Characteristics of Semiconducting Diodes - Sultan LeMarc
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Undergraduate theoretical physics presentation on semiconducting diodes and the investigation of I-V characteristics as well as the variation of reverse current as function of temperature. By Sultan ...

Undergraduate theoretical physics presentation on semiconducting diodes and the investigation of I-V characteristics as well as the variation of reverse current as function of temperature. By Sultan LeMarc

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Characteristics of Semiconducting Diodes - Sultan LeMarc Presentation Transcript

  • 1. Characteristics of Semiconducting Diodes By Sultan LeMarc
  • 2. Aims • I-V characteristics of superconducting diodes ▫ Forward bias (Germanium and Silicon) ▫ Reverse bias (Germanium) • Variation of reverse current as function of temperature ▫ Reverse saturation current ▫ Band gap determination
  • 3. What is a semiconductor? • Properties between conductors and insulators • Two types: ▫ Intrinsic ▫ Extrinsic • Smaller energy gap between bands than insulators • Negative and positive charge carriers (Serway, 2010)
  • 4. Doping • Addition of impurities • Adjusts conductivity of semiconductor • Modifies band structure and resistivity N-type P-type • Negative • Positive • Donor atoms • Acceptor atoms • Charge carriers: Electrons • Charge carriers: Positive ‘holes’
  • 5. Diodes • Conducts in only one direction • p-n junction diode: - p junction - depletion region - n junction Germanium (Ge) • Similar to Silicon diode (allaboutcircuits.com) Zener (Ze) • Flow in forward and reverse direction • High reverse resistance • Permanent damage at high reverse current • Avalanche breakdown at sufficiently high reverse voltage
  • 6. Temperature dependence • 0K - all electrons in valance band • Temperature dependence of ▫ Carrier mobility ▫ Carrier concentration • Conductivity increases with temperature ▫ Excitation of electrons across band gap
  • 7. Leakage Current
  • 8. Experiment 1: Forward Characteristics • p-n junction transistors: Si & Ge ▫ Transistors used as diodes – base emitter junction • Independent variable – supply voltage • Dependent variable – current across diode • Restraints ▫ ▫ ▫ ▫ Current < 10mA Voltage < 25V 2.2kΩ resistance to limit current Room temperature (24.7oC) [KCL 2nd Year Physics Laboratory Manual 2012/13]
  • 9. Experiment 1: Results • Disobedience of Ohm’s law • Exponential relationship • Si shows greater conductivity • Forward bias voltage: ▫ Si: 0.7V ▫ Ge: 0.3V • Ge used in low power circuits – more efficient than Si
  • 10. Experiment 2: Reverse Characteristics • Only for Ge ▫ Si reverse current too small to measure with apparatus • Sensitive measuring instruments ▫ Levell multimeter ▫ Digital voltmeter • Supply voltage fixed to ~0.5V [KCL 2nd Year Physics Laboratory Manual 2012/13] • 10µm turn potentiometer used to adjust diode voltage • Dependent variable – current across diode
  • 11. Experiment 2: Results
  • 12. Further Extensions • Different semiconducting materials • Resistance level characteristics • Metal-junction diode: Schottky • Devices: - LED - Photodiode (solar cell) - Thermal diode Photodiode [rapidonline.com]