Electrical Properties PDF

Electrical Exploring the electrical properties Properties of materials  01 Describe the four possible electron band structures for solid materials. 02 Briefly describe electron excitation ev...

Electrical Exploring the electrical properties Properties of materials  01 Describe the four possible electron band structures for solid materials. 02 Briefly describe electron excitation events that produce Learning free electrons/holes in metals, semiconductors and insulators. Objectives 03 Distinguish between intrinsic and extrinsic semiconducting materials. 04 Name and describe the three types of polarization. 05 Briefly describe the phenomena of ferroelectricity and piezoelectricity. Electrical Conduction OHM’S LAW RESISTIVITY The most important electrical A material property that is independent of characteristics of a solid material sample size and geometry where: where: p - electrical resistivity V - voltage I - length of the material I - current R - resistant R - resistant A- area of cross- section CONDUCTIVITY Is used to specify the electrical character of a material where: σ- electrical conductivity ρ- electrical resistivity  ELECTRONIC AND IONIC CONDUCTION Electronic conduction Ionic Conduction The movement of electrons from The movement of ions from one one place to another. (copper place to another. (Salt water, wires, silicon transistors, and batteries, and solid oxide fuel organic light-emitting diodes) cells) ENERGY BAND Four different types of band structures Fermi energy STRUCTURES IN the energy difference between the highest and lowest occupied single-particle states in a SOLIDS quantum system of non-interacting fermions at absolute zero temperature. valence band Hence, the electron orbitals overlap the outermost electron orbital of an atom of when atoms come together. In solids, any specific material that electrons actually several bands of energy levels are occupy. formed due to the intermixing of atoms conduction band in solids. We call these set of energy the band of electron orbitals that electrons can levels as energy bands. jump up into from the valence band when excited. When the electrons are in these orbitals, they have enough energy to move freely in the material. energy band gap an energy range in a solid where no electronic states exist. CONDUCTION IN TERMS OF BAND AND ATOMIC BONDING MODELS Free electrons (negatively charged) electrons that are in random continuous motion and participate in the conduction process Hole (positively charged) found in semiconductors and insulators  Metals all the valence electrons have freedom of motion and form an electron gas that is uniformly distributed throughout the lattice of ion cores. CONDUCTION IN Insulators and Semiconductors TERMS OF BAND AND empty states adjacent to the top of the ATOMIC BONDING filled valence band are not available. To become free, therefore, electrons must MODELS be promoted across the energy band gap and into empty states at the bottom of the conduction band. ELECTRON MOBILITY When a conductor is connected to a voltage source, an electric field is applied. As a result, a force is brought to bear on the free electrons; as a consequence, they all experience an acceleration in a direction opposite to that of the field, by virtue of their negative charge.  ELECTRICAL RESISTIVITY OF INFLUENCE OF IMPURITIES METALS The presence of impurities in a metal disrupts the regular lattice structure, scattering electrons. Therefore, the INFLUENCE OF TEMPERATURE electrical resistivity increases impurities As temperature increases, the thermal in a conductor increase. vibrations of atoms in the metal lattice intensify. This increased vibration hinders INFLUENCE OF PLASTIC DEFORMATION the free movement of electrons, leading to Plastic deformation also raises the higher resistivity. electrical resistivity as a result of increased numbers of electron-scattering dislocations. Furthermore, its influence is much weaker than that of increasing temperature or the presence of Where: impurities. Pt- thermal Resistivity a & p0 - Constants for each metal T - Temperature  INTRINSIC SEMICONDUCTION A pure material whose electrical behavior is determined by its inherent electronic structure, without any influence from impurities. Semiconductivity EXTRINSIC SEMICONDUCTION One in which the electrical properties are significantly influenced by the presence of impurity atoms introduced into the material. These impurities modify the material's conductivity.  INTRINSIC SEMICONDUCTION Concept of a Hole and Electron Hole is an electric charge carrier with a positive charge (+1.6 x 10⁻¹⁹ C) , equal in magnitude but opposite in polarity to the charge on the electron  EXTRINSIC SEMICONDUCTION n-Type The primary charge carriers are electrons. Electrons are majority carriers by virtue of their density or concentration Holes are the minority charge carriers The Fermi level is shifted upward in the energy band gap, closer to the donor states. Its exact position depends on temperature and donor concentration. A donor state is an energy level near the conduction band introduced by impurities, providing free electrons.  