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SEMICONDUCTORS

SEMICONDUCTORS. Semiconductor doping and producing P & N material. SEMICONDUCTORS. Pure semiconductor materials contain only a small number of electrons and holes at room temperature, therefore conduct very little current. The conductivity can be increased by a process known as doping.

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SEMICONDUCTORS

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  1. SEMICONDUCTORS Semiconductor doping and producing P & N material

  2. SEMICONDUCTORS • Pure semiconductor materials contain only a small number of electrons and holes at room temperature, therefore conduct very little current. • The conductivity can be increased by a process known as doping. • Doping is the process of adding other materials called impurities to pure semiconductors.

  3. SEMICONDUCTORS • There are tow types of impurities that are added to germanium and silicon crystals. • One of them is a pentavalent material because it has 5 electrons in the valence orbit. • The other is a trivalent material because it has 3 electrons in the valence orbit.

  4. SEMICONDUCTORS Atoms of different types such as Silicon and Oxygen can join together and form Ionic bonds. This is a stable process and a good insulator. Silicon atoms have four valence electrons.

  5. SEMICONDUCTORS Atoms of the same type can join together and form covalent bonds. This is an electron sharing process. Silicon atoms have four valence electrons.

  6. The covalent sharing satisfies the rule of eight. SEMICONDUCTORS In this structure, one bond is formed with each neighbor.

  7. SEMICONDUCTORS This is a silicon crystal It does not conduct because its valence electrons are captured by covalent bonds.

  8. Hole Free electron Thermal carriers SEMICONDUCTORS Covalent bonds can be broken by heating a silicon crystal.

  9. SEMICONDUCTORS The thermal carriers support the flow of current.

  10. SEMICONDUCTORS Heating silicon crystals to make them conduct is not practical!

  11. Free electron SEMICONDUCTORS 5 4 A silicon crystal can be doped with a donor impurity. 1 This is an arsenic atom. Each donor atom that enters the crystal adds a free electron. 2 3

  12. SEMICONDUCTORS The free electrons in N-type silicon support the flow of current. Silicon that has been doped with arsenic is called N-type.

  13. Hole SEMICONDUCTORS 1 This is a boron atom. Each acceptor atom that enters the crystal creates a hole. A silicon crystal can be doped with an acceptor impurity. 2 3

  14. SEMICONDUCTORS The holes in P-type silicon support the flow of current. Silicon that has been doped with boron is called P-type.

  15. SEMICONDUCTORS What are two practical methods of making silicon semiconductor? Free electron Hole (N-type) (P-type) Add a pentavalent impurity. Add a trivalent impurity.

  16. SEMICONDUCTORS Due to heat, it could have a few free electrons. These are called minority carriers. This is a P-type crystal.

  17. SEMICONDUCTORS Due to heat, it could have a few free holes. These are called minority carriers. This is an N-type crystal.

  18. SEMICONDUCTORS Silicon is the workhorse of the semiconductor industry but compound semiconductors help out in key areas. • Gallium arsenide • Indium phosphide • Mercury cadmium telluride • Silicon carbide • Cadmium sulfphide • Cadmium telluride

  19. SEMICONDUCTORS • It is important to remember that N type and P type materials remain neutral even though they have been doped. • N type material has more electrons and P type material has more holes. • Semiconductors conductivity can be increased or decreased by adding more or less impurities.

  20. SEMICONDUCTORS • Remember that semiconductors are poor conductors and poor insulators because they have four electrons in their valence shell. • A good insulator will have three or less electrons in it’s valence shell • A good insulator will have five or more electrons in it’s valence shell

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