong, Sato and the method of direct approximation. The Norde method was developed for a coefficient of ideality equal to one for cases where the effect of series resistance on the I–V characteristics makes a significant error in determining the barrier height by simpler methods. A significant disadvantage of this method is that in many cases the coefficient of ideality is not equal to one, even in the case of an ideal diode, which makes an error in the calculation result. The advantage of Roderick's method is the possibility of describing the forward and reverse branches of the I–V characteristics by one dependence, as well as taking into account measurements at voltages less than tripled temperature potential. The disadvantages of this method include the lack of consideration of the effect of series resistance, which may result in additional errors. The main advantage of the Chong method is the determination of the series resistance together with the height of the barrier and the coefficient of ideality, which not only provides additional information about the contact, but also convenient in terms of automation of the calculation process. The disadvantages include the possibility of applying the method only to the voltage range above the tripled temperature potential. The disadvantages of Sato methods and direct approximation include the fact that the calculation is performed at one point of the I–V curve, which can negatively affect the accuracy. It is also shown that these methods have a significant standard deviation of the calculated values from the experimental ones, which is due to the temperature dependence of the height of the potential barrier and the dependence of the coefficient of ideality on the voltage. Also, the reason for the increase in the calculation error of the electrical parameters in all five methods is the decrease in the length of the I–V characteristics in logarithmic coordinates. When using any of the considered methods, the calculation is performed in logarithmic coordinates, which complicates the determination of the boundaries of the I–V section, where the dependence of the parameters of the Schottky diode on the voltage is insignificant. A new algorithm for calculating the electrical parameters of Schottky diodes has been developed. Based on the conjugate gradient method, a method for optimizing the algorithm for calculating the electrical parameters of Schottky diodes was developed, which made it possible to reduce the standard deviation by more than an order of magnitude. The developed algorithm is verified by comparing the calculated volt-ampere characteristics of Schottky diodes with those obtained experimentally. To construct the calculated volt-ampere characteristics, the values of the electrical parameters of Schottky diodes were used, which were determined by the presented algorithm. The results of the calculation are in good agreement with the experimental data. The proposed method can be used both in scientific work to study the properties of semiconductor materials, and in production to control the quality of Schottky diodes.

DIAGNOSIS OF SEMICONDUCTOR HETEROSYSTEMS USING THE PHOTOVOLTAIC METHOD

The diagnostic method is as follows: the lateral photo-EMF spectral characteristics are measured, generated in the structure (or device) when illuminated by wavelength light with a near the edge of the basic semiconductor layer. For illustrations of efficiency method the given part of the measurement results for Schottky contact samples with a nitrogen concentration of 5% and a thermal annealing temperature of 900 and 950°C. It has been found that a significant character and a small amplitude of such a characteristic indicates qualitative at a homogeneity and the necessary magnitude of the potential barrier (or barriers), that it is necessary to form to make Schottky contact or other structure. A significant characteristic and a small amplitude of such a characteristic indicates a qualitative one-line and the required value of a potential barrier (or barriers) that must be formed for the manufacture of a semiconductor structure or device. If the spectral characteristic has one maximum and amplitude that is many times higher than the amplitude of a significant characteristic, then this indicates a formed transition layer between components of heterosystems with high, compared with a quasine-power region of semiconductor, conductivity. The presence of such a layer increases the probability breaks down of the microelectronic device. Investigation of the distribution of lateral photours along the metal semiconductor interface compliant interpretation of spectral characteristics features. The linear significant form of distribution of EMF confirms the presence of a transition layer with a lower doping level compared with GaAs. An important feature of the diagnostic method is its non-destructive character, as well as the possibility of applying to semiconductor or devices based on them, in which the photovoltaic effect may occur.

The Schwarzschild black hole in f(R) can exist superradiation phenomenon

For the relationship of the limit $y$ of the incident particle under the superradiance of the preset boundary (${\mu} = {y}{\omega}$),we find the relationship between black hole thermodynamics and superradiation, and use boundary conditions to establish the relationship between y and R. One of the modes under f(R) gravity,there is a possible solution.When r tends to infinity, as a coordinate transformation, y tends to 0. At that time, there is a potential barrier near the event horizon, that is, the Schwarzschild black hole under f(R) gravitation has superradiation at that time.

Light management with quantum nanostructured dots-in-host semiconductors

Insightful knowledge on quantum nanostructured materials is paramount to engineer and exploit their vast gamut of applications. Here, a formalism based on the single-band effective mass equation was developed to determine the light absorption of colloidal quantum dots (CQDs) embedded in a wider bandgap semiconductor host, employing only three parameters (dots/host potential barrier, effective mass, and QD size). It was ascertained how to tune such parameters to design the energy level structure and consequent optical response. Our findings show that the CQD size has the biggest effect on the number and energy of the confined levels, while the potential barrier causes a linear shift of their values. While smaller QDs allow wider energetic separation between levels (as desired for most quantum-based technologies), the larger dots with higher number of levels are those that exhibit the strongest absorption. Nevertheless, it was unprecedently shown that such quantum-enabled absorption coefficients can reach the levels (104–105 cm−1) of bulk semiconductors.

A Modelling of Tunnelling Current through a Trapezoidal Potential Barrier by Using Exponential Wavefunction Approach

A tunnelling current through a trapezoidal barrier potential has been modelled. The transmittance is determined using the exponential wavefunction approach method. Furthermore, the transmittance is used to calculate the tunnelling current density by applying the Gauss-Laguerre quadrature method. The simulation results show the increasing bias voltage causes the raising tunnelling current, and an increase of temperature is proportional to the tunnelling current.