MODULE 1 ELECTRONICS - is the technology based on the behavior, properties, and control of electrons - is distinct from electrical science - is the branch of physics, engineering, and technology dealing with electrical circuits that involve active electrical components such as vacuum tubes, transistors, diodes, and integrated circuits, and associated passive interconnection technologies. ELECTRONICS ENGINEERING - deals with the study of small-scale electronic systems including computers and integrated circuits - an engineering discipline where non-linear, active electrical components, and semiconductor devices are utilized to design electronics circuits, devices, and systems. - deals with the implementation of applications, principles and algorithms developed within many related fields ELECTRICAL ENGINEERING - is considered to deal with the problems associated with large-scale electrical systems such as power transmission and motor control. ELECTRONIC COMPONENTS - is a basic electronic element that is available in a discrete form that has two or more electrical terminals Classification of Electronic Components: ● Passive Devices - these are components incapable of controlling current by means of another electrical signal Examples: resistors, capacitors, inductors, transformers, diodes ● Active Devices - are any type of circuit component with the ability to electrically control electron flow (electricity controlling electricity) - some active devices allow a voltage to control this current while other active devices allow another current to do the job. - devices utilizing a static voltage as the controlling signal are called voltage-controlled devices - devices working on the principle of one current controlling another current are known as current-controlled devices. Examples: vacuum tubes, transistors, silicon-controlled rectifiers (SCRs), and TRIACs COMMON ELECTRONIC SYMBOLS ATOM - derived from the Greek word “atomos”, meaning “indivisible” - is the tiny basic building block of all matters ATOMIC MODELS ● Thomson Model ● - also known as “Plum-Pudding Model”; proposed by Sir Joseph John Thomson - J.J Thomson considered that the structure of an atom is something like a raisin bread, so that his atomic model is sometimes called the raisin bread model. He also assumed that the basic body of an atom is a spherical object containing electrons confined in homogeneous jellylike but relatively massive positive charge distribution. Rutherford Model - also known as “Planetary Model”; proposed by Ernest Rutherford in 1911 - a model in which the electric charge in an atom is not distributed over the whole area of the atom but concentrates in a small area called nucleus. - describes the atom as having a central positive nucleus surrounded by negative orbiting electrons. - this model suggested that most of the mass of the atom was contained in the small nucleus, and that the rest of the atom was mostly empty space. ● Bohr Model levels are the first, second, etc., excited states - electrons can jump up or down between energy levels, but cannot have energy values between the allowed energy levels. PARTICLES OF ATOM ● Electrons - discovered by Sir Joseph John Thomson in April 30, 1897 - extremely small and light particles that carry negative electric charge −19 ● - proposed by Neils Bohr in 1913 - a quantum–physics–based modification of the Rutherford model; each orbit has a corresponding amount of energy - depicts an atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus– similar in structure to the solar system, but with electrostatic forces providing attraction, rather than gravity. - energy levels are quantized; only specific discrete energy levels are possible; as long as the electrons are in one of these quantized energy levels or stationary states, they orbit the nucleus and remain stable without emitting electromagnetic radiation and losing energy. - when electrons orbit the nucleus in more distant orbits, they have more total energy - the lowest energy level is the ground state and higher energy (− 1. 6022 𝑥 10 𝐶𝑜𝑢𝑙𝑜𝑚𝑏𝑠) Proton - discovered by Ernest Rutherford in 1919 - carries positive electric charge −19 ● (1. 