Current Carrier Concentration Research Articles

Electronic Structure and Transport Properties of Bi2Te3 and Bi2Se3 Single Crystals.

The electrical resistivity and the Hall effect of topological insulator Bi2Te3 and Bi2Se3 single crystals were studied in the temperature range from 4.2 to 300 K and in magnetic fields up to 10 T. Theoretical calculations of the electronic structure of these compounds were carried out in density functional approach, taking into account spin-orbit coupling and crystal structure data for temperatures of 5, 50 and 300 K. A clear correlation was found between the density of electronic states at the Fermi level and the current carrier concentration. In the case of Bi2Te3, the density of states at the Fermi level and the current carrier concentration increase with increasing temperature, from 0.296 states eV-1 cell-1 (5 K) to 0.307 states eV-1 cell-1 (300 K) and from 0.9 × 1019 cm-3 (5 K) to 2.6 × 1019 cm-3 (300 K), respectively. On the contrary, in the case of Bi2Se3, the density of states decreases with increasing temperature, from 0.201 states eV-1 cell-1 (5 K) to 0.198 states eV-1 cell-1 (300 K), and, as a consequence, the charge carrier concentration also decreases from 2.94 × 1019 cm-3 (5 K) to 2.81 × 1019 cm-3 (300 K).

Conductivity versus structure dependence investigation of Na1+xZr2SixP3-xO12 (0 ≤ x ≤ 3) through composition optimization by adjusting Si/P ratio

Presently, the low ionic conductivity of Na super ionic conductor (NASICON) electrolytes is one of the main obstacles to the development of solid-state sodium batteries. Most researchers focus on the modified NASICON by doping with foreign elements and have not paid much attention to the effect of the composition changing by adjusting the ratio of elements in Na1+xZr2SixP3-xO12 (0 ≤ x ≤ 3) on the ionic conductivity. In order to clarify the relationship between the ionic conductivity and the structure/composition of Na1+xZr2SixP3-xO12, the ionic conductivity dependence on the Si/P ratio is systematically investigated in this study. The obtained results demonstrate that the ionic conductivity variation of NASICON is close to an order of magnitude i.e. the ionic conductivity of Na1+xZr2SixP3-xO12 is much more sensitive to the Si/P ratio in the structure. This means that it is crucial to control the composition during the preparation process to obtain the electrolyte with high ionic conductivity. The strong composition-dependent property of Na1+xZr2SixP3-xO12 can be attributed to the change of current carrier concentration, crystal structure, and sintering property resulting from the Si/P ratio. The results are insightful for further understanding the conducting characteristics of Na1+xZr2SixP3-xO12 material and its derivatives.

Gettering of epitaxial indium arsenide by the rare earth element holmium

The results of a study of the galvanomagnetic properties of indium arsenide grown by liquid-phase epitaxy are presented. It is shown that the use of the rare earth element holmium in the growth of InAs epitaxial layers makes it possible to reduce the electron concentration by two orders of magnitude to n=2.1·1015 cm-3 at T=77 K. This effect is due to the gettering of shallow background impurities with the formation of their compounds in the melt. With an increase in the holmium content of more than 0.12 mol.% the concentration of current carriers in the material begins to increase, while mobility decreases due to the influence of VAs-Ho donor centers. This method of gettering is promising for obtaining A3B5 materials with a low concentration of current carriers, which are in demand in the optoelectronic industry. Keywords: indium arsenide, rare earth element, Hall coefficient, concentration of current carriers, mobility of current carriers.

Геттерирование эпитаксиального арсенида индия редкоземельным элементом гольмием

The results of a study of the galvanomagnetic properties of indium arsenide grown by liquid-phase epitaxy are presented. It is shown that the use of the rare earth element holmium in the growth of InAs epitaxial layers makes it possible to reduce the electron concentration by two orders of magnitude to n=2.1•1015 cm−3 at T=77 K. This effect is due to the gettering of shallow background impurities with the formation of their compounds in the melt. With an increase in the holmium content of more than 0.12 mol.% the concentration of current carriers in the material begins to increase, while mobility decreases due to the influence of VAs – Ho donor centers. This method of gettering is promising for obtaining AIIIBV materials with a low concentration of current carriers, which are in demand in the optoelectronic industry.

