This document calculates and compares the electron mobility in wurtzite (WZ) and zincblende (ZB) forms of aluminum nitride (AlN) using an iterative method. It solves the Boltzmann transport equation taking into account various scattering mechanisms between 100-600K. Total scattering rates in WZ-AlN are higher than in ZB-AlN due to differences in bandgap and electron effective mass. Electron mobility is higher in WZ-AlN (337.61 cm2/V-s at 300K) than ZB-AlN (152.254 cm2/V-s) and decreases with increasing temperature and electron concentration in both structures.
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
I show how much GW corrections are important not only for the band structure but also in the calculation of the electron-phonon matrix elements. I present different examples and comparison with the experimental results.
Optical spectroscopy techniques such as transmission, reflection, absorption, and photoluminescence measurements are important tools for characterizing the optical properties of semiconductor materials for photovoltaic applications. These techniques can determine the band gap type and energy, which are crucial for a material's suitability as a solar cell absorber. A direct band gap is preferable to an indirect band gap. Temperature-dependent absorption measurements provide insight into the temperature dependence of the band gap and allow comparison to density functional theory calculations. Characterizing defects through photoluminescence is also useful. Together, optical measurements provide essential information for understanding and improving photovoltaic materials.
This document discusses using advanced computational methods beyond density functional theory (DFT) to more accurately model electron-phonon coupling (EPC) in graphene. It finds that the GW approximation provides a better description of phonon dispersions and EPC than DFT. Hybrid functionals can also reproduce GW results if the amount of nonlocal exchange is tuned. The EPC is found to decrease with doping as screening becomes stronger. Experimental evidence generally agrees with the computational results.
An introduction to the fundamental physics of transparent conducting oxides including a review of the electrical and optical properties of common materials.
This document describes the tight-binding method for calculating the energy diagram of nanoelectronic systems. It introduces the tight-binding method and its application to calculating the energy diagrams of polyacetylene, single-layer graphene, bilayer graphene, and multi-layer graphene. It also discusses using the tight-binding method to calculate the energy diagrams of two and four layer graphene in a constant electric field and single-layer graphene in a modulated electric field. The document provides the theoretical framework and mathematical equations for applying the tight-binding method to these different nanoscale systems.
This document discusses graphene MOSFETs and their potential for post-silicon electronics. It summarizes that graphene has zero bandgap, which prevents switching, but the bandgap can be modified through nanoribbons, bilayers, or strain. Graphene MOSFETs have been fabricated with exfoliated or epitaxial graphene using various dielectrics and show high mobility but low on-off ratios. While graphene's properties are promising for high-speed devices, opening a bandgap comparable to silicon would decrease mobility and hinder low-power applications. Overall, graphene transistors continue to be explored but challenges remain for practical logic devices to replace silicon MOSFETs.
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
I show how much GW corrections are important not only for the band structure but also in the calculation of the electron-phonon matrix elements. I present different examples and comparison with the experimental results.
Optical spectroscopy techniques such as transmission, reflection, absorption, and photoluminescence measurements are important tools for characterizing the optical properties of semiconductor materials for photovoltaic applications. These techniques can determine the band gap type and energy, which are crucial for a material's suitability as a solar cell absorber. A direct band gap is preferable to an indirect band gap. Temperature-dependent absorption measurements provide insight into the temperature dependence of the band gap and allow comparison to density functional theory calculations. Characterizing defects through photoluminescence is also useful. Together, optical measurements provide essential information for understanding and improving photovoltaic materials.
This document discusses using advanced computational methods beyond density functional theory (DFT) to more accurately model electron-phonon coupling (EPC) in graphene. It finds that the GW approximation provides a better description of phonon dispersions and EPC than DFT. Hybrid functionals can also reproduce GW results if the amount of nonlocal exchange is tuned. The EPC is found to decrease with doping as screening becomes stronger. Experimental evidence generally agrees with the computational results.
An introduction to the fundamental physics of transparent conducting oxides including a review of the electrical and optical properties of common materials.
This document describes the tight-binding method for calculating the energy diagram of nanoelectronic systems. It introduces the tight-binding method and its application to calculating the energy diagrams of polyacetylene, single-layer graphene, bilayer graphene, and multi-layer graphene. It also discusses using the tight-binding method to calculate the energy diagrams of two and four layer graphene in a constant electric field and single-layer graphene in a modulated electric field. The document provides the theoretical framework and mathematical equations for applying the tight-binding method to these different nanoscale systems.
This document discusses graphene MOSFETs and their potential for post-silicon electronics. It summarizes that graphene has zero bandgap, which prevents switching, but the bandgap can be modified through nanoribbons, bilayers, or strain. Graphene MOSFETs have been fabricated with exfoliated or epitaxial graphene using various dielectrics and show high mobility but low on-off ratios. While graphene's properties are promising for high-speed devices, opening a bandgap comparable to silicon would decrease mobility and hinder low-power applications. Overall, graphene transistors continue to be explored but challenges remain for practical logic devices to replace silicon MOSFETs.
Impact of electronic correlation on the electron-phonon couplingClaudio Attaccalite
1) Electronic correlation effects are not fully captured by DFT calculations of electron-phonon coupling (EPC). GW and hybrid functional methods can provide corrections.
2) GW calculations have shown that EPC values can be underestimated or overestimated by DFT. Correlation effects can also lead to new physics in EPC.
