Concentration Of Donor Impurities Research Articles

Optimization of the solar cell based on cadmium telluride by adding the CdSeTe absorbing layer (heterostructure simulation)

Cadmium telluride solar cells are among the most common devices for photovoltaic applications. However, the energy conversion efficiency of these elements remains insufficiently high. Using the SCAPS programming environment, research and optimization of a classical thin-film solar cell based on CdTe were carried out. The structure of this element consisted of ITO as a transparent conductive contact, a cadmium sulfide (CdS) layer, and a cadmium telluride (CdTe) absorber layer with a metal contact. To optimize this structure in terms of power conversion efficiency, the influence of the thickness and concentration of acceptor impurities in the CdTe absorbing layer, as well as the influence of the thickness and concentration of donor impurities in the CdS buffer layer, were considered. It was established that the optimal thicknesses for the CdS buffer layer and absorption CdTe layers are 50 nm and 3000 nm, respectively. An additional CdSeTe layer between the CdS and CdTe layers has been proposed as one of the optimization options to improve the device efficiency. The main photovoltaic parameters of such a solar cell were analyzed depending on the thickness of the CdSeTe layer and its selenium content. It has been demonstrated that adding CdSeTe solid solution to the 1500 nm thick CdTe absorber layer increases the efficiency of the solar cell by 6.84 %. The main photovoltaic characteristics of CdS/CdTe and CdS/CdSeTe/CdTe solar cells were compared. The results showed that the simulated CdS/CdSeTe/CdTe structure provides better photoconversion efficiency in the AM1.5G light spectrum compared to the classical CdS/CdTe structure. Such elements can be used to form highly efficient solar panels

CHANGES IN THE ELECTROPHYSICAL AND DETECTOR PROPERTIES OF THE PROMISING DETECTOR MATERIAL Cd1-xMnxTe DEPENDING ON THE CONCENTRATION OF IMPURITIES, DEFECTS AND MANGANESE CONTENT

A model study was carried out about the behavior of the resistivity ρ, the Fermi level F, and the charge collection efficiency η of detectors based on the promising semiconductor material Cd1-xMnxTe, depending on the donor impurity concentration ND for different values of the manganese molar fraction x: 0.035, 0.07, and 0.3 at room temperature. The values of concentrations Ni , activation energies Ei , and the capture cross sections σi of nonequilibrium charge carriers by i-th defects acted as input data for modeling. The regularities of changes in ρ, F, η depending on the content of impurities and cadmium vacancies have been established. Methods of achieving a highresistance state, proper for a material of detector-quality, are considered. A plan for further research issues using experimental published results is defined.

Correlating elemental compositions and charge carrier profiles in ultra-pure GaN/AlGaN stacks grown by molecular beam epitaxy

Inconsistencies in the concentrations of unintentional donor impurities and free charge carriers in GaN/AlGaN layer stacks hosting a two-dimensional electron gas (2DEG) can be attributed to the measurement procedure and solely depend on the way in which the free charge carrier concentration is extracted. Particularly, when the 2DEG acts as the bottom electrode in capacitance versus voltage measurements, unphysically low concentrations of free charges are calculated. This originates from the depletion of the 2DEG and the accompanying disappearance of the bottom electrode. It is shown that, for the case of a defined (non-vanishing) bottom electrode, the levels of donor impurities and resulting free charges consistently match.

Epitaxial n+-Ge/p+-Si(0 0 1) heterostructures with ultra sharp doping profiles for light emitting diode applications

The prototype light emitting diodes (LEDs) were fabricated from the n+-Ge/p+-Si(001) heterostructures grown by low-temperature Hot Wire Chemical Vapor Deposition. The n+-Ge epitaxial layers were heavily doped with P from a sublimation solid-phase GaP source. Abrupt profiles of the donor impurity concentrations at the n+-Ge/p+-Si heterojunctions were obtained. Negative differential resistance was observed in the current–voltage curves of the LEDs at forward bias. Electroluminescence (EL) related to the indirect (phonon-assisted) interband radiative optical transitions in the n+-Ge layers (from the l-valleys of the conduction band into the Г-point in the valence band) was observed at room temperature. The EL intensity increased with increasing P concentration in the n+-Ge layers.