Synthesis and electrophysical properties of CdS/ZnTe heterojunctions

In this paper results of studying CdS/ZnTe heterostructures synthesized by the quasi-closed space sublimation method on glass substrates coated with an ITO layer are described. The electrical and photoelectric properties of the structures are studied using current–voltage and capacitance–voltage characteristics in a temperature range of 30–100 °C. Analysis of the experimental data shows that the main specific feature of CdS/ZnTe structures is the formation of a high-resistance transition layer, which affects the separation of carriers at the barrier contact. The current carrier concentration in the space charge region, which is determined from the capacitance–voltage characteristics, is 1 x 1015 cm-3; this fact suggests that one of the contacting materials—ZnTe—exhibits a high resistivity. Measurements of current–voltage characteristics in the solar cell mode give the following photoelectric parameters: open circuit voltage (UOC = 0.53 V, JSC = 27–30 A/cm2, and FF = 0.25.

Theoretical investigation of permeable segmented generator thermoelement on the base of Bi-Te, Pb-Te, Si-Ge

Results of computer study on permeable segmented generator thermoelement under efficiency-optimal operating conditions are set forth. Method for solving a multi-parameter optimization problem is described. Heat carrier flow rate, electric current density, parameters of current carrier concentration in each leg segment whereby energy conversion process is maximum thermodynamically efficient are determined. The results of research on a permeable segmented generator thermoelement based on Ві-Те, Pb-Te, PbTeG, Si-Ge materlals are presented. Comparison to conventional thermoelements showed the possibility of efficiency increase by 30 – 40% and generated power by 20-30%.

Electrophysical Properties of Monocrystalline n-Si+0.4at%Ge:P Alloy irradiated by 60Co Gamma Photons

In the monocrystal n-Si+0.4at.%Ge:P alloy irradiated with 60Co gamma photons non-monotonic changes in electrical resistance, current carrier concentration and mobility were detected by isochronal annealing at a temperature range of 20-400°C. The contribution of current transformations in the structure of radiation defects (PV, VO, VO2, CiCs, CiOi) to the temperature changes of electrical characteristics is analyzed. n-p conversion was detected at the critical temperature (~100°C) of isochronal annealing. Dissociation of PV centers and formation of electrically active VO centers were detected in the 120-150°C range. As a result, the concentration of current carriers increases. At elevated temperatures (> 150°C) non-monotonic changes in electrical characteristics are observed.The paper analyzes the contribution of Ge to the anomalous temperature changes of the electrophysical characteristics of the n-SiGe alloy.

Effekt of adsorbed Ge atoms on the photoemission properties of GaAs

A3B5 semiconductor compounds in the future are the most promising for further detailed consideration. In this regard, gallium arsenide is a semiconductor compound formed by elements of groups III and V of the periodic system – gallium Ga and arsenic As. Gallium arsenide and its surface properties attract much attention of researchers due to the possibility of its wide application in micro- and nanoelectronics technology. Despite numerous studies of the surface of semiconductors, many issues related to its properties and processes at the interface between two phases remain insufficiently clarified, especially in terms of the effect of the surface state on the energy spectrum of electrons in crystals. Interest in these issues is constantly growing not only from a scientific point of view, but also from a practical one, in connection with the development of semiconductor micro- and nanotechnologies. The development of its sections such as thin-layer nanoelectronics and optoelectronics, devices with MIS structures and charge coupling, cold cathodes and efficient photocathodes require an understanding of the processes in the near-surface layer of a semiconductor both with a free surface and with this free surface during the adsorption of other substances on it. This is also important for elucidating the possibility of changing the surface and near-surface properties of solids in a quite definite way. Gallium arsenide is the closest binary analog of germanium. By introducing appropriate impurities, gallium arsenide can be obtained with both n-type and p-type conductivity with different current carrier concentrations. This structure belongs to the crystallographic class of the cubic system, like germanium. Gallium arsenide and germanium crystallize in the structure of zinc blende. In view of the foregoing, it is interesting to study the influence of adsorbed germanium layers on the surface properties of gallium arsenide single crystals of various types of conductivity by photoemission method in ultrahigh vacuum. The questions of the influence of these coatings not only on the emission properties of gallium arsenide single crystals, but also the influence of these adsorbed germanium atoms on the energy structure in the near-surface region of single crystals are considered.

