p-n Junction Diode - UNSOLVED PRACTICE SET
Chapter: Semiconductor Electronics | Topic: pn Junction Diode
P-N JUNCTION DIODE - UNSOLVED PRACTICE SET
Topic: pn Junction Diode
Multiple Choice Questions
Q1. A p-n junction is formed by:
- Joining two metal wires
- Joining a p-type and an n-type semiconductor
- Joining two insulators
- Joining a conductor and an insulator
Q2. The depletion region in a p-n junction is formed due to:
- Movement of electrons from the p-side to the n-side
- Diffusion of majority carriers across the junction and recombination
- Application of external voltage
- Heating of the junction
Q3. The potential barrier across an unbiased silicon p-n junction is approximately:
- 0.1 V
- 0.7 V
- 2.0 V
- 5.0 V
Q4. The width of the depletion region in an unbiased p-n junction depends on:
- The doping concentration on both sides
- The temperature only
- The area of the junction only
- The external voltage only
Q5. In the depletion region of an unbiased p-n junction:
- There are many free charge carriers
- There are immobile ions and very few free charge carriers
- The concentration of electrons equals the concentration of holes
- The semiconductor behaves like a conductor
Q6. The electric field in the depletion region of an unbiased p-n junction is directed from:
- p-side to n-side
- n-side to p-side
- Random direction
- There is no electric field
Short Answer Questions
Q7. What is a p-n junction? Explain how it is formed.
Q8. Explain the formation of the depletion region in a p-n junction. What are the charge carriers in this region?
Q9. What is the potential barrier in a p-n junction? Why does it form?
Q10. Draw the energy band diagram of an unbiased p-n junction and label the depletion region and potential barrier.
Q11. Why is the depletion region also called the depletion layer or space charge region?
Q12. How does the width of the depletion region change when the doping concentration is increased?
Long Answer Questions
Q13. Explain the formation of a p-n junction with suitable diagrams. Describe the processes of diffusion and drift that lead to the formation of the depletion region and the potential barrier.
Q14. Draw the energy band diagram of an unbiased p-n junction. Explain how the energy bands bend at the junction and how this bending is related to the potential barrier.
Q15. Discuss the factors affecting the width of the depletion region and the height of the potential barrier in a p-n junction. How do doping concentration and temperature affect these parameters?
Numerical & Application-based Problems
Q16. A silicon p-n junction has acceptor concentration N_A = 10²² m⁻³ on the p-side and donor concentration N_D = 10²¹ m⁻³ on the n-side. The intrinsic carrier concentration is n_i = 1.5 × 10¹⁶ m⁻³.
(a) Calculate the built-in potential (barrier potential) at 300 K.
(b) Calculate the width of the depletion region on the p-side.
(c) Calculate the width of the depletion region on the n-side.
(d) Calculate the total width of the depletion region.
Q17. The depletion capacitance of a p-n junction is given by C = εA/W, where W is the depletion width.
(a) For a junction with area 1 mm² and depletion width 1 μm, calculate the capacitance.
(b) If the reverse bias voltage is increased, the depletion width increases to 2 μm. Calculate the new capacitance.
(c) Explain why this voltage-dependent capacitance is useful in varactor diodes used in tuning circuits.
Q18. In your school electronics lab, a student is studying p-n junction characteristics.
(a) She connects a silicon diode in forward bias and measures the current at different voltages. At what minimum voltage does she expect significant current to flow? Explain why this 'knee voltage' exists.
(b) The student then connects the diode in reverse bias and measures a very small current (microamperes). Explain the origin of this reverse saturation current and why it is temperature-dependent.
(c) She learns that a solar cell is essentially a large-area p-n junction. Draw a diagram showing how light generates electron-hole pairs in the depletion region and how the built-in electric field separates them to create a voltage.
(d) A classmate suggests that a p-n junction could be used as a temperature sensor. Explain the physics behind this idea and why the forward voltage drop of a diode decreases by about 2 mV per °C rise in temperature.
(e) In India, solar panels are being installed on millions of rooftops under government schemes. Explain why silicon p-n junctions are used in these panels and what factors affect their efficiency in the Indian climate.