Influence of impurities and structural defects on the properties of CdTe- and CdZnTe-based detectors

The most researched materials for uncooled semiconductor detectors of ionizing radiation are CdTe:Cl and Cd0.9Zn0.1Te, which allow to obtain detectors with high values of resistivity ρ and electron mobility. In the process of producing detector materials, the background impurities and defects can be introduced into their matrix, and as a result the deep levels appear in the bandgap, acting as centers of capture and recombination of nonequilibrium charge carriers and reducing the registration ability of detectors. The aim of this study was to determine by computer simulation method the nature of the effect of background impurities and structural defects on the electrophysical and detector properties of CdTe and CdZnTe. Quantitative studies were conducted using reliability-tested models. The authors used the examples of Cl, Fe, Pb, Cr, Co, Ti, V, Ni, Ge, Sn to study the effect of doping and background impurities on the resistivity ρ, lifetime of nonequilibrium electrons and holes, the charge collection efficiency η of detectors based on CdTe and Cd0.9Zn0.1Te. The influence of cadmium vacancies on the degradation of the ρ and η of the detectors based on the materials under study was clarified. Impurities were found that reduce ρ and η in detectors based on CdTe:Cl and Cd0.9Zn0.1Te:Al. The ultimate concentration of donor impurities and defects with their uniform distribution over the crystal volume without the formation of clusters was determined. The effect of the Fermi level and defect levels on the change and degradation of the properties of the materials under study was found. The ratios of the concentrations of background impurities and defects were established, making it possible to obtain semiconductors CdTe:Cl and Cd0.9Zn0.1Te of an acceptable detector quality.

Influence of the crystal substrate parameters on the maximum power of silicon heterojunction solar cells

The effect of the donor impurity concentration and the lifetime of charge carriers in a crystalline silicon substrate on the maximum power of heterojunction thin-film solar cells is studied. The model used in the calculations takes into account the features of photocurrent generation under conditions of medium or high levels of injection of charge carriers at an arbitrary ratio between the diffusion length and the thickness of the semiconductor wafer. The proposed technique makes it possible, with sufficient accuracy for practical purposes, to calculate the permissible variation limits of the substrate parameters, which ensure the specified values of the performance characteristics of photoelectric converters. Keywords: heterojunction solar cells, crystalline silicon substrates, optimal parameters, maximum power.

Influence of the crystal substrate parameters on the maximum power of silicon heterojunction solar cells

The effect of the donor impurity concentration and the lifetime of charge carriers in a crystalline silicon substrate on the maximum power of heterojunction thin-film solar cells is studied. The model used in the calculations takes into account the features of photocurrent generation under conditions of medium or high levels of injection of charge carriers at an arbitrary ratio between the diffusion length and the thickness of the semiconductor wafer. The proposed technique makes it possible, with sufficient accuracy for practical purposes, to calculate the permissible variation limits of the substrate parameters, which ensure the specified values of the performance characteristics of photoelectric converters. Keywords: heterojunction solar cells, crystalline silicon substrates, optimal parameters, maximum power.

Determination of the donor impurity concentration in thin i-InGaAs layers

This paper describes a technique that makes it possible, by analyzing the capacitance-voltage characteristics of metal-insulator-semiconductor or metal-semiconductor structures, to determine the concentration of the background donor impurity in undoped i-In0.53Ga0.47As layers with a thickness less than the width of the space charge region in the near-surface region of the semiconductor in strong inversion mode. Keywords: InGaAs, MIS structure, capacitance-voltage characteristic, dopant, space charge region.

Mass spectrometry as an effective method for measuring the concentration of donor impurities in bismuth films

Mass spectrometry as an effective method for measuring the concentration of donor impurities in bismuth films

Влияние параметров кристаллической подложки на максимальную мощность кремниевых гетеропереходных солнечных элементов

The effect of the donor impurity concentration and the lifetime of charge carriers in a crystalline silicon substrate on the maximum power of heterojunction thin-film solar cells is studied. The model used in the calculations takes into account the features of photocurrent generation under conditions of medium or high levels of injection of charge carriers at an arbitrary ratio between the diffusion length and the thickness of the semiconductor wafer. The proposed technique makes it possible, with sufficient accuracy for practical purposes, to calculate the permissible variation limits of the substrate parameters, which ensure the specified values of the performance characteristics of photoelectric converters.

