ELECTROICS DEVICES LAB Conductor Insulator Desired DIODE ■ A diode is a two terminal device which conducts current more easily in one direction than in the opposite direction. ■ The diode is a commonly used device in electrical and electronic engineering. ■ In today's Lecture, we will discuss its: 1. structure (construction) 2. working principle. 3. Applications ■ Semiconductors are materials that have electrical conductivity in between conductors and insulators. ■ The most common semiconductors are Germanium and Silicon. ■ In its naturally occurring form, they are called intrinsic semiconductors. But an intrinsic semiconductor (a semiconductor in its natural form) is not suitable for making any electronic device. ■ One primary reason for this is very low electrical conductivity of an intrinsic semiconductor at room temperature. Researchers had found a way to manipulate the pure semiconductor properties and thereby improve its electrical conductivity several times. ■ This is achieved by a process named doping (by adding a small amount of impurity to Silicon and Germanium). The newly formed semiconductor (known as doped semiconductor) is called an Extrinsic semiconductor. There are 2 types of extrinsic semiconductor: 1) p-type semiconductor 2) n-type semiconductor. ■ A p-type semiconductor is formed by doping Germanium (Ge) or Silicon (Si) with a trivalent (number of valence electrons=3) element like Indium, Boron or Aluminum. ■ An n-type semiconductor is formed by doping Ge or Si with a pentavalent (number of valence electrons=5) element like Arsenic or Antimony. ■ n-type semiconductor will have an excess of electrons or negative charge carriers(surplus of electrons that can be donated to other elements) ■ p-type semiconductor will have a surplus of holes or positive charge carriers (you must understand that in reality a hole or a positive charge is representation of “absence of an electron” ). semiconductor). Formation of Depletion Layer Biasing the Diode The process of applying an external voltage is called as “biasing”. There are two ways in which we can bias a pn junction diode. 1) Forward bias 2) Reverse bias Appearance of real component Schematic symbol Putting “R” in series with Diode : Why? Forward Characteristics Curve for a Junction Diode Reverse Characteristics Curve for a Junction Diode PN junction diode I-V characteristics Standard numbering system standard used for semiconductor devices. 1N4007 ■ 1N indicates single junction semiconductor. ■ 4007 is the specific number to indicate the particular diode.