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Understanding Semiconductor Physics: Conduction Mechanisms and Diode Functionality

Explore the intricacies of semiconductor physics, from electron movement to diode characteristics. Learn about intrinsic and extrinsic semiconductors, thermistors, junction diodes, and rectifiers. Discover how electrons create conductivity and the principles behind forward and reverse bias in diodes. Delve into the fascinating world of electron energy and X-ray generation.

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Understanding Semiconductor Physics: Conduction Mechanisms and Diode Functionality

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  1. The Electron By a Gentleman

  2. - + Conduction • All conduction is due to the movement of free electrons. I’m free In a Semiconductor the electrons are fixed until they receive a little energy

  3. Intrinsic Semiconductors I’m free • Conductivity half way between a conductor and an insulator • Crystals of pure Silica • A photon releases an electron that now can carry current

  4. Extrinsic Semiconductors • These contain doping with atoms of different valency Doping is adding a material of a different valency to increase the conductivity.

  5. Digital thermometer 10°C Ω Water Thermistor Glycerol Heat source THE VARIATION OF THE RESISTANCE OF A THERMISTOR WITH TEMPERATURE

  6. Junction Diode • Near the junction some electrons from the ‘N’ fill the holes in the ‘P’ crystal. P-type N-type

  7. This barrier is called the DEPLETION LAYER Junction Diode • This creates area in the middle where there are no carriers so no conduction P-type N-type

  8. Junction Diode • When the diode is in FORWARD BIAS the depletion layer disappears. The diode conducts. - + P-type N-type

  9. Junction Diode • When the diode is in REVERSE BIAS the depletion layer increases. The diode acts as a barrier or insulator. - + P-type N-type

  10. Diode as Valve • Only allows current in one direction Forward Bias Reverse Bias

  11. Characteristic Curve I/A In reverse Bias No conduction V/v Junction voltage (0.6V) Must be Overcome before Conduction starts

  12. VARIATION OF CURRENT (I) WITH P.D. (V) mA Diode in forward bias + 6 V - V

  13. VARIATION OF CURRENT (I) WITH P.D. (V) A Diode in Reverse bias + 6 V - V

  14. Rectifier • Uses this to turn AC to DC Mains Resistor • This is called half wave rectification

  15. Rectifier • We use a capacitor to smooth the signal to get something more like DC

  16. Thermionic Emission • Electrons leaving the surface of a hot metal e- e- e- e- e- Hot Metal

  17. A N O D E e- High Voltage Cathode Rays • First we heat the cathode to make the electrons jump off by Thermionic Emission We can use a voltage to accelerate the electrons to form a stream C A T H O D E e-

  18. A N O D E e- 2000v Electron Energy • We calculate the energy of each electron first in electron volts EnergyGained = 2000eV C A T H O D E e-

  19. A N O D E e- 2000v Electron Energy • Then we convert this to joules ( Charge on the electron = e = 1.6x10-19 C) Energy Gained = e.V = 1.6x10-19 . 2000 = 3.2x10-16 Joules C A T H O D E e-

  20. A N O D E e- 2000v Electron Velocity • All the energy on an electron must be kinetic energy. Energy Gained = 3.2x10-16 = 0.5mv2 C A T H O D E e-

  21. High Tension Voltage X-Rays • Electrons jump from the surface of a hot metal – • Thermionic Emission Accelerated by high voltage they smash into tungsten Most of the electron energy is lost as heat.-about90% X-rays very penetrating, fog film, not effected by fields.

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