Admittance of Barrier Structures Based on Mercury Cadmium Telluride

The results of studying the admittance of unipolar barrier structures based on HgCdTe grown by molecular beam epitaxy (MBE) on GaAs (013) substrates are presented. Using passivation with an Al2O3 insulator, device nBn structures based on HgCdTe were fabricated. The layer parameters in the created structures provided the possibility of detection in the spectral range of 3–5 μm. Based on the analysis of the frequency dependences of the admittance, an equivalent circuit of nBn structures at small biases is proposed. The dependences of the equivalent circuit parameters on the area of the mesa structure and temperature are determined. The properties of high-temperature maxima in the voltage dependences of the capacitance and conductance of nBn structures, which are presumably related to the recharging of surface states at the heterointerface between the barrier and absorbing layers, are studied. It is found that in a wide range of frequencies and temperatures, the capacitance – voltage characteristics of nBn structures based on HgCdTe at reverse biases can be used to determine the concentration of donor impurities in the absorbing layer. It is shown that the admittance of test MIS devices in a mesa configuration, formed on the basis of the MBE HgCdTe nBn structures, is determined by the combined influence of electronic processes in the contact, barrier, and absorbing layers.

Charge stability of nitrogen-vacancy color centers in organic nanodiamonds

The negatively-charged nitrogen-vacancy (NV) color center in diamond undergoes stochastic charge state transitions between the negatively charged state (NV−) and the neutral charged state (NV o ) upon optical illumination. While the negative charge state is normally preferred for magnetic sensing, optically-controlled switching between charges states is often desirable, for example in super-resolution imaging. The concentration of electron donor impurities in (bulk/nano) diamond crystals determine how much optical control can be exercised over the NV− and NV o charge states. Here we report how the growth speed of nanodiamonds (NDs) can control the concentration of substitutional nitrogen (P1) donors, ranging from highly pure to highly doped diamond. Hence by growth temperature, it is possible to tune the stability of the NV charge state to optimally match the intended application. This work has many promising bio-sensing applications, especially for super-resolution magnetic-sensing with the NV color center.

The physics-based model of AlGaN/GaN high electron mobility transistor outer fringing capacitances

<sec> With the development of the application of AlGaN/GaN high electron mobility transistors in the radio frequency field, a capacitance model that can accurately describe the <i>C</i>-<i>V</i> characteristics of the device has become an important research topic. The gate capacitance of GaN HEMT can be divided into two parts: intrinsic capacitance and fringing capacitance related to two-dimensional electronic gas (2DEG) electrode. The fringing capacitance plays an important part in the switching device. The outer fringing capacitance <i>C</i><sub>ofs/d</sub> dominates the fringing capacitance and is affected by the bias applied, especially the drain outer fringing capacitance <i>C</i><sub>ofd</sub>.</sec><sec> In order to establish the <i>C</i><sub>ofd</sub> model which is related to the bias condition, the physics-based model of <i>C</i><sub>ofd</sub> is established based on the conformal mapping, including the drain channel length variable. Since the drain channel length is related to the bias applied, the channel length modulation effect can be used to study how bias apllied effect the channel, and the relationship between <i>C</i><sub>ofd</sub> and the bias condition is obtained. In addition, the threshold voltage variable is introduced when the channel length modulation effect is considered, and the threshold voltage drift caused by changes in the internal parameters and temperature of the device is studied using the threshold voltage variable in the model, and the relationship between <i>C</i><sub>ofd</sub> and threshold voltage and temperature under different bias was obtained.</sec><sec> It is found from the results of the study that as drain bias increases from zero, the channel length modulation effect keeps <i>C</i><sub>ofd</sub> unchanged at lower drain bias. When the drain bias continues to increase, <i>C</i><sub>ofd</sub> begins to decay again, and its decay rate slows down with the increase of gate bias. The decrease of donor impurity concentration and Al component in AlGaN barrier layer may increase the threshold voltage, which will strengthen the channel length modulation effect on <i>C</i><sub>ofd</sub>, resulting in linear attenuation of <i>C</i><sub>ofd</sub>. With the increasing of drain bias, the influence of threshold voltage shift on <i>C</i><sub>ofd</sub> is enhanced, and the change of device operating temperature will enhance the threshold voltage shift and cause the deviation of <i>C</i><sub>ofd</sub>. Moreover, with the continuous increase of drain bias, <i>C</i><sub>ofd</sub> becomes more sensitive to the temperature variation.</sec>

