PN Junction and Zener Diode Virtual Experiment

Interactive PN & Zener Diode I–V Experiment

Theory

PN Junction Diode

A PN junction diode is a two-terminal semiconductor device formed by joining a p-type and an n-type semiconductor. At equilibrium, a depletion region forms at the junction, acting as a potential barrier that prevents further carrier diffusion. When an external voltage is applied:

• Forward Bias: The positive terminal is connected to the p-side, reducing the potential barrier. Once the applied voltage exceeds ~0.7 V (for silicon), the diode conducts heavily with an exponential increase in current.
• Reverse Bias: The positive terminal is connected to the n-side, widening the depletion region. Only a very small leakage current (reverse saturation current) flows until the diode reaches its breakdown voltage.

The ideal diode equation is:
I = I_s(e^V/(nV_t) − 1)
where I_s is the saturation current, V is the applied voltage, V_t is the thermal voltage (~25 mV at room temperature), and n is the ideality factor.

Zener Diode

A Zener diode is specially designed to operate in the reverse breakdown region. In reverse bias:

• For voltages below its Zener breakdown voltage (Vz), only a tiny leakage current flows.
• When the applied reverse voltage reaches Vz, the diode conducts heavily but maintains a nearly constant voltage across it.

Thus, Zener diodes are used as voltage regulators. In forward bias, it behaves like a normal PN diode with ~0.7 V threshold.

Procedure

1. Select Diode Type (PN or Zener).
2. Select Material (Silicon or Germanium).
3. Select Bias Mode (Forward or Reverse).
4. Adjust Voltage Sweep Range and Step.
5. Click Generate I–V Table then Plot Graph.
6. Download table (CSV) or graph (PNG) if needed.

Interactive Experiment

Diode Type: PN Junction Diode Zener Diode

Diode Material: Silicon Germanium

Bias Mode: Forward Bias Reverse Bias

Min Voltage (V): Max Voltage (V): Step (V):

Series Resistance (Ω):

IV Values Table

Voltage (V)	Current (mA)

Quick Quiz

1. What happens to the depletion region of a PN junction under forward bias?

a) It widens
b) It narrows
c) It remains unchanged
d) It disappears completely

Answer: b) It narrows

2. What is the typical forward voltage drop for a silicon diode?

a) 0.2 V
b) 0.5 V
c) 0.7 V
d) 1.2 V

Answer: c) 0.7 V

3. In reverse bias, a PN diode conducts:

a) A large current
b) No current at all
c) Only a small leakage current
d) It behaves like a resistor

Answer: c) Only a small leakage current

4. Zener diodes are primarily designed to operate in:

a) Forward bias
b) Reverse breakdown region
c) Saturation region
d) Avalanche region

Answer: b) Reverse breakdown region

5. The Zener voltage (Vz) is:

a) Forward conduction voltage
b) Voltage at which the diode breaks in reverse
c) Zero bias voltage
d) Cut-in voltage

Answer: b) Voltage at which the diode breaks in reverse

6. The diode equation includes thermal voltage Vt which is approximately:

a) 0.7 V
b) 0.1 V
c) 25 mV
d) 1.1 V

Answer: c) 25 mV

7. When a Zener diode is used as a voltage regulator:

a) It maintains constant current
b) It maintains constant voltage across the load
c) It increases resistance
d) It decreases resistance

Answer: b) It maintains constant voltage across the load

8. In forward bias, the current through a diode increases:

a) Linearly with voltage
b) Exponentially with voltage
c) Logarithmically with voltage
d) Does not change

Answer: b) Exponentially with voltage

9. Which diode is more suitable for reverse breakdown operation?

a) Normal PN diode
b) Zener diode
c) Schottky diode
d) LED

Answer: b) Zener diode

10. In the I–V characteristic of a Zener diode, reverse current sharply increases at:

a) Threshold voltage
b) Zener breakdown voltage
c) Cutoff voltage
d) Thermal voltage

Answer: b) Zener breakdown voltage