Acceptor Impurities Research Articles

Cultural characteristics Meyerozyma guilliermondii TY-89 on lard

We have investigated the effect of co-doping of nitrogen (N) acceptor impurity on the structural and magnetic properties of (Zn,Fe)Te. We grew (Zn,Fe)Te:N thin films by molecular beam epitaxy (MBE) with a fixed Fe composition 1.5% and varied N concentrations in the range of [N] = 8 × 1017– 4 × 1019 cm−3. Structural analyses by using x-ray absorption fine structure (XAFS) and transmission electron microscope (TEM) reveal that N-doped films with intermediate N concentration [N] = 8 × 1017– 7 × 1018 cm−3 are mainly composed of pure diluted phase with substitutional Fe atoms in the valence state deviated from Fe2+, while Fe is dominantly incorporated in an Fe-N compound at the highest N concentration [N] = 4 × 1019 cm−3. Accordingly, the magnetization measurement using SQUID confirms a drastic change of magnetic properties; a linear dependence of magnetization of magnetic field (M-H), typical of van-Vleck paramagnetism in the film without N-doping changes into ferromagnetic behaviors with a hysteretic M-H curves at the intermediate N concentrations and comes back to a linear M-H dependence at the highest N concentration. The ferromagnetism in the intermediate [N] range may reflect a deviation of the valence state of the substitutional Fe from Fe2+, while the linear M-H at the highest [N] would be attributed to precipitates of an Fe-N compound.

Gd and Tb doping effects on the physical properties of Nd2Sn2O7

In the current study, we report the light doping effects of the gadolinium and the terbium on the structural, morphological, optical and electrical properties of Nd2Sn2O7 pyrochlore ceramics. The pyrochlore which is prepared by the conventional solid state reaction technique is analyzed by means of scanning electron microscopy, energy dispersive X-ray analyzer, X-ray diffraction, ultraviolet- visible light spectrophotometry and temperature dependent current -voltage characteristics techniques. It is found that even though the doping content of both metals is low (2%), they significantly alter the physical properties of the pyrochlore. Particularly, it is observed that, these two doping agents increases the lattice parameter and strain and reduces the crystallite size and dislocation density. Optically, the effect of Gd doping on shrinking the energy band gap value of the Nd2Sn2O7 pyrochlore ceramic is more pronounced than that of Tb. On the other hand, the electrical investigations have shown that while the Gd make the pyrochlore exhibit p–type conductivity through forming shallow acceptor levels, the Tb forces n-type conductivity by forming deep donor levels below the conduction band edge. Such acceptor and donor impurity levels increases the electrical conductivity of the Nd2Sn2O7 pyrochlore ceramics by 390 and 58 times, respectively.

Optimizing two and four-terminal CuGaSe2/CuInGaSe2 tandem solar cells for achieving high efficiencies

Solar cells based on CuInGaSe2 (CIGS) have attained the highest record efficiency (22.9%) among thin film solar cells. CIGS is formed by the appropriate mixing of CuInSe2 (CIS) which has a bandgap around 1 eV and CuGaSe2 (CGS) which has a bandgap around 1.7 eV. These bandgaps are close to the optimal values for two-junction tandem solar cells. Therefore, CGS on CIGS or CGS on CIS tandem cells should be attractive and viable to achieve high efficiency and cost-effective thin film solar cells. In this work, a simple unified analytical model is used to design two-terminal and four-terminal CGS/CIGS tandem solar cells, establishing a realistic value for the expected efficiency in each case. Short circuit current density (Jsc), open circuit voltage (Voc), fill factor (FF) and efficiency, are determined as a function of the CGS and CIGS acceptor impurity concentrations, back surface recombination velocities, minority carrier diffusion lengths, and absorber layer thickness. It is shown that realistic efficiencies over 30% can be achieved under one sun AM1.5 spectrum for both of the terminal configurations, but the optimum composition for the CIGS sub-cell should be different depending on the respective tandem cell configuration.