Concentration dependences of electrical conductivity and the Hall effect of the CexSn1–xSe single crystals

The concentration dependences of the Hall coefficient, electrical conductivity, and charge carrier mobility in CexSn1–xSe (х ≤ 0.02) are studied over a temperature range of 77–400 K. In the considered samples, impurities are compensated with intrinsic defects. As the cerium concentration increases (x = 0.01; 0.015), the concentration of donor impurities grows, and a change in the type of conductivity is observed.

Miniband Electrical Conductivity in Superlattices of Spherical InAs/GaAs Quantum Dots

The electrical properties of nanoscale semiconductor InAs/GaAs heterosystems with 2D-superlattices of spherical quantum dots have been studied. The dependences of the electron group velocity on the wave vector and the miniband quantum number are obtained. The dependences of the Fermi level of electrons in minibands on the concentration of donor impurities, donor energy, and temperature are found. The temperature dependences of the majority carrier concentration and the electrical conductivity are analyzed for various donor concentrations and energies.

Investigation of the Far-IR Reflection Spectra of SmS Single Crystals and Polycrystals in the Homogeneity Range

The far- and mid-IR reflection spectra of Sm1 + x S (x = 0–0.17) samples are recorded and analyzed, as well as their electrical and structural parameters at a temperature of T = 300 K. The bond ionicity in SmS is shown to fall with a decrease in the area of the X-ray coherent scattering region and an increase in the concentration of donor impurities and, consequently, conduction electron concentration. The electrical conductivity of stoichiometric SmS single crystals and polycrystals can be determined with an error of 10% from the IR reflection spectra. Due to the low structural quality of the samples, the electrical conductivity cannot be determined in the case of deviation from stoichiometry.

Исследование длинноволновых инфракрасных спектров отражения моно- и поликристаллов SmS в области гомогенности

AbstractThe far- and mid-IR reflection spectra of Sm_1 + x S ( x = 0–0.17) samples are recorded and analyzed, as well as their electrical and structural parameters at a temperature of T = 300 K. The bond ionicity in SmS is shown to fall with a decrease in the area of the X-ray coherent scattering region and an increase in the concentration of donor impurities and, consequently, conduction electron concentration. The electrical conductivity of stoichiometric SmS single crystals and polycrystals can be determined with an error of 10% from the IR reflection spectra. Due to the low structural quality of the samples, the electrical conductivity cannot be determined in the case of deviation from stoichiometry.

A study of the effect of electron and proton irradiation on 4H-SiC device structures

The changes of the current–voltage characteristics and the uncompensated donor-impurity concentration (N d –N a ) in the base electrode of Schottky diodes and JBS diodes based on 4H-SiC have been studied upon their irradiation with 0.9-MeV electrons and 15-MeV protons. The carrier-removal rate was 0.07–0.15 cm–1 under electron irradiation and 50–70 cm–1 under proton irradiation. It was shown that the current–voltage characteristics of the devices under study remain rectifying at electron irradiation doses of up to ~1017 cm–2. It was demonstrated that the radiation hardness of the SiC-based devices under study substantially exceeds that of silicon p–i–n diodes with similar breakdown voltages.

Simulation Comparison of Self-Heating Effects in Junctionless Nanowire Transistors and FinFET Devices

