Current Carrier Concentration Research Articles

Analysis of Defect‐Free Graphene Blocks in Nitrogen‐Doped Bamboo‐Like Carbon Nanotubes

The structure and electronic properties of the N‐doped bamboo‐like carbon nanotubes with different nitrogen content (N‐CNTs) are studied by the use of transmission electron microscopy, electron energy loss spectroscopy, Raman spectroscopy, and X‐ray photoelectron spectroscopy supplemented by measurements of the temperature dependence of conductivity. XPS data are used to estimate the content of nitrogen represented by pyridinic, pyrrolic, graphitic, and oxidized N species and encapsulated molecular nitrogen. The graphene blocks surrounded by borders containing hole defects and N‐species are considered as building blocks of N‐CNT walls. The intensity ratio of D, G, and 2D bands in Raman spectra and XPS data on the concentration of N‐species are used to analyze the size of defect‐free graphene blocks in N‐CNTs. The size of such blocks depends on the N‐defect content and is estimated to be 1–2 nm. The increase of N‐species content resulting in a decrease of graphene block size correlates with the decrease of current carrier concentration (nES) estimated within the Efros–Shklovskii model.

Electrical conductivity in single crystals of GaSe x Te1 – x solid solutions in strong electrical fields

This paper presents some results of studying the Poole–Frenkel effect with allowance for shielding in layered GaSe and GaTe single crystals and their solid solutions in strong electrical fields of up to 105 V/cm at temperatures of 103–250 K. According to the relationship \(\left(\frac{\sigma}{\sigma(0)}\right)^{1/2}\) log\(\frac{\sigma}{\sigma(0)} = E\sqrt{\frac{\varepsilon}{4\pi n(0)kT}}\), there exists a linear dependence between \(\left(\frac{\sigma}{\sigma(0)}\right)^{1/2}\) log\(\frac{\sigma}{\sigma(0)}\) and the electrical field E (σ is the electrical conductivity in strong electrical fields, and σ(0) is the electrical conductivity in the ohmic region). The slopes of these lines have been determined at different temperatures (103–250 K) by estimating the concentration of current carriers n(0) = 3 × 1013–5 × 1015 cm–3 in the ohmic region of the electrical conductivity of solid solutions of layered GaSe x Te1–x single crystals (x = 1.00, 0.95, 0.90, 0.80, 0.70, 0.30, 0.20, 0.10, 0).

Investigation of X-ray diffraction limitations upon the analysis of tellurium-atom injection into GaAs epitaxial layers

GaAs lattice “superdilation” caused by an introduced tellurium impurity, which is well known in publications, is experimentally studied. This phenomenon consists in the fact that the GaAs-lattice dilation can be more than 10 times greater than expansion that would appear upon the replacement of arsenic atoms with tellurium atoms if calculations are performed using the current-carrier concentration and Vegard’s law. The given phenomenon has already been observed at n Te > 3 × 1018 cm–3. A series of GaAs epitaxial layers heavily doped with tellurium and grown via metal-organic chemical vapor deposition are investigated using high-resolution X-ray diffractometry (HRXRD), secondary-ion mass spectrometry (SIMS), and the Hall effect. It is demonstrated that, despite a high Te concentration (1020‒1021 cm–3) in the layer and variations in the growth conditions, the concentration estimates based on HRXRD data depend linearly on the results of elemental analysis performed by means of SIMS. The GaAs lattice expands even somewhat slighter as compared to the case where arsenic atoms are replaced with all Te atoms injected into the layer. At the same time, the Hall carrier concentration decreases sharply beginning at 2 × 1020 cm–3. In accordance with the obtained results, the examined phenomenon can be interpreted as the strong compensation of donor and acceptor carriers rather than as superdilation.

STUDIES ON EFFECTIVE SEGREGATION COEFFICIENTS OF IMPURITIES IN SILICON PULLED FROM MG-Si MELT

Minimization of impurities content in Si necessary for its application as semiconductor material is performed by using directional crystallization of metallurgical grade Si ( n -MG-Si) with 98 wt. % Si purity without intermediate stages. After pulling from melt, n -MG-Si goes into p- type Si with current carriers concentration ( p ) ~ 10 16 cm –3 and Si has been purified practically from majority of impurities. The possibility of uncontrolled impurities removal from Si depends on impurities effective coefficient of segregation in Si. Therefore we have investigated the effective coefficient of segregation of unwanted impurities in Si crystals, obtained by pulling directly from MG-Si melt. In the presented article the effective segregation coefficient of major impurities in Si has been calculated and analysed in the dependence on the crystallization conditions. Effective coefficient of segregation makes possible estimate the capacity and efficiency of Si purification from impurities during crystallization from melt.

