lecture 1 electronic devices and control

Electronic devices and control lectures

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2. Lecture 1 Basic Concept Of Semiconductors 2

3. ED&C ? Electronics? E lectron mechanics, which means to study the behavior of an electron under different conditions of applied electric field . The branch of engineering in which the flow and control of electrons in semiconductor are studied is called electronics .   EDC D eals with the design and applications of electronic devices and circuits such as passive components, diodes, triodes and transistors, rectification and power supplies, amplifying circuits, electronic instruments, and oscillators.  3

4. Bohr model 4

5. 5 Hydrogen atom Helium atom

6. Energy increases as the distance From the nucleus increases 6

7. Valence electron: Farther, high energy level, less tightly bound Electrons with highest energy are loosely bound and exist in valence shell. Ionization: loosing valence electron When atom absorbs energy from light or heat, its energy is raised. Valence electron gain energy and jumps to higher orbits within the valence shell. If it acquires sufficient amount of energy, it escapes from the atoms influence, leaving neural atom with the excess of positive charge. Escaped valence electron is called Free Electron. 7

8. Atom consist of valence shell and core Core: consist of inner shells and nucleus. 8 Diagram of a carbon atom

9. Conductors Good conductors have low resistance so electrons flow through them with ease. Best element conductors include: Copper, silver, gold, aluminum, & nickel Alloys are also good conductors: Brass & steel Good conductors can also be liquid: Salt water 9

10. Conductors: Material that easily conducts electric current. Characterized by atoms having single valence electron which is very loosely bound. Loosely bound valence electron can easily break away from their atoms and become free electron. These free electrons, moving in the same direction, make up the current. 10

11. Insulators Insulators have a high resistance so current does not flow in them. Good insulators include: Glass, ceramic, plastics, & wood Most insulators are compounds of several elements. The atoms are tightly bound to one another so electrons are difficult to strip away for current flow. Valence electrons are tightly bound to the atoms. Insulator have very few free electrons. 11

12. Semiconductors Material between conductors and insulators in i ts ability to conduct electric current. Common semiconductors are silicon, germanium and carbon. Semiconductor materials can be Elemental (consisting of a single type of atom) or compound (containing more than one element s to form a compound). 12

13. Semiconductors are at the heart of almost every electronic system in use today, from your washing machine to the space shuttle. Semiconductors are materials that essentially can be conditioned to act as good conductors, or good insulators, or any thing in between. Historically, germanium was one of the first semiconductors to be used but almost replaced by silicon now. 13

14. Compound semiconductors can be formed from combinations of elements from columns III and V or columns II and VI. The compound semiconductor materials gallium arsenide (GaAs) and indium phosphide ( InP ) are the most important material for optoelectronic applications, including light-emitting diodes (LEDs), lasers, and photodetectors. Many organic compounds, e. g. polyacetylene (CH) n , are semiconductors. Some semiconductors exhibit magnetic or ferroelectric behavior, Others become superconductors when doped with sufficient carriers 14

15. Crystal structure of silicon

16. The Energy bands In any material, there are 2 energy band: 1. Valence band : the outermost shell that determines the conductivity 2. Conduction band : the band outside the valence shell. The 2 bands are separated by one energy gap called – forbidden gap . The valence band contains with electrons. The electrons can move to the conduction band if it have enough energy ( eg : light or heat). When the electron absorbs enough energy to jump from valence band to the conduction band, the electron is said to be in excited State and it moves freely throughout the material. 17

17. The concept of energy bands is particularly important in classifying materials as conductors, semiconductors, and insulators. 18

18. Semiconductor : has a smaller forbidden band and requires less energy to move an electron from the valence band to the conduction band . • Therefore, for a certain amount of applied voltage, more current will flow in the semiconductor than in the insulator.

19. semiconducting elements : – low electrical conductivity at room temperature – Electrical conductivity increases with temp. Gap between valence and conduction band is intermediate in size. Semiconducting elements form the basis of solid state electronic devices . Metalloids (such as silicon or germanium) are semiconducting elements whose electrical conductivity increases as temperature increases . A striking property of these elements is that their conductivities increase markedly when they are doped with small quantities of other elements. 20

20. semiconducting elements : Made from materials that have four valence electrons in their outer orbitals. Germanium and silicon are the most common. A pure semiconductor material such as silicon or germanium has no special properties and will make a poor conductive material . Why Silicon is preferred over germanium? (Home work) 21

21. Comparison of semiconductor an conductor 22

22. Silicon and germanium 23 Widely used in diode transistors, ICs.

23. Thank you 24