Hole transport and current–voltage characteristics of PEO/PVP/cobalt nitrate polymer blend electrolytes

AbstractHole transport properties and Current–Voltage characteristics of the single‐layer device in an inverted structure were investigated with spin‐coated PEO/PVP/Cobalt nitrate polyblend electrolyte film as an active layer. A strong correlation between morphology and ionic conductivity was confirmed through XRD, DSC‐TGA, SEM and fluorescence spectroscopic techniques. The optical band gap values are in good agreement with the electrochemical band gap. Schottky diode measurements confirmed the formation of p‐type semiconductors with PEO/PVP bulk films with cobalt nitrate as a dopant at room temperature. The I‐V characteristics are strongly dependent on the salt concentration in the polymer blend. The parameters of diodes such as barrier height, saturation current, and charge carrier concentration were calculated from I‐V characteristics. From C‐V characteristics a charge carrier concentration in the range of 1022 cm−3 was obtained for the highest concentration of cobalt nitrate salt in the PEO/PVP blend. A very low energy barrier for hole injection at the anode ΔEh = 0.28 eV was observed.

Numerical analysis of the radiation-induced conductivity in polymers in a large-signal regime

We made numerical calculations of the radiation-induced conductivity by computing current densities, carrier concentrations, and internal electric fields in a disordered sample biased by constant applied voltage under a pulsed or step-function irradiation in a large-signal regime. For this purpose, we used the multiple trapping model featuring an exponential trap distribution with the dispersion parameter α. Calculations of radiation-induced conductivity were done with traditional simplifications (1D-analysis, one-carrier polymer, diffusion currents neglected, and non-injecting electrodes). The nonlinear effects accompanying the large-signal radiation-induced conductivity, such as an internal field variation, the bimolecular recombination, and the charge carrier extraction by electrodes, have been consistently accounted for. Numerical analysis agrees satisfactorily with the results of previously published analytical calculations.

INVESTIGATION OF SENSITIVE ELEMENTS OF TEMPERATURE TRANSDUCERS BASED ON THERMOMETRIC MATERIAL Lu1-xScxNiSb

INVESTIGATION OF SENSITIVE ELEMENTS OF TEMPERATURE TRANSDUCERS BASED ON THERMOMETRIC MATERIAL Lu1-xScxNiSb

Электронная зонная структура и термоэлектрические характеристики SrTiO-=SUB=-3-=/SUB=-, BaTiO-=SUB=-3-=/SUB=- и CaTiO-=SUB=-3-=/SUB=-: ab initio подход

The calculations of Seebeck’s coefficient, conductivity and power functions for the electron-doped SrTiO_3, BaTiO_3 and CaTiO_3 compounds have been performed depending on temperature and current carrier concentration by employing ab initio method based on the electron density functional theory, on the Frohlich’s approach for the electron-phonon interaction and on the theory of Boltzmann–Onsager for the thermoelectric properties. The calculated Seebeck’s coefficient and conductivity correspond to experimental data. It is shown that for SrTiO_3 and BaTiO_3 the dependencies of power functions on the carrier concentration have maxima in the range of (200–250) × 10^{19} cm^{–3} at any temperature, while for CaTiO_3 the maxima are typical only at temperatures below 500 K. The temperature dependencies of the power function also confirm that such carrier concentration range is favorable for achieving high values of the SrTiO_3 figure of merit, while the maximally possible carrier concentration is necessary for optimal CaTiO_3 figure of merit.

Electronic band structure and thermoelectric properties of SrTiO-=SUB=-3-=/SUB=-, BaTiO-=SUB=-3-=/SUB=- and CaTiO-=SUB=-3-=/SUB=-: ab initio approach

The calculations of Seebeck's coefficient, conductivity and power functions for the electron-doped SrTiO3, BaTiO3 and CaTiO3 compounds have been performed depending on temperature and current carrier concentration by employing ab initio method based on the electron density functional theory, on the Frohlich's approach for the electron-phonon interaction and on the theory of Boltzmann--Onsager for the thermoelectric properties. The calculated Seebeck's coefficient and conductivity correspond to experimental data. It is shown that for SrTiO3 and BaTiO3 the dependencies of power functions on the carrier concentration have maxima in the range of (200-250)·1019 cm-3 at any temperature, while for CaTiO3 the maxima are typical only at temperatures below 500 K. The temperature dependencies of the power function also confirm that such carrier concentration range is favorable for achieving high values of the SrTiO3 figure of merit, while the maximally possible carrier concentration is necessary for optimal CaTiO3 figure of merit. Keywords: Ca, Sr, Ba titanates, PAW method, electronic structure, thermoelectric properties.