Performance Analysis of GaN-Based Light-Emitting Diodes With Lattice-Matched InGaN/AlInN/InGaN Quantum-Well Barriers

In this paper, the properties of GaN-based light-emitting diodes (LEDs) with lattice-matched InGaN/AlInN/InGaN (LM-IAI) quantum-well (QW) barriers are investigated numerically. Distributions of electrostatic field, carrier current density, carrier concentration and radiative recombination rate are simulated, and internal quantum efficiency (IQE) and emission power are calculated. The results show that the LEDs with LM-IAI barriers have higher IQE and emission power over their conventional counterparts with GaN barriers due to the mitigation of the quantum-confined Stark effect and the suppression of electron leakage. Furthermore, the performances of the nitride-based LEDs with the proposed barriers can be further improved by dismissing the electron-blocking layer, which is attributed to the improvement of hole injection efficiency and the decrease of overall Auger recombination.

Possibilities of applying plasma technologies for processing organics-containing substances: The effect of the shape of the voltage curve on the working mode of the plasma torch

The features of alternating current plasma torches with rod electrodes and the phenomena and regularities observed during their work in a wide power range of 0.1–7 MW are considered. The mechanism of the reignition of the arc in the single-phase and three-phase working modes of a plasma torch is studied. The characteristic differences of these processes, the existence of which is explained by the conservation of the concentration of current carriers in the interelectrode gap in the three-phase mode, are given. It is shown that the reignition voltage varies in accordance with the variation of the temperature of the electrode surface, and the electrode temperature saturated with the increase in the current and the reignition voltage is constant. Particular attention is paid to analysis of the external characteristics of plasma torches in different working modes when using nitrogen, hydrogen, or argon as the working gas. The effect of the physical parameters of plasma on the shape of the voltage curves and current–voltage characteristic of arcs is considered, and the dependence of the energy parameters of plasma torches on them is described.

Crystal-Quasichemical Analysis of Defect Subsystem of Doped PbTe: Sb Crystals and Pb-Sb-Te Solid Solutions

Within crystalquasichemical formalism models of point defects of crystals in the Pb-Sb-Te system were specified. Based on proposed crystalquasichemical formulae of antimony doped crystals PbTe:Sb amphoteric dopant effect was explained. Mechanisms of solid solution formation for РbТе-Sb2Те3: replacement of antimony ions lead sites with the formation of cation vacancies (I) or neutral interstitial tellurium atoms (II) were examined. Dominant point defects in doped crystals PbTe:Sb and РbТе-Sb2Те3 solid solutions based on p-PbTe were defined. Dependences of concentration of dominant point defects, current carriers and Hall concentration on content of dopant compound and the initial deviation from stoichiometry in the basic matrix were calculated.

Wurtzite Cu2ZnSnS4 nanospindles with enhanced optical and electrical properties

Wurtzite CZTS nanospindles were prepared through facile one-pot method. XRD, TEM and SEM characterizations confirm the structure and morphology of the as-obtained CZTS nanospindles. The CZTS nanospindles show obviously enhanced optical and electrical properties. The CZTS nanospindles can harvest incident lights more efficiently (light-trapping effect), which can significantly improve the photovoltaic properties of the CZTS films. Under same condition, the photocurrent gain in nanospindles film is larger than that of nanorices film. These results indicate that CZTS nanospindles are favorable to increase current carrier concentration and improve electron transmission, which may improve performance of photovoltaic devices in the future.

Study of transport properties of copper/zinc-oxide-nanorods-based Schottky diode fabricated on textile fabric

In this work, a copper/zinc-oxide (ZnO)-nanorods-based Schottky diode was fabricated on the textile fabric substrate. ZnO nanorods were grown on a silver-coated textile fabric substrate by using the hydrothermal route. Scanning electron microscopy and x-ray diffraction techniques were used for the structural study. The electrical characterization of copper/ZnO-nanorods-based Schottky diodes was investigated by using a semiconductor parameter analyzer and an impedance spectrometer. The current density–voltage (J–V) and capacitance–voltage (C–V) measurements were used to estimate the electrical parameters. The threshold voltage (Vth), ideality factor (η), barrier height (ϕb), reverse saturation current density (Js), carrier concentration (ND) and built-in potential (Vbi) were determined by using experimental data and (simulated) curve fitting. This study describes the possible fabrication of electronic and optoelectronic devices on textile fabric substrate with an acceptable performance.

New Opportunities in Lead Selenide Nanolayers

The article deals with the peculiarities of creation of effective negative pressure and the increase in the forbidden gap width in PbSe nanolayers. The dielectric state that maybe realized under these conditions and their appropriate doping can be considered as a new resource in lead selenide nanolayers. The increasing of the tangential lattice constant with higher growth temperature and layer growth rate confirms this consideration. When determining the forbidden gap width, the optical transmission spectra were processed by a model of the Fabry-Perot interferometer, and, at high concentration of free current carriers, the absorption on them and their degeneracy were taken into consideration.