Atomistic tight-binding theory for acceptor states (C, Be, Mg, Zn, Si and Cd) of GaAs nanocrystals

The atomistic tight-binding theory is introduced as a new way to numerically calculate the binding energies of acceptors (C, Be, Mg, Zn, Si and Cd) in GaAs nanocrystals. In the present paper, the electronic structures and optical properties of spherical GaAs nanocrystals with a single substitutional acceptor impurity at the center and off-center sites are studied. The optical band gaps of undoped GaAs nanocrystals are larger for smaller nanocrystals, due to quantum confinement effects. Numerical results show that the acceptor binding energies are highly dependent on the nanoparticle sizes, impurity types and positions. Larger acceptor binding energies in doped GaAs nanocrystals are also seen for smaller nanocrystals. In term of acceptor varieties, the high-to-low order of binding energies is found in Cd, Si, Zn, Mg, Be and C acceptors, respectively. In term of positions, the acceptor binding energies are reduced with the increasing distances from the center of nanocrystals. In addition, the optical property is mainly improved in the presence of the substitutional acceptor impurity. Finally, these computational results provide an inroad to new materials not accessible via other means with the aim to implement novel applications based on the substitutional acceptor impurity in the nanostructures.

Concentration Dependences of the Thermoelectric Parameters of Pb1–xAgxS and Pb1–xCuxS (0 ≤ x ≤ 0.011) Solid Solutions

The concentration dependences of Seebeck coefficient S, resistivity ρ, thermal conductivity κtot, and Hall constant RH are studied for mixed Pb1–xAgxS and Pb1–xCuxS crystals in the 0 < x ≤ 0.011 range of concentrations at T = 300 K. It is found that silver is an acceptor impurity and can induce conductivity inversion (from n-type to p-type) in Pb1 − xAgxS samples at x ≈ 0.0045. Such inversion is not observed in the S(х), ρ(х), κtot(x), and RH(x) dependences for Pb1–xCuxS (0 < x ≤ 0.011), though the acceptor behavior of the copper impurity was also apparent in these dependences.

A survey of acceptor dopants for β-Ga2O3

With a wide band gap, high critical breakdown voltage and commercially available substrates, Ga2O3 is a promising material for next-generation power electronics. Like most wide-band-gap semiconductors, obtaining better control over its electrical conductivity is critically important, but has proven difficult to achieve. Although efficient p-type doping in Ga2O3 is not expected, since theory and experiment indicate the self-trapping of holes, the full development of this material will require a better understanding of acceptor dopants. Here the properties of group 2, group 5 and group 12 acceptor impurities in β-Ga2O3 are explored using hybrid density functional calculations. All impurities are found to exhibit acceptor transition levels above 1.3 eV. After examining formation energies as a function of chemical potential, Mg (followed closely by Be) is determined to be the most stable acceptor species.

Mechanism of the Generation of Donor–Acceptor Pairs in Heavily Doped n-ZrNiSn with the Ga Acceptor Impurity

The nature of the mechanism of the simultaneous generation of donor–acceptor pairs under heavy doping of n-ZrNiSn intermetallic semiconductor with the Ga acceptor impurity is established. Such spatial arrangement in the crystal lattice of ZrNiSn1–xGa x is found when the rate of movement of the Fermi level eF found from calculations of the density distribution of electron states coincides with that experimentally established from dependences lnρ(1/T). It is shown that when the Ga impurity atom (4s24p1) occupies the 4b sites of Sn atoms (5s25p2), structural defects of both acceptor nature and donor nature in the form of vacancies in the 4b site are simultaneously generated. The results are discussed in the scope of the Shklovskii–Efros model of a heavily doped and compensated semiconductor.

Electronic Structure and Optical Absorption Spectra of C–Cr Co‐Doped Anatase TiO2 Based on First Principles

The geometrical structure, defect formation energies, electrical and optical properties of C and/or Cr doped anatase TiO2 are calculated by GGA + U method under the framework of density functional theory. The relationship between band structure and light absorption is revealed. The results show that the lattice is obviously distorted after doping, and the stability of C and Cr co‐doping is higher than just Cr doping, second only to Cr doped TiO2. The contribution of C is forming impurity energy levels, and the contribution of Cr is to reduce the band gap in the single doped system. In the co‐doped system, Cr atoms are used as donor impurities and C atoms act as acceptor impurities. The impurity energy is composed of C 2p and Cr 3d orbital hybridization, which reduces the band gap and promotes the separation of the impurity levels. C and Cr co‐doping expands the light absorption of TiO2 to the entire visible region, thereby increasing the absorption coefficient and effectively enhancing the photocatalytic efficiency.