I. Introduction In order to reduce the short channel effects, junctionless nanowire transistors (JNT) can be a very interesting option once it avoids the lateral diffusion of impurities from source and drain regions to the channel. In addition, as they are a multiple gate devices it is possible to improve the electrostatic control over the channel charges [1-4]. While the channel in state-of-art nFinFET devices is undoped or lightly doped with p-type impurities, n-type JNT have a uniform heavy concentration of donor impurities from source to drain, which simplifies the device fabrication, once it dispenses complicated annealing techniques [5-6]. A schematic view and a longitudinal-section of n-type JNT and FinFET devices are shown on Fig. 1. As demonstrated in Fig. 1 JNT and FinFET are made using Silicon-On-Insulator (SOI) substrates. The thermal resistance associated to the buried oxide is in order of 100 times larger than silicon. Thus, both device alternatives can suffer from the difficulty of dissipating the heating of the silicon film caused by the Joule effect thanks to the current conduction, the so-called self-heating effect (SHE). This paper aims at comparing the self-heating effects (SHE) between FinFET and JNT devices using three-dimensional simulation. II. Devices Characteristics The comparison of SHE between JNT and FinFET devices by means of three-dimensional numerical simulations has been performed with Synopsys Sentaurus Device simulator [10]. Both JNT and FinFET devices have been simulated with gate oxide thickness of 2nm, channel length (L) of 0.5 µm and 1 µm, fin width (Wfin ) of 10 nm and 20nm, fin height (Hfin ) of 60 nm and 10nm. For the JNT P+ polysilicon was used as gate material. The JNT has been doped uniformly with 5x1018 cm-3 and 1x1019 cm-3 with n-type impurities, while the channel region of FinFET has been doped with 1x1015 cm-3with p-type impurities. In order to avoid the series resistance, the drain and source extensions were simulated with 5nm. The buried oxide thickness is 100 nm. The simulations have been done with isothermal grid at 300K where there is no self-heating effect (hereafter mentioned as without SHE) as well as with thermal contact at the buried oxide allowing the thermal generation to be accounted in the several grid points (hereafter mentioned as with SHE). III. Results and analysis Fig.2 and Fig. 3 present the behavior of the drain current as a function of gate voltage for FinFET and JNT. It is possible to compare the simulations with and without SHE, which present the same behavior i.e., there is no clear SHE due to the lower VD (50mV) resulting in lower static power (P = VD.ID ). According to the results obtained for lower VD, it is possible to confirm that those simulations are calibrated for analysis with higher VD values since their behavior are the same, independently if accounting or not the silicon film heating. On the other hand, when the VD increased to 1.5V, it is clearly visible the presence of the SHE in both JNT and FinFET as the current with non-isothermal grid is smaller than with isothermal one, thanks to the mobility degradation due to temperature rise. Finally, Fig. 4 shows the curves for the difference between drain current without SHE and with SHE (ΔID ), for the same VGT as a function of the power with SHE. The results show that, for the same power level, the ΔID is higher in FinFET devices i.e, the self-heating effect degrades the drain current much more than compared in JNT. Conclusions According to the results simulated, JNT suffer less self-heating effect when compared with a similar FinFET devices due to the decreasing of the mobility variation with temperature. acknoledgment The authors acknowledge CAPES, FAPESP and CNPq for the financial support. References D. Hisamoto et al., IEEE Transactions on Electron Devices, vol.47 , pp. 2320-2325, 2000. J. T. Park et al., IEEE Electron Device Letters, vol.22, pp. 405-406, 2001. J. P. Colinge et al., IEEE Electron Device Letters, vol.24, pp. 515-517, 2003. J. P. Colinge et al., Proceeding of IEEE International SOI Conference, pp. 1, 2009. C. W. Lee et al., Appl. Phys. Lett., vol. 94, no. 5, p. 053 511, Feb. 2009. J. P. Colinge et al., Nat. Nanotechnol., vol. 5, no. 3, pp. 225–229, Mar. 2010. G. Mariniello et al., Symposium on Microelectronics Technology and Devices (SBMICRO) 2013 v.1 p1-4. A. Kranti et al., Solid-State Electronics, vol. 65-66, pp. 33-37, Dec. 2011. S. Zimin et al., Proc. ICSICT, 1998, pp. 572-574. Sentaurus Device User’s Manual, Synopsys, 2013. Figure 1

Hydride vapor phase GaN films with reduced density of residual electrons and deep traps

Electrical properties and deep electron and hole traps spectra are compared for undoped n-GaN films grown by hydride vapor phase epitaxy (HVPE) in the regular process (standard HVPE samples) and in HVPE process optimized for decreasing the concentration of residual donor impurities (improved HVPE samples). It is shown that the residual donor density can be reduced by optimization from ∼1017 cm−3 to (2–5) × 1014 cm−3. The density of deep hole traps and deep electron traps decreases with decreased donor density, so that the concentration of deep hole traps in the improved samples is reduced to ∼5 × 1013 cm−3 versus 2.9 × 1016 cm−3 in the standard samples, with a similar decrease in the electron traps concentration.