3) Simplified approaches have been developed to approximate GW corrections to EPC in order to reduce computational cost, such as using static screening or thermal averaging. These approaches have been shown to improve predictions of properties like phonon dispersions and superconducting transition temperatures.
This document summarizes the properties and electronic structure of graphene and graphene nanoribbons. It describes how graphene was first theorized in the 1950s but not isolated until 2004. Graphene has exceptional properties such as strength, flexibility, and electron mobility. Confining graphene into nanoribbons can open a bandgap, making it suitable for field effect transistors. The bandgap increases as the nanoribbon width decreases. Graphene nanoribbon field effect transistors could have applications in logic devices and memory due to tunable bandgaps and higher performance compared to devices using only graphene.
The driving engine for the exponential growth of digital information processing systems is scaling down the transistor dimensions. For decades, this has enhanced the device performance and density. However, the International Technology Roadmap for Semiconductors (ITRS) states the end of Moore’s law in the next decade due to the scaling challenges of silicon-based CMOS electronics, e.g. extremely high power density. The forward-looking solutions are the utilization of emerging materials and devices for integrated circuits, e.g. carbon-based materials. The presentation of my Ph.D. work focuses on graphene, one atomic layer of carbon sheet, experimentally discovered in 2004. Since fabrication technology of emerging materials is still in early stages, transistor modeling has been playing an important role for evaluating futuristic graphene-based devices and circuits. The device has been simulated by solving a quantum transport model based on non-equilibrium Green’s function (NEGF) approach, which fully treats short channel-length electrostatic effects and the quantum tunneling effects, leading to the technology exploration of graphene nanoribbon field effect transistors (GNR FETs) for the future. This research presents a comprehensive study of the width-dependence performance of the GNR FETs and the scaling of its channel length down to 2.5 nanometer, investigating its potential use beyond-CMOS emerging technology.
Journal Molecular Crystals and Liquid Crystals (1994), Vol. 256, pp. 555-561.
S. A. Jeglinski, M. E. Hollier, J. F. Gold, and Z. V. Vardeny
University of Utah, Physics Department, Salt Lake City, UT 84112
Y. Ding and T. Barton
Iowa State University, Chemistry Department, Ames, IA 50011
Abstract
A diode has been fabricated with poly(phenylene acetylene) [PPA] as the electroluminescent polymer. The device exhibited an unusual symmetric (positive and negative bias) I-V characteristic and electroluminescent output. These experimental results are discussed in terms of tunneling of electrons and holes via localized states.
This document discusses several theories related to colloid stability and flocculation, including the Gouy-Chapman theory, Schultz-Hardy rule, and Stern adsorption theory. The Gouy-Chapman theory and Schultz-Hardy rule describe how the valence of counterions affects the critical flocculation concentration, with higher valences requiring lower concentrations. Stern adsorption theory introduces the concept of a Stern layer to account for specific ion adsorption at surfaces, improving upon diffuse double layer models at high concentrations.
The document discusses graphene and its potential use in transistors. It describes graphene as a single sheet of carbon atoms arranged in a honeycomb lattice. Researchers have shown that stacking a few layers of graphene could enable optical switches that are 100 times faster than current technologies. The document also details experiments where graphene field-effect transistors were fabricated with gate lengths down to 150nm, achieving a cutoff frequency of 26GHz. Scaling to smaller gate lengths allows higher frequencies, with cutoff frequency scaling inversely with the square of the gate length. Graphene has potential for high-frequency and versatile applications due to its high carrier mobility and small channel lengths.
The document compares the low field electron transport properties in compounds of groups III-V semiconductors by solving the Boltzmann equation using an iterative technique. It calculates the temperature and doping dependencies of electron mobility in InP, InAs, GaP and GaAs. The electron mobility decreases with increasing temperature from 100K to 500K for each material due to increased electron-phonon scattering. Electron mobility also increases significantly with higher doping concentration at low temperatures. The iterative results show good agreement with other calculations and experiments. Electron mobility is highest in InAs and lowest in GaP at 300K, due to differences in their effective masses.
Electronic bands structure and gap in mid-infrared detector InAs/GaSb type II...IJERA Editor
We present here theoretical study of the electronic bands structure E (d1) of InAs (d1=25 Å)/GaSb (d2=25 Å) type
II superlattice at 4.2 K performed in the envelope function formalism. We study the effect of d1 and the offset ,
between heavy holes bands edges of InAs and GaSb, on the band gap Eg (), at the center of the first Brillouin
zone, and the semiconductor-to-semimetal transition. Eg (, T) decreases from 288.7 meV at 4.2 K to 230 meV
at 300K. In the investigated temperature range, the cut-off wavelength 4.3 m ≤ c ≤ 5.4 m situates this sample
as mid-wavelength infrared detector (MWIR). Our results are in good agreement with the experimental data
realized by C. Cervera et al.
1. The document discusses advances in impedance spectroscopy for analyzing solar energy conversion devices like dye-sensitized solar cells.
2. Impedance spectroscopy allows measurement of resistances and capacitances in solar cells, which provides insight into recombination, diffusion lengths, and energetics.
3. Parameters like the chemical capacitance, recombination resistance, and diffusion coefficient can be extracted and related to performance factors like open-circuit voltage, short-circuit current, and fill factor.
This document analyzes the electrical properties of aluminum/zinc oxide/aluminum thin films prepared by thermal evaporation at different annealing temperatures. It finds that:
1) The films' AC conductivity obeys a power law relationship with frequency and the exponent decreases with increasing annealing temperature, indicating correlated barrier hopping is the dominant conduction mechanism.
