![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]](https://image.slidesharecdn.com/slideshareversion-131217131626-phpapp01/85/Characteristics-of-Semiconducting-Diodes-Sultan-LeMarc-9-320.jpg)
![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](https://image.slidesharecdn.com/slideshareversion-131217131626-phpapp01/85/Characteristics-of-Semiconducting-Diodes-Sultan-LeMarc-11-320.jpg)
![Further Extensions
• Different semiconducting materials
• Resistance level characteristics
• Metal-junction diode: Schottky
• Devices:
- LED
- Photodiode (solar cell)
- Thermal diode
Photodiode
[rapidonline.com]](https://image.slidesharecdn.com/slideshareversion-131217131626-phpapp01/85/Characteristics-of-Semiconducting-Diodes-Sultan-LeMarc-13-320.jpg)
Characteristics of Semiconducting Diodes - Sultan LeMarc
- 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
- 4. 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)
- 5. 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’
- 6. 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
- 7. 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
- 9. 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]
- 10. 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
- 11. 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
- 13. Further Extensions • Different semiconducting materials • Resistance level characteristics • Metal-junction diode: Schottky • Devices: - LED - Photodiode (solar cell) - Thermal diode Photodiode [rapidonline.com]