EXTRINSIC SEMICONDUCTION p-Type Formed by doping the material with acceptor impurities. Holes are majority carriers due to high concentration Electrons are the minority charge carriers The Fermi level is located within the band gap, closer to the acceptor state near the top of the valence band. Doping is the process of intentionally adding impurity atoms to a pure semiconductor to alter its electrical properties. An acceptor state is an energy level introduced near the valence band when acceptor impurities are added. THE TEMPERATURE DEPENDENCE OF CARRIER CONCENTRATION Intrinsic Semiconductor Carrier concentration increases with temperature due to thermal excitation across the band gap. Ge has higher concentration than Si because of its smaller band gap (0.67 eV vs. 1.11 eV). Extrinsic Semiconductor Behavior depends on temperature and doping. Three Regions: Freeze-Out Region (Low T): Insufficient thermal energy to ionize dopants. Extrinsic Region (Intermediate T): Carrier concentration stable, dominated by dopant levels. Intrinsic Region (High T): Intrinsic excitations dominate over dopant contributions. Carrier concentration depends on band gap, temperature, and impurity doping, with distinct behaviors in different temperature regions.  FACTORS THAT AFFECT CARRIER MOBILITY Carrier Mobility Refers to the ease with which electrons and holes move through the semiconductor. Influences conductivity and resistivity. Factors Affecting Mobility Dopant Content: At concentrations < 10²⁰ m⁻³, mobility is maximized and independent of doping. At higher concentrations, both electron and hole mobilities decrease due to impurity scattering. Electrons have higher mobility than holes. Temperature: As temperature increases, both electron and hole mobilities decrease due to enhanced thermal scattering. For concentrations < 10²⁰ m⁻³, mobility- temperature dependence is similar for both carriers. At higher concentrations (> 10²⁰ m⁻³), mobility decreases with increasing dopant concentration and temperature.  THE HALL EFFECT The Hall effect occurs when a magnetic field is applied perpendicular to the direction of current flow in a material, causing a voltage to develop perpendicular to both the current and magnetic field. Used to determine the majority charge carrier type, carrier concentration, and carrier mobility in materials. Rₕ Iₓ - Hall coefficient - Current Bz - Magnetic field d - Specimen Thickness Hall Effect measurements provide insights into charge carrier characteristics, crucial for semiconductor material analysis. SEMICONDUCTOR DEVICES The p–n p–n Junction A diode made from a single Rectifying semiconductor piece, with n-type (negative) on one side and p-type Junction (positive) on the other. Forward Bias Holes from the p-side and electrons from the n-side move toward the junction. Reverse Bias Electrons and holes are drawn away from the junction. Allows current to flow in one The junction becomes highly insulative, direction, acting as a rectifier allowing little to no current flow. (AC to DC conversion). SEMICONDUCTOR DEVICES TYPES OF TRANSISTOR The Transistor Junction Transistor Can amplify electrical signals and act as a switch. Composed of two p-n junctions arranged as p-n-p or n-p-n. The emitter-base junction is forward biased, allowing charge carriers (holes or electrons) to inject into the base. The base-collector junction is reverse biased, leading to amplification of the current. A small increase in input voltage leads to a significant increase in current through the collector. Used in signal amplification (e.g., radios, audio equipment). SEMICONDUCTOR DEVICES TYPES OF TRANSISTOR The Transistor MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) Consists of a substrate of n-type silicon with p-type islands and a gate on top of an insulating layer. The gate modulates the conductivity of the channel between the source and drain. A small voltage at the gate controls a larger current flow between source and drain. Often used in circuits where the signal sources cannot sustain large currents (e.g., in computers and low-power devices). SEMICONDUCTOR DEVICES Application SEMICONDUCTORS IN COMPUTERS Transistors and diodes act as switches in digital circuits. These switches enable arithmetic, FLASH (SOLID-STATE DRIVE) MEMORY logical operations, and Flash Memory is non-volatile, information storage in computers. meaning no power is needed to retain information. It has no moving parts, offering durability and portability. Used in digital cameras, laptops, mobile phones, and USB drives. Capable of withstanding temperature extremes and water immersion.  