Impact of proton irradiation on dc performance of AlGaN/GaN high electron mobility transistors

The effects of high energy proton irradiation dose on dc performance as well as critical voltage of the drain-voltage step-stress of AlGaN/GaN high electron mobility transistors (HEMTs) were investigated to evaluate the feasibility of AlGaN/GaN HEMTs for space applications, which need to stand a variety of irradiations. The HEMTs were irradiated with protons at a fixed energy of 5 MeV and doses ranging from 109 to 2 × 1014 cm−2. For the dc characteristics, there was only minimal degradation of saturation drain current (IDSS), transconductance (gm), electron mobility, and sheet carrier concentration at doses below 2 × 1013 cm−2, while the reduction of these parameters were 15%, 9%, 41% and 16.6%, respectively, at a dose of 2 × 1014 cm−2. At this same dose condition, increases of 37% in drain breakdown voltage (VBR) and of 45% in critical voltage (Vcri) were observed. The improvements of drain breakdown voltage and critical voltage were attributed to the modification of the depletion region due to the introduction of a higher density of defects after irradiation at a higher dose.

Current–voltage characteristic of a p-Ge/n-GaAs heterostructure with oncoming heat fluxes

The work is aimed at search for methods of increasing the rectification coefficient of devices based on heterostructures (HS). The current-voltage characteristics (CVC) of hetero semiconductors (HSC) with oncoming heat fluxes and large temperature gradient (LTG) are investigated. It is well known that the LTG is understood as a temperature gradient at which the concentration of minority current carriers changes already on the diffusion length [1].

Crystalquasichemical model of point defects in mercury telluride

One of the most important problems of chemistry of solids and chemical engineering are the analysis of point defects influence on the properties of semiconductors and directed control of their modes and concentration. A great number of monographs, reviews and international conferences are devoted to this subject area. As to HgTe, while studying damage processes, quasichemical models with various combinations of point defects appeared to be the most effective. Alongside, the involvement of the new crystalquasichemical method to the analysis of defective subsystem of stoichiometric as well as non-stoichiometric crystals makes it possible to examine the actual nature of point defects. This is the foundation for the research of solid solution mechanism. The crystalquasichemical method concerning the research of defective subsystem of HgTe was used in the paper. It gives an opportunity to analyze crystalchemical compatibility or incompatibility of defects formation and to calculate the concentration of point defects and current carriers, taking into consideration the deflection from stoichiometry and the part of ionic bond of atoms in crystals. It was determined that within the limits of homogeneity the vacancies V 2+ Te and interstitial mercury atom Hg 2+ i dominating in n-HgTe for the n-type material, and the mercury vacancies V - Hg , V 2- Hg for the p-type material.Changing HgTe crystal structure (within the limits of homogenity) it is possible to control their properties, in particular value of band gap, electrical, optical and magnetic characteristic.

Recombination via tail states in polythiophene:fullerene solar cells

State-of-the-art models used for drift-diffusion simulations of organic bulk heterojunction solar cells based on band transport are not capable of reproducing the voltage dependence of dark current density and carrier concentration of such devices, as determined by current-voltage and charge-extraction measurements. Here, we show how to correctly reproduce this experimental data by including an exponential tail of localized states into the density of states for both electrons and holes, and allowing recombination to occur between free charge carriers and charge carriers trapped in these states. When this recombination via tail states is included, the dependence of charge-carrier concentration on voltage is distinctly different from the case of band-to-band recombination and the dependence of recombination current on carrier concentration to a power higher than 2 can be explained.

Non-Gaussian conductivity fluctuations in semiconductors

A theoretical study is presented on the statistical properties of conductivity fluctuations caused by concentration and mobility fluctuations of the current carriers. It is established that mobility fluctuations result from random deviations in the thermal equilibrium distribution of the carriers. It is shown that mobility fluctuations have generation–recombination and shot components which do not satisfy the requirements of the central limit theorem, in contrast to the current carrier's concentration fluctuation and intraband component of the mobility fluctuation. It is shown that in general the mobility fluctuation consist of thermal (or intraband) Gaussian and non-thermal (or generation–recombination, shot, etc.) non-Gaussian components. The analyses of theoretical results and experimental data from literature show that the statistical properties of mobility fluctuation and of 1/ f-noise fully coincide. The deviation from Gaussian statistics of the mobility or 1/ f fluctuations goes hand in hand with the magnitude of non-thermal noise (generation–recombination, shot, burst, pulse noises, etc.).