2) Both the dielectric constant and loss factor increase with rising frequency and annealing temperature.
3) Cole-Cole diagrams show single relaxation mechanisms are present, and polarization increases with higher annealing temperatures, suggesting a polydisperse dielectric response.
4) Overall, the study characterizes how annealing temperature affects the AC conductivity and dielectric properties of the ZnO thin
This document discusses the optimization and simulation of Josephson junctions as switching elements. It begins with an introduction stating the need to optimize Josephson junction parameters and characteristics to increase switching speed. It then provides a brief review of the Josephson effect and properties of Josephson junctions. The rest of the document details a theoretical approach to estimating junction parameters, characteristics, and optimization methods, and using computer simulation to model the dynamic response of Josephson junctions to better understand their switching performance and speed.
This document summarizes a conference presentation on conducting polymer nanofibers and graphene. It discusses how polyacetylene nanofibers have intrinsic conductivity similar to metals. It also summarizes the 2010 Nobel Prize in Physics that was awarded for the discovery of graphene, a single layer of carbon atoms with unusual electronic properties. The document concludes by describing several methods for producing graphene sheets, including mechanical exfoliation of graphite and chemical vapor deposition.
Surface carrier recombination of a si tip under high electric fieldbmazumder
Using laser assisted atom probe tomography, the authors investigated surface recombination processes of a silicon tip under high electric field by changing the laser wavelength. They found that with infrared laser light, the evaporation rate showed a wide peak indicating a long electron-phonon relaxation time at the surface. However, with green laser light, the silicon peaks in the ion flight time spectrum were well resolved even at high laser intensity, demonstrating that this behavior is common to indirect bandgap semiconductors. The authors developed a simple model to explain the laser wavelength dependence and estimate the surface recombination time.
- The document discusses quantum wires and quantum dots.
- For quantum wires, electrons are confined in two directions and free to move in the third, resulting in a 1D electron gas. The wave function and energy levels depend on the confinement potential.
- For quantum dots, the potential confines electrons in all three dimensions, resulting in discrete energy levels. The wave function is a product of sine waves and the energy depends on quantum numbers in each dimension.
Electronic structure of strongly correlated materials Part III V.AnisimovABDERRAHMANE REGGAD
This document discusses results from DFT+DMFT calculations on various strongly correlated materials. It summarizes calculations showing a strongly correlated metal state in SrVO3 with a lower Hubbard band, a Mott insulator transition in V2O3 accompanied by a small structural change, and heavy fermion behavior in Li2VO4 without f-electrons. It also discusses calculations of the charge transfer insulator NiO, pressure-induced transitions in MnO and Fe2O3, correlated covalent insulators FeSi and FeSb2, superconductivity in LaOFeAs, Jahn-Teller distortions and orbital ordering in KCuF3, and f-electron localization in cerium. The document
This document summarizes research on photovoltaic structures using thermally evaporated tin sulfide thin films. Key points:
- Tin sulfide films were deposited by thermal evaporation onto glass substrates in thicknesses ranging from 100-300nm.
- The films exhibited n-type conductivity at low thicknesses, transitioning to p-type at higher thicknesses. Bandgaps ranged from 2.1-1.7eV.
- CdS/SnS photovoltaic cells showed open circuit voltages up to 400mV, short circuit current densities up to 0.061mA/cm2, and conversion efficiencies up to 1.49% under 106mW/cm2 illumination.
Performance Analysis of Single Quantum Dots and Couple Quantum Dots at Interm...IOSR Journals
This document analyzes the performance of single quantum dots versus coupled quantum dots in intermediate band solar cells through simulations. It finds that increasing the distance between quantum dots reduces the overlap between their wave functions, decreasing the intermediate bandwidth. A narrower intermediate band is inversely related to cell efficiency. Specifically, simulations show that decreasing the barrier width between quantum dots from 6nm to 2nm while keeping their width at 4nm increases the intermediate bandwidth from a very thin level to 90meV, improving efficiency.
Graphene is a single layer of carbon atoms arranged in a hexagonal lattice. It is the basic structural element of other allotropes like graphite, which can be viewed as stacked layers of graphene. Graphene is highly electrically conductive due to the unique electronic band structure arising from its hexagonal lattice. It also has very high thermal conductivity and mechanical strength. Doping graphene is motivated to modify its properties and enable applications by introducing a bandgap. Plasmonic effects arise from the collective oscillation of free electrons in metal nanoparticles, which can enhance light absorption and be used to integrate graphene with photonic applications.
This document discusses using the Taguchi method to optimize welding parameters for shielded metal arc welding of steel pipes to produce leak-proof joints. Key welding parameters like current, speed, electrode angle, and root gap were selected. Experiments were conducted according to an L9 orthogonal array, and ANOVA was used to analyze the results. The analysis found that current had the highest contribution to leaks at 44.85%, while electrode angle contributed 30.21%. Three optimal combinations of parameters that produced no leaks were identified. The study demonstrated that the Taguchi method can be used to optimize welding parameters and nullify the effects of noise to consistently produce leak-proof pipe welds.
The document describes the design and development of a mechanism for detecting rotating metallic objects using inductive proximity switches. The system was designed to operate in dusty and muddy environments. Various sensors were tested and inductive proximity sensors were selected as they can detect metals, operate in harsh environments, and have a moderate sensing range of up to 50mm. An experimental setup was built with a rotating drum to simulate the operating conditions. Tests were performed with different sensor distances and speeds. The results showed the system successfully detected the presence and absence of metallic objects rotating at speeds up to 600rpm in dusty and muddy conditions within the sensing range of the sensors.