6022 𝑥 10 𝐶𝑜𝑢𝑙𝑜𝑚𝑏𝑠) Neutron - discovered by Sir James Chadwick in 1932 - has a mass approximately equal (slightly heavier) to that of a proton but has no electric charge ATOMIC NUMBER - equal to the number of protons in the nucleus, which is the same as the number of electrons in an electrically balanced (neutral) atom ATOMIC MASS - equal to the sum of the number of protons and neutrons of an atom - each orbital shell must be filled with a 2 maximum number of 2𝑛 electrons VALENCE ELECTRONS - loose electrons found in the outermost orbit of an atom - indicate how easily the atom can gain or lose electrons CLASSIFICATION OF MATERIALS ACCORDING TO CONDUCTIVITY 1. Conductor - a substance, body, or material which has more electrons that are free to move - Free electron (the released electron dislodged from its original shell due to absorption of energy) - Hole (the term used to refer the vacancy left by free electron when it departs from its original shell; it usually behaves like a positive charge since it can attract and capture electron in the immediate vicinity) 2. Insulator - a substance, body or material which has a characteristic that is extremely opposite to conductor with more than 4 valence electrons but ideally, it has 8 valence electrons - Bound Electrons (the term for 8 valence electrons because they are tightly held by the atoms) 3. Semiconductor - a substance, body, or material which has a characteristic in between a conductor and insulator; has 4 valence electrons - it can be made to act as a conductor at one time and as an insulator at another depending upon the manipulation with its inherent nature. - a semiconductor in its pure (intrinsic) state is neither a good conductor nor a good insulator ENERGY LEVELS - the farther the electron is from the nucleus, the higher is the energy state, and any electron that has left its parent atom has a higher energy state than any electron in the atomic structure. ENERGY GAP - is the energy difference between the conduction band and valence band - is the energy required to move or transfer a valence electron at the valence band to the conduction band SEMICONDUCTOR MATERIALS - are insulators at absolute zero temperature and conduct electricity in a limited way at room temperature - have exactly the 4 valence electrons - it can be doped with impurities that alter its electronic properties in a controllable way - atoms in a semiconductor material are arranged in the form of crystal lattice - each atom shares its 4 valence electrons with 4 neighboring atoms - the sharing of electrons creates a bind that holds the atoms together; this electron-pair bond is commonly referred to as covalent bond - the most common single–element or elemental semiconductors are silicon, germanium, and carbon. Compound semiconductors such as gallium arsenide are also commonly used. SILICON (Si) - it is a non-metallic element which was discovered in 1823 and found extensively in the earth’s crust GERMANIUM (Ge) - is a brittle, grayish-white element discovered in 1886 earth - may be recovered from the ash of certain types of coals in the form of germanium dioxide powder GALLIUM ARSENIDE (GaAs) - works better than silicon in several ways - though it needs more voltage to operate but will function at higher frequencies because the charge carriers move faster - GaAs devices are relatively immune to the effects of ionizing radiation such as X-rays and Gamma rays - it is used in light-emitting diodes, infrared-emitting diodes, laser diodes, visible-light and infrared detectors, UHF amplifying devices, and a variety of integrated circuits TYPES OF SEMICONDUCTOR MATERIALS 1. Intrinsic Semiconductor - refers to pure materials and therefore free from impurities that exist naturally like pure silicon and pure germanium - has equal numbers of negative carriers (electrons) and positive carriers (holes) - if a voltage is applied, then both the electron and the hole can contribute to a small current flow 2. Extrinsic Semiconductor - refers to semiconductor materials doped with some impurities so as to alter their original electrical properties, normally to increase their electrical conductivities DOPING - is the process of adding pentavalent or trivalent impurities (dopants) to an intrinsic material in order to increase the conductivity of the semiconductor material ● Lightly Doped – only few impurities are added resulting to a higher resistance (lower conductivity) ● Heavily Doped – more impurities are added resulting to a lower