Specific features of electron autoemission from some low-dimensional systems in a quantizing magnetic field

The possibility of the appearance of kinks (including multiple ones) on curves of the dependence of the autoelectron current on the transverse-quantizing-magnetic-field strength for low-dimensional systems containing a film or superlattice is indicated. It is shown that these specific features are related to jumps of the Fermi level and, therefore, the jumps of the film or superlattice work function and allow determination of the concentration of current carriers in studied objects.

Analysis of the leakage current in GaN-based heterostructure buffer layer

The relations between the buffer leakage current and the characteristics of nucleation layer of AlGaN/GaN heterostructure have been obtained by comparative study of depletion capacitance of C-V characteristics in GaN-based heterostructure. The results showed that, the heterostructure material based on a sapphire substrate with a low-temperature GaN nucleation layer and SiC substrate with a high-temperature AlN nucleation layer have smaller buffer leakage current and lower carrier concentration of the background GaN buffer layer than that based on a sapphire substrate with a low-temperature AlN nucleation layer. A thorough analysis shows that, there is an n-type GaN conductive layer near the GaN/substrate interface in buffer layer based on the thinner nucleation layers. Contrarily, high resistivity GaN buffer layers appear in heterostructure materials based on thicker nucleation layer. One of the main causes of device leakage is the n-type GaN conductive layer. Appropriately improving the quality and thickness of nucleation layer can effectively reduce the carrier concentration, raise the resistivity and suppress the leakage current of the GaN buffer layer.

Fractal properties of nanostructured semiconductors

A theory for the temperature and time dependence of current carrier concentration in semiconductors with different non-equilibrium nanocluster structure has been developed. It was shown that the scale-invariant fractal self-similar and self-affine laws can exist near by the transition point to the equilibrium state. Results of the theory have been compared to the experimental data from electrical properties of semiconductor films with nanoclusters.

The role of primary point defects in the degradation of silicon detectors due to hadron and lepton irradiation**Work in the frame of CERN-RD50 Collaboration.

The principal obstacle to long-time operation of silicon detectors at the highest energies in the next generation of experiments arises from bulk displacement damage which causes significant degradation of their macroscopic properties. The analysis of the behaviour of silicon detectors after irradiation conduces to a good or reasonable agreement between theoretical calculations and experimental data for the time evolution of the leakage current and effective carrier concentration after lepton and gamma irradiation and large discrepancies after hadron irradiation and this in conditions where a reasonable agreement is obtained between experimental and calculated concentrations of complex defects. In this paper, we argue that the main discrepancies could be solved naturally considering as primary defects the self-interstitials, classical vacancies and the new predicted fourfold coordinated silicon pseudo-vacancy defects. This new defect is supposed to be introduced uniformly in the bulk during irradiation, has deep energy level(s) in the gap and it is stable in time. Considering the mechanisms of production of defects and their kinetics, it was possible to determine indirectly the characteristics of the SiFFCD defect: energy level in the band gap and cross-section for minority carrier capture. In the frame of the model, the effects of primary defects on the degradation of silicon detectors are important in conditions of continuous long-time irradiation and/or high fluences.

Concentration Effects on n-GaN Schottky Diode Current-Voltage (i-v) Characteristics

We focus on the epi layer carrier concentration variation effects to improve the current – voltage (I-V) characteristics of an n-GaN schottky diode. The carrier concentration of 1×10 15cm-3, 1×1016 cm−3, 1×1017 cm−3 were employed. The simulated current was obtained by forward biasing the device of up to 2Volt at room temperature using Pt electrode. The study was conducted by using Atlas/Blaze using various models such as Consrh (Concentration Dependent Shockley Read Hall), Cvt (Lombardi Model), Fermi (Fermi Dirac), Bgn (Bandgap Narrowing), Conmob (Concentration Dependent Mobility), Auger (Auger). We found that as the concentration increases the value of forward current also increase linearly when biased at maximum of 2 volts. The reverse bias characteristics at the same concentration of the simulated diode up to 100Volt were also determined. We found that at low carrier concentration the reverse leakage current is minimum and breakdown voltage is maximum. As the carrier concentration increases there is a linear relationship between reverse leakage current and epi layer doping carrier concentration. By analyzing the forward and reverse characteristics we conclude that in forward bias for low carrier concentration the diode shows schottky rectifying behavior while for higher carrier concentration the diode shows ohmic behavior. For higher carrier concentration there is a linear relationship between carrier concentration (n) and forward current. The reverse leakage current is minimum approaching an ideal value at n≤1×1015cm-3 and breakdown voltage is maximum at these values of concentration. Increasing the concentration from n≤1×1015cm-3 the value of reverse leakage current is approaching to the maximum value as a result breakdown voltage decreases. We conclude that for n-GaN schottky diode the ideal schottky rectifying behavior of I-V characteristics is obtained at carrier concentration of n≤ 1×1015cm-3 for the simulated diodes at different carrier concentration.