Impact of electronic correlation on the electron-phonon couplingClaudio Attaccalite
1) Electronic correlation effects are not fully captured by DFT calculations of electron-phonon coupling (EPC). GW and hybrid functional methods can provide corrections.
2) GW calculations have shown that EPC values can be underestimated or overestimated by DFT. Correlation effects can also lead to new physics in EPC.
3) Simplified approaches have been developed to approximate GW corrections to EPC in order to reduce computational cost, such as using static screening or thermal averaging. These approaches have been shown to improve predictions of properties like phonon dispersions and superconducting transition temperatures.
This document summarizes the properties and electronic structure of graphene and graphene nanoribbons. It describes how graphene was first theorized in the 1950s but not isolated until 2004. Graphene has exceptional properties such as strength, flexibility, and electron mobility. Confining graphene into nanoribbons can open a bandgap, making it suitable for field effect transistors. The bandgap increases as the nanoribbon width decreases. Graphene nanoribbon field effect transistors could have applications in logic devices and memory due to tunable bandgaps and higher performance compared to devices using only graphene.
The driving engine for the exponential growth of digital information processing systems is scaling down the transistor dimensions. For decades, this has enhanced the device performance and density. However, the International Technology Roadmap for Semiconductors (ITRS) states the end of Moore’s law in the next decade due to the scaling challenges of silicon-based CMOS electronics, e.g. extremely high power density. The forward-looking solutions are the utilization of emerging materials and devices for integrated circuits, e.g. carbon-based materials. The presentation of my Ph.D. work focuses on graphene, one atomic layer of carbon sheet, experimentally discovered in 2004. Since fabrication technology of emerging materials is still in early stages, transistor modeling has been playing an important role for evaluating futuristic graphene-based devices and circuits. The device has been simulated by solving a quantum transport model based on non-equilibrium Green’s function (NEGF) approach, which fully treats short channel-length electrostatic effects and the quantum tunneling effects, leading to the technology exploration of graphene nanoribbon field effect transistors (GNR FETs) for the future. This research presents a comprehensive study of the width-dependence performance of the GNR FETs and the scaling of its channel length down to 2.5 nanometer, investigating its potential use beyond-CMOS emerging technology.
Journal Molecular Crystals and Liquid Crystals (1994), Vol. 256, pp. 555-561.
S. A. Jeglinski, M. E. Hollier, J. F. Gold, and Z. V. Vardeny
University of Utah, Physics Department, Salt Lake City, UT 84112
Y. Ding and T. Barton
Iowa State University, Chemistry Department, Ames, IA 50011
Abstract
A diode has been fabricated with poly(phenylene acetylene) [PPA] as the electroluminescent polymer. The device exhibited an unusual symmetric (positive and negative bias) I-V characteristic and electroluminescent output. These experimental results are discussed in terms of tunneling of electrons and holes via localized states.
This document discusses several theories related to colloid stability and flocculation, including the Gouy-Chapman theory, Schultz-Hardy rule, and Stern adsorption theory. The Gouy-Chapman theory and Schultz-Hardy rule describe how the valence of counterions affects the critical flocculation concentration, with higher valences requiring lower concentrations. Stern adsorption theory introduces the concept of a Stern layer to account for specific ion adsorption at surfaces, improving upon diffuse double layer models at high concentrations.
The document discusses graphene and its potential use in transistors. It describes graphene as a single sheet of carbon atoms arranged in a honeycomb lattice. Researchers have shown that stacking a few layers of graphene could enable optical switches that are 100 times faster than current technologies. The document also details experiments where graphene field-effect transistors were fabricated with gate lengths down to 150nm, achieving a cutoff frequency of 26GHz. Scaling to smaller gate lengths allows higher frequencies, with cutoff frequency scaling inversely with the square of the gate length. Graphene has potential for high-frequency and versatile applications due to its high carrier mobility and small channel lengths.
The document compares the low field electron transport properties in compounds of groups III-V semiconductors by solving the Boltzmann equation using an iterative technique. It calculates the temperature and doping dependencies of electron mobility in InP, InAs, GaP and GaAs. The electron mobility decreases with increasing temperature from 100K to 500K for each material due to increased electron-phonon scattering. Electron mobility also increases significantly with higher doping concentration at low temperatures. The iterative results show good agreement with other calculations and experiments. Electron mobility is highest in InAs and lowest in GaP at 300K, due to differences in their effective masses.
Electronic bands structure and gap in mid-infrared detector InAs/GaSb type II...IJERA Editor
We present here theoretical study of the electronic bands structure E (d1) of InAs (d1=25 Å)/GaSb (d2=25 Å) type
II superlattice at 4.2 K performed in the envelope function formalism. We study the effect of d1 and the offset ,
between heavy holes bands edges of InAs and GaSb, on the band gap Eg (), at the center of the first Brillouin
zone, and the semiconductor-to-semimetal transition. Eg (, T) decreases from 288.7 meV at 4.2 K to 230 meV
at 300K. In the investigated temperature range, the cut-off wavelength 4.3 m ≤ c ≤ 5.4 m situates this sample
as mid-wavelength infrared detector (MWIR). Our results are in good agreement with the experimental data
realized by C. Cervera et al.