ELECTRICAL CONDUCTION IN IONIC CERAMICS AND IN POLYMERS Conduction in Ionic Materials Conducting Polymers In ionic materials, conduction results Polymers like polyacetylene and from the migration of both cations and polyaniline have electrical anions when an electric field is conductivities similar to metals. applied. Conductivity arises from delocalized The total conductivity of ionic electrons in alternating single and materials is the sum of electronic and double bonds. ionic conductivity contributions. Doping with impurities like iodine or The ionic conductivity increases with AsF₅ makes them conductive (n-type temperature due to the mobility of or p-type). ions, which depends on their valence These polymers are used in and diffusion coefficient. applications such as batteries, fuel Despite the contributions from both cells, aerospace wiring, and electronic electronic and ionic components, devices. most ionic materials remain insulative, even at elevated temperatures. Dielectric Behavior A dielectric material is electrically insulating (nonmetallic) and exhibits or may be made to exhibit an electric dipole structure. CAPACITANCE The foundation of compact capacitors and advanced memory devices, showcasing unique spontaneous polarization properties. Factors Affecting Capacitance: Plate area, distance between plates, and dielectric constant. Units: Farads (F) Applications: Capacitors in electronic circuits, and energy storage devices. Permittivity and Dielectric Constant Field Vectors and Polarization Permittivity: Measure a material's Electric Field: Force experienced ability to store electrical energy by a unit charge. in an electric field. Electric Displacement: Measure of Dielectric Constant: Ratio of the the electric field in a dielectric permittivity of a material to the material. permittivity of free space. Polarization: The process of Role in Capacitors: High aligning dipoles in a material under dielectric constant materials can the influence of an electric field. increase capacitance. Types of Polarization: Electronic, Applications: Dielectric materials ionic, and orientation. in capacitors, insulators, and electronic components.  TYPES OF POLARIZATION Electronic Polarization Electronic polarization may be induced to one degree or another in all atoms. It results from a displacement of the center of the negatively charged electron cloud relative to the positive nucleus of an atom by the electric field. This polarization type is found in all dielectric materials and exists only while an electric field is present.  TYPES OF POLARIZATION Ionic Polarization Ionic polarization occurs only in materials that are ionic. An applied field acts to displace cations in one direction and anions in the opposite direction, which gives rise to a net dipole moment.  TYPES OF POLARIZATION Orientation Polarization Is found only in substances that possess permanent dipole moments. Polarization results from a rotation of the permanent moments into the direction of the applied field. This alignment tendency is counteracted by the thermal vibrations of the atoms, such that polarization decreases with increasing temperature.  FREQUENCY DEPENDENCE OF THE DIELECTRIC CONSTANT Dielectric Constant and Frequency Dielectric Breakdown As the frequency of the When a dielectric material applied electric field is subjected to a very high increases, the ability of the electric field, a dipoles to reorient phenomenon known as themselves decreases. This dielectric breakdown can results in a decrease in the occur. This happens when a dielectric constant. large number of electrons are excited to the conduction band, leading to a significant increase in current flow through the material.  FREQUENCY DEPENDENCE OF THE DIELECTRIC CONSTANT Dielectric Materials Substances that are poor conductors of electricity but excellent insulators. They play a crucial role in various electronic components, particularly capacitors. Types of Dielectric Materials: Ceramics: High dielectric constants (e.g., barium titanate) Excellent mechanical strength and stability Used in capacitors, insulators, and electronic components Polymers: Lower dielectric constants compared to ceramics Good electrical insulation properties Used in wire insulation, cable insulation, and capacitors OTHER ELECTRICAL CHARACTERISTICS OF Ferroelectrics are dielectric materials that MATERIALS exhibit spontaneous polarization (polarization FERROELECTRICITY without an external electric field). Analogous to ferromagnetism in magnetic materials. When barium titanate heated above 120°C (250°F), the structure becomes cubic, ions align symmetrically, and ferroelectric behavior disappears. Extremely High Dielectric Constants Enables compact capacitors for various applications. Other materials; Rochelle salt, potassium dihydrogen phosphate, potassium niobate, and The foundation of compact capacitors lead zirconate–titanate. and advanced memory devices, showcasing unique spontaneous Capacitors with high efficiency and Memory polarization properties. devices and sensors. OTHER ELECTRICAL CHARACTERISTICS OF Electric polarization induced by mechanical MATERIALS strain or vice versa PIEZOELECTRICITY Found in materials with complex crystal structures and low symmetry. Piezoelectricity in polycrystalline materials can be enhanced through thermal and electrical treatments (heating above the Curie temperature and cooling in a strong electric field). Common piezoelectric ceramics; Barium titanate, Lead zirconate, Lead zirconate– titanate, Potassium niobate (KNbO3) Airbag sensors, seat-belt buzzers, keyless door entry, Microphones, speakers, ink-jet Crucial for converting mechanical and printer heads, strain gauges, Insulin electrical energy, enabling diverse applications such as sonar, sensors, pumps, ultrasonic therapy, cataract actuators, and medical devices removal devices THANK YOU!