Doping mechanism in novel semiconductor materials

Doping is a key technology in modern semiconductor industry. With reduced size of semiconductor devices, quantum effect becomes significant, and the classic theory for device design will no longer be valid. Thus the traditional doping technology is facing a great challenge. On the other hand, the third generation wide-gap semiconductors like GaN, ZnO and TiO2 have great application potential in optoelectronics and microelectronics due to their wide band gap, direct gap character and good stability. However, there is a doping bottleneck on the p-type doping of these materials. In the field of application of semiconductor technology, doping mechanism in photocatalysis, spintronic materials, and novel two-dimensional (2D) semiconductors are also the frontier of research. The research in this project focuses on the above key topics. The primary discoveries include the follows: (i) Based on first-principles band structure calculations and analysis of the band-edge wave function characters, we proposed that passivated (Mo+C)-doped TiO2 is a strong candidate for hydrogen production through water splitting. The results received highly attention from the experts in the field of photocatalysis, and the feasibility was confirmed by recent experimental studies. (ii) We discovered that the presence of spontaneous magnetization in nitrides and oxides with sufficient holes is an intrinsic property of these first-row d0 semiconductors. The origin and enhancement of such hole-induced ferromagnetism is studied, which suggested new possibility of preparing non-magnetically doped spintronic semiconductor devices. (iii) We systematically studied the doping mechanism and bottleneck of donor and acceptor impurities in quantum dots and quantum wires. Due to the effect of quantum confinement effect, the energy of the conduction band minimum (CBM) increases whereas that of the valence and maximum (VBM) decreases. We found that defect formation energy and transition energy level increase when the size of the quantum dot (QD) decreases, leading to the self-purification effect and degrade the performance of devices. Focused on this problem, we proposed the approach of overcoming the doping bottleneck in nanostructures, and developed a model to describe the quantum Stark effect in hole impurity state of quantum dots. These works promoted the research in the application of nano-devices. (iv) For the first time, the band alignment between two-dimensional transition-metal dichalcogenides MX2 (M=Mo, W; X=S, Se, Te) is calculated. We predicted the type-II band alignment in MoX2/WX2 heterostructures. In addition, direct-indirect gap transition and semiconductor-metal transition in strained MoS2 is observed. Moreover, we studied the mechanical, optical properties and band gap modulation of graphyne, a new allotrope of carbon, and discovered that Ca-doped graphyne had high capacity of hydrogen storage. The project has attracted great attentions, and the related publications are highly cited by researchers all over the world. These works bring better understanding of semiconductor doping theory, and have important scientific value for the device design and property prediction of new generation semiconductors and nano-devices.

Thermoelectric properties of PbTe films and PbTe-based superlattices

The electrical conductivity, Seebeck coefficient, and thermoelectric conversion efficiency of n- and p-type PbTe were calculated over the temperature range of 300-800K by using Boltzmann transport theory and relaxation time approximation, and they were compared with experimental results. A three band model for PbTe was used and alloy scattering from donor or acceptor impurities was included to explain a low electrical mobility at high carrier concentration region exceed 1×1019 cm-3 as well as scatterings from the deformation potential of the acoustic and optical phonons, screened polar optical phonon, and ionized impurity. Nonparabolicity and anisotropy of the L-point valleys were took into account in the calculation. The nonparabolicity and resultant enhancement of the effective masses resulted in the large temperature dependence of conductivity in n-type PbTe. A large Seebeck coefficient in highly p-type PbTe was explained by heavy effective masses in Σ valleys, and carrier mobility of the heavily doped sample was simulated by assuming large deformation potentials for Bi donor and Tl, Na, and K acceptor impurities. Electrical conductivity, Seebeck coefficients and power factors for EuTe/PbTe superlattice and GeS/PbTe amorphous / epitaxial superlattice were also presented and discussed here.

