# Microelectronics Questions and Answers – Basic Physics of Semiconductor – Breakdown

This set of Microelectronics Multiple Choice Questions & Answers (MCQs) focuses on “Basic Physics of Semiconductor – Breakdown”.

1. In a one-sided junction, the effect on space charge width, in the n side, due to breakdown can be enhanced by ____________
a) Reducing the permitivity
b) Reduce the electric field below Ecrit
c) Increasing the Acceptor concentration
d) Reducing the Donor concentration

Explanation: The space charge width is inversely proportional to the donor concentration in the n-side. Permitivity cannot be affected while reducing the electric field would degrade the condition of breakdown. The critical electric field for breakdown should be prevalent in the space charge region.

2. From the following graph of Output voltage vs input voltage, determine the source regulation.

a) 17.5%
b) 23.3%
c) 35%
d) Data insufficient

Explanation: To measure source regulation, we have to specify the initial and final values of the input voltage. The given graph doesn’t justify the boundaries of the input voltage and we can find that the source regulation is different for different range of input voltage.

3. D3 has a breakdown of about 6V. Choose the range where D3 will behave as a voltage regulator.

a) 0-10V
b) 10-20V
c) 21-30V
d) 40-50V

Explanation: The minimum voltage required to take D3 to breakdown in 6V. This implies V1 should be at least 36V. Thus the correct range where we can operate D3 as a voltage regulator is 40-50V.

4. If the load (R2) increases, what happens to the minimum voltage to take the Zener into Breakdown?

a) It decreases
b) It increases
c) It remains constant
d) It will double

Explanation: As the load impedance increases, the voltage drop across it increases. For a small input voltage, the Zener diode will be pushed to Breakdown.

5. What happens to the breakdown voltage if the doping concentration decreases?
a) It increases
b) It decreases
c) It remains constant
d) It increases non-linearly

Explanation: The breakdown voltage is inversely proportional to the doping concentration. It will increase with a decrease in the doping concentration. This is because more Electric field is to be produced by the external applied voltage as there aren’t enough impurities.

6. What is the condition to be satisfied for avalanche multiplication?
a) The integration of ionization rate from 0 extending to the space charge region is -2
b) The integration of ionization rate from 0 extending to the space charge region is 1
c) The integration of ionization rate from 0 extending to the space charge region is 2
d) The integration of ionization rate from 0 extending to the space charge region is 0

Explanation: This is a condition used to represent the onset of avalanche breakdown. The ionization rates are strong functions of electric field and the electric field throughout the space charge region is to be defined to evaluate the integral.

7. Breakdown diodes are highly doped.
a) True
b) False

Explanation: This is not necessary since the breakdown voltage is inversely proportional to the doping concentration. We would need low doping to get higher breakdown voltages.

8. How can a breakdown diode help a transistor?
a) Voltage regulator
b) Amplifier
c) Switching
d) Clamper

Explanation: Transistors can be used as voltage regulators. The addition of breakdown diodes with a transistor can be also to make a series voltage regulator. It cannot add to amplification or clamping.

9. Zener breakdown occurs in low doped material.
a) True
b) False

Explanation: Zener breakdown voltage is achieved by low doping. Low doping leads to higher breakdown voltages. The above statement is false.

10. What does the Zener breakdown produce?
a) Electrons
b) Holes
c) Electron-hole pair
d) A few electrons and a lot of holes

Explanation: The Zener breakdown is due to high electric field which leads to the formation of a lot of electrons. Electron-hole pair is formed due to avalanche breakdown.

Sanfoundry Global Education & Learning Series – Microelectronics.

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