1. The document discusses advances in impedance spectroscopy for analyzing solar energy conversion devices like dye-sensitized solar cells.
2. Impedance spectroscopy allows measurement of resistances and capacitances in solar cells, which provides insight into recombination, diffusion lengths, and energetics.
3. Parameters like the chemical capacitance, recombination resistance, and diffusion coefficient can be extracted and related to performance factors like open-circuit voltage, short-circuit current, and fill factor.
This document analyzes the electrical properties of aluminum/zinc oxide/aluminum thin films prepared by thermal evaporation at different annealing temperatures. It finds that:
1) The films' AC conductivity obeys a power law relationship with frequency and the exponent decreases with increasing annealing temperature, indicating correlated barrier hopping is the dominant conduction mechanism.
2) Both the dielectric constant and loss factor increase with rising frequency and annealing temperature.
3) Cole-Cole diagrams show single relaxation mechanisms are present, and polarization increases with higher annealing temperatures, suggesting a polydisperse dielectric response.
4) Overall, the study characterizes how annealing temperature affects the AC conductivity and dielectric properties of the ZnO thin
This document discusses the optimization and simulation of Josephson junctions as switching elements. It begins with an introduction stating the need to optimize Josephson junction parameters and characteristics to increase switching speed. It then provides a brief review of the Josephson effect and properties of Josephson junctions. The rest of the document details a theoretical approach to estimating junction parameters, characteristics, and optimization methods, and using computer simulation to model the dynamic response of Josephson junctions to better understand their switching performance and speed.
This document summarizes a conference presentation on conducting polymer nanofibers and graphene. It discusses how polyacetylene nanofibers have intrinsic conductivity similar to metals. It also summarizes the 2010 Nobel Prize in Physics that was awarded for the discovery of graphene, a single layer of carbon atoms with unusual electronic properties. The document concludes by describing several methods for producing graphene sheets, including mechanical exfoliation of graphite and chemical vapor deposition.
Surface carrier recombination of a si tip under high electric fieldbmazumder
Using laser assisted atom probe tomography, the authors investigated surface recombination processes of a silicon tip under high electric field by changing the laser wavelength. They found that with infrared laser light, the evaporation rate showed a wide peak indicating a long electron-phonon relaxation time at the surface. However, with green laser light, the silicon peaks in the ion flight time spectrum were well resolved even at high laser intensity, demonstrating that this behavior is common to indirect bandgap semiconductors. The authors developed a simple model to explain the laser wavelength dependence and estimate the surface recombination time.
- The document discusses quantum wires and quantum dots.
- For quantum wires, electrons are confined in two directions and free to move in the third, resulting in a 1D electron gas. The wave function and energy levels depend on the confinement potential.
- For quantum dots, the potential confines electrons in all three dimensions, resulting in discrete energy levels. The wave function is a product of sine waves and the energy depends on quantum numbers in each dimension.
Electronic structure of strongly correlated materials Part III V.AnisimovABDERRAHMANE REGGAD
This document discusses results from DFT+DMFT calculations on various strongly correlated materials. It summarizes calculations showing a strongly correlated metal state in SrVO3 with a lower Hubbard band, a Mott insulator transition in V2O3 accompanied by a small structural change, and heavy fermion behavior in Li2VO4 without f-electrons. It also discusses calculations of the charge transfer insulator NiO, pressure-induced transitions in MnO and Fe2O3, correlated covalent insulators FeSi and FeSb2, superconductivity in LaOFeAs, Jahn-Teller distortions and orbital ordering in KCuF3, and f-electron localization in cerium. The document
This document summarizes research on photovoltaic structures using thermally evaporated tin sulfide thin films. Key points:
- Tin sulfide films were deposited by thermal evaporation onto glass substrates in thicknesses ranging from 100-300nm.
- The films exhibited n-type conductivity at low thicknesses, transitioning to p-type at higher thicknesses. Bandgaps ranged from 2.1-1.7eV.
- CdS/SnS photovoltaic cells showed open circuit voltages up to 400mV, short circuit current densities up to 0.061mA/cm2, and conversion efficiencies up to 1.49% under 106mW/cm2 illumination.
Performance Analysis of Single Quantum Dots and Couple Quantum Dots at Interm...IOSR Journals
This document analyzes the performance of single quantum dots versus coupled quantum dots in intermediate band solar cells through simulations. It finds that increasing the distance between quantum dots reduces the overlap between their wave functions, decreasing the intermediate bandwidth. A narrower intermediate band is inversely related to cell efficiency. Specifically, simulations show that decreasing the barrier width between quantum dots from 6nm to 2nm while keeping their width at 4nm increases the intermediate bandwidth from a very thin level to 90meV, improving efficiency.
Graphene is a single layer of carbon atoms arranged in a hexagonal lattice. It is the basic structural element of other allotropes like graphite, which can be viewed as stacked layers of graphene. Graphene is highly electrically conductive due to the unique electronic band structure arising from its hexagonal lattice. It also has very high thermal conductivity and mechanical strength. Doping graphene is motivated to modify its properties and enable applications by introducing a bandgap. Plasmonic effects arise from the collective oscillation of free electrons in metal nanoparticles, which can enhance light absorption and be used to integrate graphene with photonic applications.