Получение электроимпульсным плазменным спеканием термоэлектрических материалов на основе Si и Ge

AbstractThermoelectric materials on the basis of SiGe produced by spark plasma sintering are studied. The degree of doping of the initial materials, the degree of mixing of Si and Ge, and the properties of the grain structure of the formed samples are varied. It is established that the use of initial materials doped with donor or acceptor impurities provides a means for controlling the charge-carrier concentration in the sintered samples. It is shown that the charge-carrier concentration has the most profound effect on the energy characteristics (power factor) of thermoelectrics. For structures with the highest charge-carrier concentration, the thermoelectric coefficients can be controlled by varying the degree of mixing of Ge and Si and the degree of uniformity of the distribution of impurities.

Fabrication of Tin Oxide Thin Film Transistors by RF Magnetron Sputtering Using Sn/SnO Composite Target

P-type tin oxide thin film deposited by RF sputtering for transparent thin film transistor (TFT) applications is the subject of this study. P-type tin oxide thin film can be made by doping a cation with a lower valence into n-type SnO 2 as an acceptor impurity or by fabrication with tin monoxide (SnO). The later method was investigated in this study by RF magnetron sputtering process, which has a high deposition rate, uniform thickness control, simple stoichiometry control, and reproducibility. A Sn/SnO composite target was used in RF sputtering to utilize the benefits of both metallic and ceramic sputtering targets. A Sn/SnO composite target is expected to provide p-type tin oxide thin films that are easier to manufacture than metallic target or ceramic target. The metallic Sn element provides an excellent control of structural defects, while the ceramic SnO element provides stable stoichiometry. The p-type tin oxide thin film with a Sn/SnO composite target showed very good transparency of ~95%. and excellent electrical properties. The p-type tin oxide thin film of 15nm thickness had a carrier concentration of 8.03X10 15 cm -3 and a mobility of 15.2cm 2 /Vs. With these ultrathin tin oxide films, a p-channel TFT was fabricated with a staggered bottom-gate structure, and the effect of different channel thicknesses and different distances between the two electrodes were evaluated. The tin oxide TFT with a thick p-channel layer showed a significant increase in current measured than the tin oxide with a thin p-channel layer. The current measured tended to increase greatly as the distance between electrodes decreased. The IV output curves of the tin oxide TFTs exhibited characteristics of bipolar transistors potentially due to the partial creation of the oxygen-deficient SnO 2 like structure, but the mechanism of bipolar transistor characteristics from the p-channel tin oxide TFT is still unclear. The fabrication of highly transparent tin oxide thin film with bipolar transistor characteristics is demonstrated herein.

Механизм генерирования донорно-акцепторных пар при сильном легировании n-ZrNiSn акцепторной примесью Ga

AbstractThe nature of the mechanism of the simultaneous generation of donor–acceptor pairs under heavy doping of n -ZrNiSn intermetallic semiconductor with the Ga acceptor impurity is established. Such spatial arrangement in the crystal lattice of ZrNiSn_1– x Ga_ x is found when the rate of movement of the Fermi level εF found from calculations of the density distribution of electron states coincides with that experimentally established from dependences lnρ(1/ T ). It is shown that when the Ga impurity atom (4 s ^24 p ^1) occupies the 4 b sites of Sn atoms (5 s ^25 p ^2), structural defects of both acceptor nature and donor nature in the form of vacancies in the 4 b site are simultaneously generated. The results are discussed in the scope of the Shklovskii–Efros model of a heavily doped and compensated semiconductor.

