CONDUCTION IN SEMICONDUCTORS
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At room temperature of 300°K, it requires an energy of EG = 1.12 eV to break covalent bonds in Silicon material and EG = 0.7 eV to break the covalent bonds in Germanium material and to produce some ‘electron–Hole pairs’. Even at room temperature, a few of the covalent bonds will be broken, leading to equal number of electrons and Holes in Conduction Band and Valence Band, respectively. Electrons...
CONDUCTIVITY AND RESISTIVITY OF SEMICONDUCTOR MATERIALS
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The value of conductivity of a material gives us an estimate of the extent to which a material supports the flow of current through it. Electrical conductivity depends upon the number of electrons available in the conduction process. The concept of conductivity is useful in many engineering applications including medical electronics. J = nqμE Equation (2.17) derived in the previous section...
CURRENT DENSITY IN A CONDUCTING MEDIUM
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Currents in metals are due to the movement of charge carriers ‘electrons’. where I is the current in Amperes and A is the cross-sectional area of conducting medium in metre2. Describing current density J as current per unit area has the advantage, since the dimensions of the conducting medium are not directly involved. Relation between current density and charge density ρ is described...
CONDUCTION IN CONDUCTORS AND SEMICONDUCTORS
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Conduction in conductors and semiconductors Mobility μ: In good conductors like metals, free electrons exist in abundance. They are supposed to be accelerated under the influence of electric or magnetic field as per ballistic (dynamics) laws. But in practice it is found that the electrons move with a constant velocity proportional to the field. The reason for this is the random nature of the...
CONDUCTION (INVERSE OF RESISTANCE) IN INTRINSIC SEMICONDUCTORS
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Purest semiconductor is known as intrinsic semiconductor. At 0°K, semiconductor behaves like an insulator, because energies of the order of EG cannot be acquired from an electric field. At room temperature, covalent bonds in the semiconductor may be broken into a few Hole–electron pairs, contributing to current flow through the material allowing the conductivityto increase. With respect to...
CLASSIFICATION OF MATERIALS
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When voltages are applied, materials offer different values of electrical resistances to the passage of currents through them. On the basis of electrical resistances, materials are classified as conductors, semiconductors and insulators. In solids, available energy states for the electrons form ‘bands of energy levels’ instead of discrete energy levels in atoms. Conductors: Materials with adjacent...
ENERGY-BAND CONCEPTS OF MATERIALS
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Energy-band Concepts of Materials The electron energy levels for a single free atom in a gaseous medium are discrete, since the atoms are sufficiently far apart. So the energy levels of individual atoms are not perturbed. The proximity of neighbouring atoms in solid media such as crystals does not appreciably affect the energy levels of inner shell electrons. But, groups of energy levels of...
ELECTRONIC CONFIGURATION OF A GERMANIUM ATOM
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Fig. 2.3 Electron configuration of germanium atom Germanium semiconductor atom has ‘atomic number’ Z = 32. It has 32 positive charges in the nucleus and 32 electrons in various shells containing 2, 8, 18 and 4 electrons. Germanium atom is electrically neutral. Germanium semiconductor as a whole is electrically neutral. First, second and third orbits are completely filled. Fourth orbit...
ELECTRON CONFIGURATIONS OF SILICON AND GERMANIUM ATOMS
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REVIEW OF SEMICONDUCTOR PHYSICS The electronics subject begins from the concepts of behaviour of charge carriers in electron devices and Integrated Circuits (ICs) under influence of electric fields. A model of an atom is shown in Fig. 2.1. The aspect of electron motion is analogous to the planetary motion in which the planets rotate round the sun. On similar lines, electrons move in closed...
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