Effect of heat treatment on the galvanomagnetic properties of bulk nanostructured samples of Bi85Sb15 solid solution

Extruded bulk nanostructured samples of Bi85Sb15 solid solution from particles with average sizes ∼ 2.105; 950; 650; 380; 30 and 15 nm were obtained and investigated their galvanomagnetic properties in the range of ∼ 77-300 K. Were investigated samples that have not passed heat treatment, and the same samples that have passed heat treatment. It was found that the electrical and thermal properties of Bi85Sb15 solid solution samples significantly depend on the size of nanoparticles and post-extrusion heat treatment. Heat treatment leads to a decrease in the concentration of current carriers and to an increase in the mobility of current carriers and the total thermal conductivity of the samples under study, which is mainly due to the electronic component of thermal conductivity. The change in thermal parameters is satisfactorily explained by changes in occurring in the structure of samples during extrusion and heat treatment and correlates well with changes in the electrical parameters of these processes.

Interface control and electron transport in ALD ZnO/Al2O3 TFTs studied by gated Hall effect

Many challenges exist in understanding transport properties in metal-oxide thin film transistors (MO-TFTs). Microstructural disorder, dielectric/active layer interface trap states, and grain boundaries contribute to reductions in device properties such as transistor output current, mobility, and sheet carrier concentration. In this work, we use scheduled interruptions during atomic layer deposition combined with a series of thermal anneals to control properties of ZnO/ TFTs, and to experimentally decouple physical effects within the TFT affecting device performance. Using concurrent current–voltage and gated Hall effect measurements, we observe two sets of trends for these devices. In the first, increasing post-temperature anneal is shown to improve the device characteristics by reducing grain boundary effects. In the second, exposure to ambient conditions is shown to increase the number of interface trap states. Comparisons of measured values show that these trap states enhance some properties of the lower temperature annealed series, while degrading these values in the higher temperature annealed series. We show that this is due to devices acting in two separate transport regimes: localized, and non-localized. We investigate the position of the Fermi level, adjusted by gate bias, to these two regimes under each test condition, and suggest a simple model to describe the results.

Electrical properties of strained germanium nanofilm

Dependences of the concentration of intrinsic current carriers, electron and hole mobilities and specific conductivity for strained germanium nanofilms grown on the Si, Ge(0,64)Si(0,36) and Ge(0,9)Si(0,1) substrates with crystallographic orientation (001), on their thickness at different temperatures were calculated on the basis of the statistics of non-degenerate two-dimensional electron and hole gas in semiconductors. The electrical properties of such nanofilms are determined by the peculiarities of their band structure. It is established that the effects of dimensional quantization, the probability of which increases with decreasing temperature, become significant for germanium nanofilms with the thickness of d<7 nm. The presence of such effects explains the significant increase in the specific conductivity and the decrease in the intrinsic concentration of current carriers for these nanofilms. The electron and hole mobility in the investigated germanium nanofilms is lower in relation to such unstrained nanofilms. Only for the strained germanium nanofilm with the thickness of d> 50 nm grown on the Ge(0,9)Si(0,1) substrate, an increase in the hole mobility at room temperature of more than 1.5 times was obtained. The obtained results of the electrical properties of strained germanium nanofilms can be used in producing on their basis new elements of nanoelectronic.