Уровни зарядового перехода акцепторных примесей в кристаллах ZnO.Расчеты из первых принципов

Уровни зарядового перехода акцепторных примесей в кристаллах ZnO.Расчеты из первых принципов

Electronics properties of ZnSe nanotube with substitutional impurity atoms - A first-principles investigation

The band structure of pristine zinc selenide (ZnSe) nanotube, gallium, chlorine, nitrogen and arsenic substituted ZnSe nanotube are studied using density functional theory (DFT) with GGA/PBE exchange correlation functional. The state of the art of this work is to study the electronic properties of ZnSe nanotubes with substitution impurities. The ZnSe nanotube electronic properties are studied in terms of band structures and density of states spectrum. The band structure of pure ZnSe nanotube shows a semiconducting nature. The gallium, chlorine, nitrogen and arsenic substituted ZnSe structured results in metallic behavior. The density of states provides the insight for the localization of charges in the valence band and conduction band. The substitution of chlorine and nitrogen enhance the density of charges in valence band. We found that nitrogen is the most efficient acceptor impurity for p-type doping, while chlorine is the most suitable impurity for n-type doping. The results of the present work provide a clear vision to tailor the band structure of ZnSe nanotube with substitution impurity. This study is useful to researchers investigating p- and n-type doping as well as optoelectronic device manufacturers.

Rapid, controllable, one-pot and room-temperature aqueous synthesis of ZnO:Cu nanoparticles by pulsed UV laser and its application for photocatalytic degradation of methyl orange.

Zinc oxide (ZnO) and ZnO:Cu nanoparticles (NPs) were synthesized using a rapid, controllable, one-pot and room-temperature pulsed UV-laser assisted method. UV-laser irradiation was used as an effective energy source in order to gain better control over the NPs size and morphology in aqueous media. Parameters effective in laser assisted synthesis of NPs such as irradiation time and laser shot repetition rate were optimized. Photoluminescence (PL) spectra of ZnO NPs showed a broad emission with two trap state peaks located at 442 and 485nm related to electronic transition from zinc interstitial level (IZn ) to zinc vacancy level (VZn ) and electronic transition from conduction band to the oxygen vacancy level (VO ), respectively. For ZnO:Cu NPs, trap state emissions disappeared completely and a copper (Cu)-related emission appeared. PL intensity of Cu-related emission increased with the increase in concentration of Cu2+ , so that for molar ratio of Cu:Zn 2%, optimal value of PL intensity was obtained. The photocatalytic activity of Cu-doped ZnO revealed 50 and 100% increasement than that of undoped NPs under UV and visible irradiation, respectively. The enhanced photocatalytic activity could be attributed to smaller crystal size, as well as creation of impurity acceptor levels (T2 ) inside the ZnO energy band gap.

Analysing impact of oxygen and water exposure on roll-coated organic solar cell performance using impedance spectroscopy

In this work we study the degradation of roll-coated flexible inverted organic solar cells in different atmospheres. We demonstrate that impedance spectroscopy is a powerful tool for elucidating degradation mechanisms; it is used here to distinguish the different degradation mechanisms due to water and oxygen. Identical cells were exposed to different accelerated degradation environments using water only, oxygen only, and both water and oxygen simultaneously, all of them enhanced with UV light. The photocurrent is dramatically reduced in the oxygen-degraded samples. Impedance measurements indicate that this phenomenon is attributed to defects introduced by absorption of oxygen, which results in an increase of the acceptor impurity (NA) at the cathode interface obtained from a Mott-Schottky analysis. Simultaneously, at the anode interface where PEDOT:PSS is not shielded by the substrate, the nature of degradation differs for the water and oxygen degraded samples. While oxygen + UV light decreases the conductivity of the PEDOT:PSS layer, water + UV light changes the PEDOT:PSS work function inducing a depletion region at the anode.

Control of circular polarization of electroluminescence in spin light-emitting diodes based on InGaAs/GaAs/δ〈Mn〉 heterostructures

Circularly polarized luminescence of light-emitting InGaAs/GaAs structures with a delta-doped Mn layer in a GaAs barrier was studied. The structural parameters were varied by different ways, among them are homogeneous and delta-doping with acceptor impurity, and removal of donor doping from the technological process. As it was found, the magnitude and polarity of the degree of circular polarization of luminescence strongly depend on the technological mode chosen. Simultaneous modeling of wave functions of structures highlights a good agreement between the parameters of circularly polarized luminescence and spatial distribution of wave functions of heavy holes relative to the Mn delta-layer.