This document discusses using the Taguchi method to optimize welding parameters for shielded metal arc welding of steel pipes to produce leak-proof joints. Key welding parameters like current, speed, electrode angle, and root gap were selected. Experiments were conducted according to an L9 orthogonal array, and ANOVA was used to analyze the results. The analysis found that current had the highest contribution to leaks at 44.85%, while electrode angle contributed 30.21%. Three optimal combinations of parameters that produced no leaks were identified. The study demonstrated that the Taguchi method can be used to optimize welding parameters and nullify the effects of noise to consistently produce leak-proof pipe welds.
The document describes the design and development of a mechanism for detecting rotating metallic objects using inductive proximity switches. The system was designed to operate in dusty and muddy environments. Various sensors were tested and inductive proximity sensors were selected as they can detect metals, operate in harsh environments, and have a moderate sensing range of up to 50mm. An experimental setup was built with a rotating drum to simulate the operating conditions. Tests were performed with different sensor distances and speeds. The results showed the system successfully detected the presence and absence of metallic objects rotating at speeds up to 600rpm in dusty and muddy conditions within the sensing range of the sensors.
Lista de los libros más vendidos del 27 de junio al 3 de julio de 2013. Realizada por Alberto Berenguer del programa 'De lectura Obligada', Lista de los libros más vendidos en España de ficción y no ficción en formato papel. También los ebooks más vendidos en España según Amazon. Además, los ebooks más vendidos en Reino Unido, Canadá, Francia, Italia, Alemania y Japón.
El documento habla sobre los sistemas de información de mercadeo. Explica que estos sistemas se sustentan en bases de datos de mercadeo que contienen datos recolectados por diversos sistemas como números telefónicos gratuitos, fax, correo electrónico y más. También describe algunos elementos clave de los sistemas de información como ventajas, tipos de sistemas de recolección de datos y programas de lealtad.
El documento presenta conceptos fundamentales relacionados con el medio ambiente, incluyendo definiciones de términos como biodiversidad, ecosistema, contaminación y más. También describe conceptos como emisión, inmisión, vertido y residuo, así como procesos como reutilización, reciclaje, valorización y eliminación. Finalmente, aborda temas como el desarrollo sostenible, el principio de quien contamina paga, y efectos como el efecto invernadero, la lluvia ácida y el agujero de
Este documento trata sobre la relación entre la ciudadanía, las políticas públicas y las tecnologías sociales. Plantea preguntas sobre la participación ciudadana en la elaboración de políticas y servicios públicos a nivel local. También presenta ejemplos de cómo las tecnologías de la información y la comunicación (TIC) pueden facilitar la participación ciudadana y la resolución colaborativa de problemas.
Este documento describe las utilidades de los microorganismos en la lucha contra plagas de insectos y mareas negras, así como en la depuración de aguas residuales. También explica el papel fundamental de los microorganismos en los ciclos biogeoquímicos del carbono y el nitrógeno, que son esenciales para el recambio de materia y energía en la naturaleza.
1) Antonio Callado foi um romancista, dramaturgo e jornalista brasileiro nascido em 1917 que publicou diversos romances e peças de teatro durante sua carreira.
2) Darcy Ribeiro foi um antropólogo, educador e político brasileiro fundador da Universidade de Brasília nascido em 1922, que escreveu obras etnográficas e romances durante sua vida.
3) Castro Alves foi um poeta e pintor brasileiro nascido em 1847 conhecido como um dos maiores nomes da literatura brasile
La educación parvularia en Chile se creó en 1944 para preparar educadoras y brindar aprendizajes óptimos a niños preescolares. Este nivel educativo atiende a niños desde su nacimiento hasta los 6 años de edad con el fin de apoyar a la familia y ofrecer una educación de calidad y acorde a los derechos de los niños, aunque no es obligatoria. La educación parvularia la proveen escuelas municipales, la Junta Nacional de Jardines Infantiles y fundaciones como Integra que atienden a ni
A poema descreve a vida simples e feliz de alguém vivendo no sertão perto de uma mata e ribeirão, com Deus como sua companhia. Ele fala sobre sua casa modesta, observar as estrelas à noite, trabalhar cantando na terra que o inspira, ir à missa e visitar sua amada, e tocar violão ao som da mata.
El documento describe la ubicación y características geográficas de Chile. Chile se encuentra en el extremo suroccidental de América del Sur y posee un largo y estrecho territorio continental que se extiende desde el desierto de Atacama hasta la Isla Grande de Tierra del Fuego. Además de su territorio continental, Chile ejerce soberanía sobre varias islas e islotes en el Océano Pacífico.
This document provides a brief overview of attractions in London including museums such as the British Museum, National Gallery and Tate Gallery. It also mentions parks like St. James Park, Hyde Park and Green Park as well as education and entertainment opportunities. The document conveys greetings and thanks the reader for their attention.
Este documento presenta la información general sobre un curso virtual de gestión ambiental dictado por el docente Arlex Angarita. El objetivo general del curso es identificar las problemáticas ambientales actuales y estrategias de gestión ambiental con enfoque de sustentabilidad. Entre los contenidos se encuentran conceptos básicos de recursos naturales, dinámica ecológica y medio ambiente, así como normatividad, herramientas de diagnóstico e implementación de planes de gestión ambiental. La metodología incluye lecturas, estudios de caso
1) The document discusses future plans and activities using future tense. Common indicators of future tense are words like "tomorrow", "next week", and "next year".