Моделирование методом Монте – Карло кинетических явлений в твердых телах с использованием технологии параллельных вычислений OpenACC

The development of a software package using the OpenACC parallel computing technology for Monte Carlo simulation of the kinetic coefficients of homogeneous semiconductor materials is presented. The package is a set of interconnected classes, the parameters of the material and external fields are redefined in the child classes available to the user, which makes it possible to model a wide range of materials. The package allows us to use models of elastic (acoustic phonons, charged impurities) and inelastic (polar and nonpolar optical phonons) electron scattering in the single-band approximation. The use of OpenACC technology makes it possible to use both shared memory systems and hybrid systems equipped with graphics processors as a computing platform. The possibility of saving data about each particle at each time step of the simulation is provided. It allowed, in particular, to trace the dependence of the average collision frequency of the energy of charge carriers and strength of the DC electric field applied to the sample, in the beta-modification of gallium oxide, to assess the applicability of the conductivity models offered by other research groups. It is shown that the greatest contribution to the conductivity of the beta modification of gallium oxide at room temperatures is made by the scattering of electrons on polar optical phonons, and the average collision frequency, as well as the percentage of collisions of an electron with various types of inhomogeneities of the crystal lattice, weakly depend on the strength of the constant electric field. At a temperature of about 100 K, with an increase in the constant electric field applied to the sample, firstly, the proportion of scattering with the emission of polar optical phonons increases significantly and the proportion of scattering on charged impurities decreases, and secondly, the total frequency of collisions increases. This is due, on the one hand, to the heating of the electron gas by an electric field and the activation of scattering channels with the emission of a phonon at a given temperature, on the other hand, to an insufficiently rapid increase in the concentration of current carriers due to the ionization of impurities. Thanks to the Monte Carlo simulation, it was possible to directly evaluate the validity of the use of the Farvaque correction for an approximate description of the processes of inelastic electron scattering on polar optical phonons by introducing some effective relaxation time.

Performance evaluation of a new 30 μm thick GaAs x-ray detector grown by MBE

A circular mesa (400 μm diameter) GaAs p+-i-n+ photodiode with a 30 μm thick i layer was characterized for its performance as a detector in photon counting x-ray spectroscopy at 20 °C. The detector was fabricated from material grown by molecular beam epitaxy (MBE). An earlier MBE-grown detector fabricated using a different fabrication process and material from a different area of the same epiwafer was shown to suffer from: relatively high leakage current at high temperatures; a high effective carrier concentration that limited its depletion layer width; and material imperfections (butterfly defects) [Lioliou et al 2019 Nucl. Instrum. Methods Phys. Res. A 946 162670]. However, the new detector has better performance (lower leakage current and effective carrier concentration within the i layer). Using the new detector and low noise readout electronics, an energy resolution of 750 eV ± 20 eV Full Width at Half Maximum (FWHM) at 5.9 keV was achieved at 20 °C, equal to that reported for high quality GaAs detectors made from high quality material grown by metalorganic vapour phase epitaxy [Lioliou et al 2017 J. Appl. Phys. 122 244506]. The results highlight the substantially different performances of detectors made from the same epiwafer when the wafer qualities are not uniform and the effects of different fabrication processes.

Features of the electroresistivity, magnetic and galvanomagnetic characteristics in Co2MeSi Heusler alloys

The electro- and magneto-transport as well as magnetic properties of Co2MeSi (Me = Ti, V, Cr, Mn, Fe, Co, Ni) Heusler alloys were studied. The electroresistivity was measured from 4.2 to 300 K, the galvanomagnetic properties (magnetoresistivity and Hall effect) were measured at T = 4.2 K in magnetic fields of up to 100 kOe, and the magnetization at T = 4.2 and 300 K in fields of up to 70 kOe. The normal and anomalous Hall coefficients, saturation magnetization, residual resistivity, current carrier concentration, coefficients at linear contributions into the electroresistivity and magnetoresistivity were obtained. It was shown that on the one hand, there is quite clear correlation between the electronic and magnetic characteristics of Heusler alloys studied, and the spin polarization coefficients of current carriers, taken from well know literature data, on the other hand. The obtained results can be used for creation of new materials for spintronics.

Тензостимулированный эффект в легированном и термообработанном кремнии при ориентированной деформации

The tensostimulated effect in heat-treated and doped silicon was investigated. It is shown that uniaxial compression in the [111] direction leads to the decay of thermal donors and the hysteresis development in the dependences of the resistivity on the compression value. It was found that the strain-stimulated effect in manganese-compensated silicon samples is due to simultaneous changes in the concentration and mobility of current carriers.