Structure of a Novel Spinel Li0.5Zn5/3Sb2.5/3O4 by Neutron and Synchrotron Diffraction Analysis

Zn7/3Sb2/3O4 is a secondary phase in ZnO-based varistors. Acceptor impurities, such as Li+, increase the resistivity. This effect is produced by a modification of the grain boundary barriers. The role of the cationic distribution in the mentioned events is worth clarifying. The Li0.5Zn5/3Sb2.5/3O4 room-temperature structure was determined by means of a neutron diffraction and synchrotron X-ray diffraction investigation. The title compound was prepared by conventional ceramic process. The elemental composition of the investigated sample was verified by means of electron microscopy—energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. The neutron experiment was performed at the high-intensity neutron diffractometer with position-sensitive detector at the D1B beamline of the Laue-Langevin Institute, Grenoble. The high resolution synchrotron measurement was carried out at MCX beamline of Elettra Sincrotrone Trieste. Rietveld analysis was performed with the FullProf program. Li0.5Zn5/3Sb2.5/3O4 belongs to the spinel family, space group F d 3 ¯ m (227). The measured lattice parameter is a = 8.5567(1) Å. The Li+1 and Zn+2 ions are randomly distributed among the tetrahedral and octahedral sites as opposed to Sb+5 ions which have preference for octahedral sites. Fractional coordinate of oxygen, u = 0.2596(1), indicates a slight deformation of the tetrahedral and octahedral sites. The data given in this paper provide structural support for further studies on measurements and microscopic explanations of the interesting properties of this family of compounds.

Sensitivity of Breakdown Voltage of Power Transistors to Dopant Impurities

To increase the breakdown voltage (BV) and, in the same time, decrease the on-state voltage (OSV) of wide-band gap transistors it is essential to carefully design the doping profile of these transistors in order to decrease the resistivity of the material during the on-state current flow and decrease the impact ionization generation rate in regions with high electric field during off-state. In general, the two problems depend on each other and there is trade-off between the increasing the BV and decreasing the OSV [1]. In this article we will analyze this tradeoff by using the formalism of doping sensitivity functions of the BV and OSV. These functions show how sensitive the BV and OSV are to infinitesimal variations of the acceptor or donor impurities inside the semiconductor. For instance, the doping sensitivity function of the BV, gBV(r), shows how much the BV increases by adding one donor impurity at location r inside the device. Similarly, the doping sensitivity function of the OSV, gOSV(r), shows how much the OSV increases by adding one donor impurity at location r inside the device. As we have shown in [2, 3], the doping sensitivity functions are instrumental in the optimization of WBG power devices. The doping sensitivity functions of the BV and OSV can be computed efficiently by using the adjoint method. Once these functions are computed they can be coupled with gradient-based optimization methods to estimate the optimum doping profiles for acceptors, Na(r), and donors, Nd(r), in order to increase the BV and decreases the OSV. At the conference we will describe the numerical implementation of the adjoint method for the optimization of WBG power devices and present simulation results for a vertical and horizontal SiC MOSFETs. More importantly, we will show that in general, in wide-band-gap MOSFETs and IGBTs, the doping sensitivity functions of the BV and OSV, gBV(r) and gOSV(r), respectively, and are not linearly dependent. Therefore, from a mathematical point of view, the BV and OSV are quantities that can be controlled independently by changing the doing profiles inside the transistor. Different equivalent ways to define and compute the doping sensitivity functions of BV and OSV will also be presented. The different definitions of the doping sensitivity functions will be compared to each other and the computational complexity will be discussed in each case. [1] J. Baliga, Fundamentals of Power Semiconductor Devices: Springer, 2008. [2] P. Andrei, "Using Doping Sensitivity Functions to Optimize Power Transistors," IEEE Workshop on Microelectronics and Electron Devices (WMED), Boise, ID, 2015. [3] C. Zhu and P. Andrei, “Adjoint Method for Increasing the Breakdown Voltage and Reducing the On-State Resistance in Wide Band”, 231 ECS Meeting, New Orleans, 2017. [4] P. Andrei and L. Oniciuc, "Suppressing Random Dopant-Induced Fluctuations of Threshold Voltages in Semiconductor Devices," Journal of Applied Physics, vol. 104, Art. No. 104508, 2008.