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International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
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International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
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1. H. Arabshahi, M. Izadifard and A. Karimi * / International Journal Of Engineering Research
And Applications (IJERA) ISSN: 2248-9622 WWW.IJERA.COM
Vol. 2, issue 5, september- october 2012, pp.404-407
Calculation of Elecron Mobility in WZ-AlN and ZB-AlN at Low
Electric Field
1
H. Arabshahi, 2M. Izadifard and 2A. Karimi
1
Physics Department, Payame Noor University, Tehran, Iran
2
Physics Department, Shahrood University of Technology, Shahrood, Iran
Abstract
In this work the electron mobility of AlN III-V semiconductor with Wurzite crystalline
Wurtzite and AlN Zincblende semiconductor properties of WZ-AlN , it has a very wide bandgap
compounds were calculated using iterative ,high thermal conductivity and transparency of
method in range of 100-600 K. We compare polar ultraviolet LEDs and high-power electronic devices
optic phonon scattering, deformation-potential for promising material in deep UV devices , white
acoustic phonon scattering, piezoelectric color LED ,high density medical laser ,
scattering and impurity scattering mechanisms. photolithography, photocatalytic decontamination ,
Boltzmann transport equation was solved using alternative of Hg lamp and He-Cd laser . They are
iterative method. In addition, we took into also applied to high-power electronic devices and
account the mixing of wave functions and solar cells.With comparison of scattering effect in
electron screening and we investigated ZB-AlN and WZ-AlN structures, we result that for
temperature dependence of mobility of the given deformation potential scattering, the scattering of
compound. electron increased with increasing the energy. In
piezoelectric scattering with increasing of energy the
Keywords-: AlN Wurtzite , AlN Zincblende scattering decreased in polar optical phonon
,electron mobility , iterative method , III-Nitrides. scattering, the scattering is increasing by increasing
temperature however changes differ is not important
I. INTRODUCTION and in impurity scattering, the scattering rate of
Recently ,the previous studies about III-V electron due to impurities atom in low-temperature
semiconductor compounds are considered important is more than high temperature. Thus, the scattering
III-V semiconductor compounds, InN, GaN and rate of electron in WZ-AlN is more than ZB-AlN
AlN, respectively 1.8 ev,3.4 ev , 6.2 ev , have the wide because their bandgap and the effective mass of
band gaps . Because of these properties III-nitrides electron in Γ-valley is different. The Boltzmann
are used in the blue and UV light emitting diodes equation is solved iteratively for our purpose, jointly
(LED’s) ,blue lasers ,UV detectors and high power , incorporating the effects of all the scattering
high temperature field effect transistors [2,3,4,5,6]. mechanisms. This paper is organized as follow as
Aluminum nitride is a very interesting material follows details of iterative model is presented in
because of it’s wide band gap (6.3 ev), high Section II and result of iterative calculations carried
decomposition temperature (2400 c) chemical out on ZB-AlN and WZ-AlN structures are
stability (in air up to 700 c) and good dielectric interpreted in Section III [3-5].
properties . In the last decade considerable interest
arose in the use of thin films of AlN for various II. SOLVING THE BOLTZMANN
applications , from hard coatings and overcoatings TRANSPORT EQUATION
for magneto- optic media ,to thin films transducers In principle the iterative technique give
and GHz-band surface acoustic wave devices .The exact numerical prediction of electron mobility in
bandgap of AlN is direct in the Wurtzite phase and bulk semiconductors. To calculate mobility, we have
indirect in Zincblende phase .The electronic to solve the Boltzmann equation to get the modified
structure around the Valence band maximum of AlN probability distribution function under the action of a
in the WZ structure around the Valence band steady electric field . Here, we have adopted the
maximum of AlN in the WZ structure is different iterative technique for solving the Boltzmann
from that of the ZB-type crystal. In WZ-AlN ,the transport equation . Under application of a uniform
bandgap is 4.3 ev and direct at gamma point and in electric field the Boltzmann equation can be written
ZB-AlN the conduction-band minimum (CBM) is as :
located away from the gamma point at the X-point
and in this point the bandgap is 3.2 ev. ZB-AlN is an
(1)
object of the invention to prepare ZB-AlN OF
where f=f(k) and f'=f(k' ) are the probability
sufficient quality and thickness to characterize it for
distribution functions and s=s(k,k') and s'=s(k',k) are
its mechanical, optical and electrical properties and
the differential scattering rates . If the electric field is
to be useful for device fabrication . WZ-AlN is a
small ,we can treat the change from the equilibrium
404 | P a g e
2. H. Arabshahi, M. Izadifard and A. Karimi * / International Journal Of Engineering Research
And Applications (IJERA) ISSN: 2248-9622 WWW.IJERA.COM
Vol. 2, issue 5, september- october 2012, pp.404-407
distribution function as a perturbation which is first g(k) is equal zero , we get the relaxation time
order in the electric field. The distribution in the approximation result after the first iteration . We
presence of a sufficiently small field can be written have found that convergence can normally be
quite generally as: achieved after only a few iterations for small electric
f(k)=f0(k) + g(k) cos 𝜃 fields.
(2) Once g(k) has been evaluated to the required
Where f0(k) in the equilibrium distribution accuracy , it is which is given by :
function, θ is the angle between k and E and g(k) is
an isotropic function of k, wich is proportional to the
magnitude of the electric field .Boltzmann transport
equation is involved in scattering mechanisms may (5)
have occurred in the material . In this work we
regarded that it was taken place acoustic phonon
Where d is defined as 1/d =m ∇k E / ℏ2 k. We took the
deformation potential scattering, acoustic
structure of AlN compound as Wurtzite structure
piezoelectric scattering, ionized impurity scattering
and Zincblende structure And we took into account
and polar optic phonon scattering for given
electron screening [2].
materials. We took acoustic phonon deformation
potential scattering, acoustic piezoelectric scattering
,ionized impurity scattering as elastic process ( Sel) III. Results
and also polar optic phonon scattering as inelastic Effective mobility parameters are such as
process (Sinel ).The total elastic scattering rate will be temperature , density , coefficient of nonparabolic
the sum of all the different scattering rates . electron effective mass and the energy balance and
so on .
