“SEMICONDUCTORS”

1. “SEMICONDUCTORS”

2. OBJECTIVES Identifytheimportance of semiconductors. Differentiatesemicondutorsfromconductors and insulators. 3. Identfiy and describe theelementsthatworks as semiconductors. Appreciatetheimportance of semicondutorstomoderntechnology.

4. VACUUM TUBES Vacuumtubeisconsidered as thebackbone of electronicequipment. WHAT IS a VACUUM TUBE ???!

5. VACUUM TUBE In electronics, a vacuumtube, electrontube (in North America), thermionic valve, tube, orvalveis a devicecontrollingelectric current through a vacuum in a sealed container. The container is often thin transparent glass in a roughly cylindrical shape.

6. VACUUM TUBE The simplest vacuum tube, the diode, is essentially an incandescent light bulb with an extra electrode inside.  Vacuum tubes are thus used for rectification, amplification, switching, or similar processing or creation of electrical signals.

8. WHAT IS A SEMICONDUCTOR? A semiconductor is a material which has electrical conductivity between that of a conductor such as copper and an insulator such as glass. The conductivity of a semiconductor increases with increasing temperature, behaviour opposite to that of a metal

9. Current conduction in a semiconductor occurs via free electrons and "holes", collectively known as charge carriers. Adding impurity atoms to a semiconducting material, known as "doping", greatly increases the number of charge carriers within it.

10. DOPING When a doped semiconductor contains excess holes it is called "p-type", and when it contains excess free electrons it is known as "n-type".

11. The semiconductor material used in devices is doped under highly controlled conditions to precisely control the location and concentration of p- and n-type dopants. A single semiconductor crystal can have multiple p- and n-type regions; the p-n junctions between these regions have many useful electronic properties.

12. SEMICONDUCTORS Semiconductors are the foundation of modern electronics, including radio, computers, and telephones.

13. Semiconductor-based electronic components include transistors, solar cells, many kinds of diodes including the light-emitting diode (LED), the silicon controlled rectifier, photo-diodes, and digital and analog integrated circuits.

14. Increasing understanding of semiconductor materials and fabrication processes has made possible continuing increases in the complexity and speed of semiconductor devices, an effect known as Moore's Law

15. SEMICONDUCTOR MATERIALS Semiconductor materials are nominally small band gapinsulators. The defining property of a semiconductor material is that it can be doped with impurities that alter its electronic properties in a controllable way

16. Most commonly used semiconductor materials are crystalline inorganic solids. These materials are classified according to the periodic table groups of their constituent atoms.

17. Materials A large number of elements and compounds have semiconducting properties, including: • Certain pure elements found in Group IV of the periodic table; the most commercially important of these elements are siliconandgermanium.

18. Binary compounds, particularly between elements in Groups III and V, such as gallium arsenide, Groups II and VI, groups IV and VI, and between different group IV elements, e.g. siliconcarbide. • Certain ternary compounds, oxides and alloys. • A number of organic compounds.

19. An intrinsic semiconductor is made up of one pure element or pure compound. At room temperature, the conductivity of intrinsic semiconductors is relatively low because there are very few charge carriers available.

20. Conductivity is greatly enhanced by a process called doping, in which very small amounts of other elements are added to the intrinsic crystal to create what is called an extrinsic semiconductor.

21. Most common semiconducting materials are crystalline solids, but amorphous and liquid semiconductors are also known. These include hydrogenated amorphous silicon and mixtures of arsenic, selenium and tellurium in a variety of proportions.