resistance (higher conductivity) TYPES OF IMPURITIES 1. Pentavalent Atom (Donor Impurity) - atom with 5 valence electrons - adding such substance causes conduction mainly by means of electron flow - the excess electrons are passed from atom to atom when a voltage exists across the material Examples: Antimony (Sb), Arsenic (As), Bismuth (Bi), Phosphorus (P) 2. Trivalent Atom (Acceptor Impurity) - atom with 3 valence electrons - adding such substance causes conduction by means of hole flow Examples: Boron (B), Gallium (Ga), Indium (In), Aluminum (Al) TYPES OF EXTRINSIC SEMICONDUCTOR MATERIAL 1. N-type Material - is the result of adding donor impurities - majority carriers are electrons - minority carriers are holes 2. P-type Material - is the result of adding acceptor impurities - majority carriers are holes - minority carriers are electrons ELECTRON CURRENT - when a voltage is applied across a piece of intrinsic semiconductor, the thermally generated free electrons in the conduction band, which are free to move randomly in the crystal structure, are now easily attracted towards the positive end. HOLE CURRENT - occurs in the valence band, where the holes created by the free electrons exist - electrons remaining in the valence band are still attached to their atoms and are not free to move randomly in the crystal as are the free electrons. However, valence electrons can move into a nearby hole with little change in its energy level, thus leaving another hole where it came from. - Effectively, the hole has moved from one place to another in the crystal structure. CURRENT DENSITY (J) - is the electric current per unit area SEMICONDUCTOR PARAMETERS DRIFT VELOCITY - is the rate at which an electron, under the influence of an electric field, travels at a certain distance at a certain time. ELECTRON CONCENTRATION (η) - is the number of electrons per unit volume VOLUME CHARGE DENSITY (ρ𝑣) - is the measure of electric charge per unit volume CONDUCTIVITY OR SPECIFIC CONDUCTANCE (σ) - is the material’s ability to conduct an electric current CURRENT - is the total charge passing through any area per unit time CURRENT DENSITY conductivity) (in terms of RESISTIVITY OR SPECIFIC RESISTANCE (ρ) - is the measurement of how strong a material opposes the flow of electric current MASS ACTION LAW - under thermal equilibrium, the product of the free negative and positive concentration is a constant independent of the amount of impurity doping. RESISTANCE - is the opposition to the passage of an electric current through that element INTRINSIC CONCENTRATION Function of Temperature) (as a OHM’S LAW - states that the current through a conductor between two points is directly proportional to the potential difference across two points INTRINSIC CONCENTRATION (as a Function of Effective Density of States) CONVERSION OF UNITS 𝑐𝑜𝑢𝑙𝑜𝑚𝑏 𝑠𝑒𝑐 𝑣𝑜𝑙𝑡 𝑂ℎ𝑚 ● 1 Ampere = 1 ● 1 Ampere = 1 ● ● ● 1 Joule = 1 Volt-Ampere-sec 1 Joule = 1 Watt-sec 1 Watt = 1 Volt-Ampere ● 1 Volt = 1 ● 1 𝑗𝑜𝑢𝑙𝑒 𝑐𝑜𝑢𝑙𝑜𝑚𝑏 𝑉𝑜𝑙𝑡−𝑠𝑒𝑐 Coulomb = 1 𝑂ℎ𝑚 LAW OF ELECTRICAL NEUTRALITY states that the total positive charge is equal to the total negative charge Cases: - - EINSTEIN RELATIONSHIP - mobility characterizes how quickly an electron or hole can move through a semiconductor, when an electric field is applied to it. - the process of electrons or holes moving from the higher concentration region to the lower concentration region is called diffusion. the drift current density of electrons or holes is directly proportional to the mobility of electrons or holes while the diffusion current density of electrons or holes is directly proportional to the diffusion coefficient of electrons or holes the equation which relates the mobility µ (of electrons or holes) and the diffusion coefficient (of electrons Dn or holes Dp) is known as Einstein Relationship. SAMPLE PROBLEMS 1. A n-type Silicon sample is 3 mm long and has a rectangular cross-section, 50µ𝑚 by 100µ𝑚. The donor concentration at 300 K 14 2. If a donor impurity is added to the 8 extent of one part in 10 Ge atoms, find its resistivity. 3 is 5 𝑥 10 /𝑐𝑚 and corresponds to 8 one impurity atom for 10 Si atoms. A steady current of 1µ𝐴 exists in the bar. Determine the electron and hole concentrations, the conductivity, and the voltage across the bar. 3. What is the intrinsic concentration of Ge crystal at 500K?
