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SEMICONDUCTOR

SEMICONDUCTOR. Diodes PN junction and diode biasing. SEMICONDUCTORS. CRYSTAL DIODE. SEMICONDUCTORS. DIODES: NOTE STRIPE AND SYMBOL FOR ANODE AND CATHODE. SEMICONDUCTORS.

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SEMICONDUCTOR

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  1. SEMICONDUCTOR Diodes PN junction and diode biasing

  2. SEMICONDUCTORS • CRYSTAL DIODE

  3. SEMICONDUCTORS • DIODES: NOTE STRIPE AND SYMBOL FOR ANODE AND CATHODE

  4. SEMICONDUCTORS • A type of semi-conductor, simple in construction used for rectification, wave-shaping, circuit protection, and logic operations. • A two terminal device that allows current to flow in one direction, but not the other.

  5. SEMICONDUCTORS • Formed by combining a P-type and N-type semi-conductor materials together. • At this junction the mobile charges in the vicinity of the junction are strongly attracted to their opposites and drift toward each other.

  6. SEMICONDUCTORS • Some of the electrons move across the junction and fill the holes near the junction in the p-type material. • In the N-type material, the electrons become depleted near the junction. • This region is called the depletionregion, and extends only a short distance on either side of the junction.

  7. SEMICONDUCTORS

  8. SEMICONDUCTORS • The opposite charges that build up on each side of the junction create a difference in potential or voltage, referred to as the barrier voltage. • The barrier voltage created at the junction is very small, 0.7 volts for silicon and 0.3 volts for germanium.

  9. SEMICONDUCTORS

  10. SEMICONDUCTORS • When a voltage is applied to a diode, it is referred to as a bias voltage. • Current does not normally flow across the P-N junction, but when just the right voltage is applied using the proper polarity, current will begin to flow. • This is called forward biasing.

  11. SEMICONDUCTORS What is the purpose of the resistor in this diagram?

  12. SEMICONDUCTORS • The negative terminal of the voltage source is connected to the N-type material. • This forces the electrons away from the terminal, toward the PN junction. • The free electrons accumulate on the P side of the junction by the positive terminal.

  13. SEMICONDUCTORS • This action cancels the negative charge on the P side and the barrier voltage is eliminated and current is able to flow. • Current flow occurs only if the external voltage is greater than the barrier voltage.

  14. SEMICONDUCTORS Forward bias: Negative terminal of the battery connected to N side (negative)

  15. SEMICONDUCTORS • Once a current is applied to the diode, a voltage drop occurs. • This voltage drop is equal to the barrier voltage of the diode.

  16. SEMICONDUCTORS • In a forward bias diode the negative terminal is connected to the N-type material and the positive terminal is connected to the P-material. • If the terminals are reversed, the diode does not conduct and is referred to as reverse bias.

  17. SEMICONDUCTORS NOTE THAT NO CURRENT AT JUNCTION REVERSE BIAS

  18. SEMICONDUCTORS • Reverse bias increases the depletion zone, hence increasing the barrier voltage. • No current will flow unless the applied voltage is greater than the break over voltage. • This in turn will cause excessive heat and burn up the diode.

  19. SEMICONDUCTORS • When forward-biased, there is a small amount of voltage necessary to get the diode going. In silicon, this voltage is about 0.7 volts. This voltage is needed to start the hole-electron combination process at the junction.

  20. SEMICONDUCTORS • The operation of the PN junction in a diode is unidirectional since it conducts current in one direction. • When the diode is forward biased, current flows through it freely. • When the diode is reverse biased, current doesn’t flow through it.

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