S(k,k') = Sel(k,k') +Sinel(k,k')
2.6
(3) 2.4 T=500 K
In this case, Sinel represents transitions from 2.2
Total scattering(s )*(10 )
13
the state characterized by k to k' either by emission 2.0
[Sem(k,k')] or by absorption [Sab(k,k')] of a phonon . 1.8
-1
1.6
And polar optic phonon scattering, we have to 1.4
T=300 K
consider scattering – in rates by phonon emission and 1.2
1.0
Parameter WZ- ZB-AlN 0.8
AlN 0.6
ZB-AlN
Band-gap (eV) 6.25 5.4 0.4
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Electron effective mass (m* ) 0.31 0.35 Energy (ev)
Static relative permitivity 0 8.5 8.07
Optical relative permitivity 4.77 4.46 Fig 1. Changes total scattering electron function in
Density (kgm-3 ) 3230 3257 terms of energy in bulk WZ-AlN at the different
Sound velocity (ms-1 ) 9060 5740 temperature.
Deformation potential (eV) 9.5 9
Optical phonon energy (eV) 0.0992 0.099
1.8
absorption . T=500 K
1.6
Total scattering(s )*(10 )
13
Table 1. Important parameters used in our 1.4
-1
calculations for WZ-AlN and ZB-AlN [6-7-9]. 1.2 T=300 K
Using Boltzmann equation and considering 1.0
all differential scattering rates , the factor g(k) in the 0.8
perturbed part of the distribution function f(k) can 0.6
be given by : 0.4 WZ-AlN
0.2
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Energy (ev)
.
Fig 2. Changes total scattering electron function in
(4) terms of energy in bulk ZB-AlN at the different
temperature.
Note the first term in the denominator is simply the Figure 1 and 2 show total scattering
momentum relaxation rate for elastic scattering . It is depends on energy and increasing temperature
interesting to note that if the initial distribution is causes increasing in bulk ZB-AlN and WZ-AlN
chosen to be the equilibrium distribution, for which materials.
405 | P a g e
3. H. Arabshahi, M. Izadifard and A. Karimi * / International Journal Of Engineering Research
And Applications (IJERA) ISSN: 2248-9622 WWW.IJERA.COM
Vol. 2, issue 5, september- october 2012, pp.404-407
effective mass of ZB-AlN is more than WZ-AlN,
with increasing the effective mass , the electron
2.0
mobility decreases with increasing electron effective
1.8 WZ-AlN mass increases the moment of it which reduces the
Total scattering(s )*(10 )
13
1.6 electron acceleration in an electric field is uniform,
which ultimately reduces mobility in an electric field
1.4
-1
is present . Increasing the non parabolic electron
1.2 ZB-AlN energy bands are meant to be paved.
1.0 Smooth energy bands, effective mass of electrons and
thus increase the mobility reduction in the crystal is.
0.8
0.6
0.4
T=300 K 340
0.2 320
T=300 K
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
300
Energy (ev)
Electron mobility (cm /v s)
280 WZ-AlN
2
260
Fig 3. Changes total scattering electron function in 240
220
terms of energy in bulk ZB-Aln and WZ-AlN at
200
different temperature. 180
Figure 3 shows comparison of totals 160
scattering in WZ-AlN and ZB-AlN at the different 140 ZB-AlN
temperature .Our calculation results show that the 120
totals scattering rate in WZ-AlN is more than ZB- 100
0.00E+000 2.00E+018 4.00E+018 6.00E+018 8.00E+018 1.00E+019
AlN . Only a weak electric field the electrons in the -3
electron concentration (cm )
Γ-valley electric transportation involved. Because
they no longer have the energy to go to the valley
.Hence transitions between valley occurs. In weak Fig 5. Changes the electron mobility function in
electric field piezoelectric scattering and ionized terms of electron concentration in bulk ZB-AlN and
impurity scattering play an important role and they WZ-AlN at T=300 K.
can not be ignored. Figure 5 shows the electron mobility of WZ-AlN is
more than ZB-AlN in range of electron concentration
.In this case we see the electron mobility decreases
with increasing the electron concentration. Because
of the increasing number of electrons ionized
2800 impurity centers is also increasing the number of
times that electron feels coulomb potential, therefore
Electron mobility(cm /Vs)
2400
the ionized impurity scattering rate increases. So,
2
2000
WZ-AlN electron mobility decreases.
1600
We result that electron mobility at the definite
temperature 300K for the WZ-AlN semiconductor is
1200 gained about 337.61cm2 v-1s-1 and for ZB-AlN about
800
152.254 and the electron mobility WZ-AlN is more
than ZB-AlN. This increasing is because of small
400 effect mass.
ZB-AlN
0
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4. H. Arabshahi, M. Izadifard and A. Karimi * / International Journal Of Engineering Research
And Applications (IJERA) ISSN: 2248-9622 WWW.IJERA.COM
Vol. 2, issue 5, september- october 2012, pp.404-407
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