Tài liệu Introduction to Semiconductors & Diodes pdf

Introduction to Semiconductors & Diodes EE106 Analogue Electronics Supplementary Notes F. O’Malley April 2005 Semiconductor Diodes • A diode is a very useful non-linear device • It allows current to flow in one direction and prevents it flowing in the other Cathode Anode I Diode Operation • When a positive voltage is applied across the diode then current will flow • The diode is said to be forward biased • When a negative voltage is applied then the diode is reverse biased and no current will flow Diode Characteristic Curve Forward Biased Diode • A positive voltage is applied to circuit so current will flow • Diode effectively behaves like a short circuit when forward biased 1k Ω i + 10V - + v o - Reverse Biased Diode 1k Ω i - 10V + + v o - • A negative voltage is applied to circuit so NO current will flow • Diode effectively behaves like an open circuit when reverse biased • Two common types of semi-conductive materials are silicon and germanium – both have four valance electrons • When silicon and germanium atoms combine into molecules to form a solid material, they arrange themselves in a fixed pattern called a crystal – atoms within the crystal structure are held together by covalent bonds (atoms share valence electrons) • An intrinsic crystal is one that has no impurities Introduction to Semiconductors Atomic Structure of Semiconductors Atomic Bonding in Silicon Energy Band Diagrams Comparison [...]... Conduction in Semiconductors - Doping • In an intrinsic semiconductor, there are relatively few free electrons – pure semi-conductive materials are neither good conductors nor good insulators • Intrinsic semi-conductive materials must be modified by increasing the free electrons and holes to increase its conductivity and make it useful for electronic devices • Doping is the process of adding impurities to intrinsic... source is connected to the p region, and the positive terminal is connected to the n region • If the external reverse-bias voltage is increased to a large enough value, reverse breakdown occurs – minority conduction-band electrons acquire enough energy from the external source to accelerate toward the positive end of the diode, colliding with atoms and knocking valence electrons into the conduction band... materials to increase and control conductivity within the material – by adding impurities, n-type and p-type extrinsic semiconductive material can be produced n-Type Semiconductors • n-type material is formed by adding pentavalent (5 valence electrons) impurity atoms – electrons are called majority carriers in n-type material – holes are called minority carriers in n-type material p-Type Semiconductors. .. Applications • Due to this characteristic diodes find many useful applications – Power supplies, voltage regulators – Tuning devices in RF (radio frequency) tuned circuits, frequency multiplying devices in RF circuits, mixing devices in RF circuits, – switching applications – logic decisions in digital circuits – There are also diodes which emit "light", of course these are known as light-emitting -diodes or... electron jumps to the conduction band, a vacancy is left in the valence band within the crystal (called a hole) – called an electron-hole pair • Recombination occurs when a conduction-band electron loses energy and falls back into a hole in the valence band Electron – Hole Pairs Free Electron Drift Electron Current • Application of a voltage causes thermally generated free electrons to move towards +ive... Forward bias is the condition that permits current through a diode – the negative terminal of the VBIAS source is connected to the n region, and the positive terminal is connected to the p region Barrier Potential • The barrier potential, VB, is the amount of voltage required to move electrons through the electric field – At 25°C, it is approximately 0.7 V for silicon and 0.3 V for germanium – As the... terminal of the bias-voltage source pushes the conduction-band electrons in the n region toward the pn junction, while the positive terminal pushes the holes in the p region toward the pn junction • When it overcomes the barrier potential (V B), the external voltage source provides the n region electrons with enough energy to penetrate the depletion region and move through the junction Reverse Bias • Reverse... circuits – There are also diodes which emit "light", of course these are known as light-emitting -diodes or LED's Diode Symbols • Various diodes symbols are shown Diode Packages Rectification • Process of converting a AC signal to a DC signal • The first step is to use a diode circuit as shown Half-Wave Rectifier +ive half• Observe performance of diode during two half cycle cycles • During +ive half... called majority carriers in n-type material – holes are called minority carriers in n-type material p-Type Semiconductors • p-type material is formed by adding trivalent (3 valence electrons) impurity atoms – holes are called majority carriers in p-type material – electrons are called minority carriers in p-type material Forming a Diode • Diode is formed from manufacturing p and n type material side . Introduction to Semiconductors & Diodes EE106 Analogue Electronics Supplementary Notes F. O’Malley April 2005 Semiconductor Diodes • A. held together by covalent bonds (atoms share valence electrons) • An intrinsic crystal is one that has no impurities Introduction to Semiconductors Atomic