Characteristics of Semiconducting Diodes
By Sultan LeMarc
Aims
• I-V characteristics of superconducting diodes
▫ Forward bias (Germanium and Silicon)
▫ Reverse bias (Germanium)

• ...
What is a semiconductor?
• Properties between conductors and insulators
• Two types:
▫ Intrinsic
▫ Extrinsic

• Smaller en...
Doping
• Addition of impurities

• Adjusts conductivity of semiconductor
• Modifies band structure and resistivity
N-type
...
Diodes
• Conducts in only one direction
• p-n junction diode: - p junction
- depletion region
- n junction
Germanium (Ge)
...
Temperature dependence
• 0K - all electrons in valance band
• Temperature dependence of
▫ Carrier mobility
▫ Carrier conce...
Leakage Current
Experiment 1: Forward Characteristics
• p-n junction transistors: Si & Ge
▫ Transistors used as diodes – base emitter junc...
Experiment 1: Results
• Disobedience of Ohm’s law
• Exponential relationship
• Si shows greater
conductivity
• Forward bia...
Experiment 2: Reverse Characteristics
• Only for Ge
▫ Si reverse current too small to measure with apparatus
• Sensitive m...
Experiment 2: Results
Further Extensions
• Different semiconducting materials
• Resistance level characteristics

• Metal-junction diode: Schott...
Characteristics of Semiconducting Diodes - Sultan LeMarc
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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 LeMarc

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Characteristics of Semiconducting Diodes - Sultan LeMarc

  1. 1. Characteristics of Semiconducting Diodes By Sultan LeMarc
  2. 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. 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. 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. 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. 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. 7. Leakage Current
  8. 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. 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. 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. 11. Experiment 2: Results
  12. 12. Further Extensions • Different semiconducting materials • Resistance level characteristics • Metal-junction diode: Schottky • Devices: - LED - Photodiode (solar cell) - Thermal diode Photodiode [rapidonline.com]

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