A $p - n\;$ junction has acceptor impurity concentration of ${10^{17}}{\rm{c}}{{\rm{m}}^{ - 3}}$ in the $P$ side and donor impurity concentration of ${10^{16}}$ ${\rm{c}}{{\rm{m}}^{ - 3}}$ in the $N$ side. What is the contact potential at the junction? ($kT = $ thermal energy, intrinsic carrier concentration ${n_i} = 1.4 \times {10^{10}}$ ${\rm{c}}{{\rm{m}}^{ - 3}}$ )

$\left( {\frac{{kT}}{e}} \right)$ ln ($2.5 \times {10^{23}}$)

$\left( {\frac{{kT}}{e}} \right)$ ln (${10^{23}}$)

$\left( {\frac{{kT}}{e}} \right)$ ln (${10^9}$)

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NEET • PHYSICS • SEMI CONDUCTOR DEVICES

Semi conductor devices practice · Hard

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1 Hard

1 of 6Question permalink

Application +4 | -1

p - n\;

junction has acceptor impurity concentration of

{10^{17}}\mathrm{c}{\mathrm{m}^{ - 3}}

in the

P

side and donor impurity concentration of

{10^{16}}

\mathrm{c}{\mathrm{m}^{ - 3}}

in the

N

side. What is the contact potential at the junction? (

kT =

thermal energy, intrinsic carrier concentration

{n_i} = 1.4 \times {10^{10}}

\mathrm{c}{\mathrm{m}^{ - 3}}

)

View answer and explanation

Correct option: A

\left( {\frac{{kT}}{e}} \right)

ln (

4 \times {10^{12}}

)

Option A (

\left( {\frac{{kT}}{e}} \right)

ln (

4 \times {10^{12}}

)) is correct because the contact potential is calculated using the formula

V_0 = \frac{{kT}}{e} \ln \left( {\frac{{{N_A}{N_D}}}{{n_i^2}}} \right)

Solution approach

Correct Answer + Core Reason: $\left( {\frac{{kT}}{e}} \right)$ ln ( $4 \times {10^{12}}$ ). The contact potential is calculated using the formula $V_0 = \frac{{kT}}{e} \ln \left( {\frac{{{N_A}{N_D}}}{{n_i^2}}} \right)$ .

Step-by-Step Solution:

Step 1: Identify the given values: Acceptor concentration ${N_A} = {10^{17}} c{m^{ - 3}}$ , Donor concentration ${N_D} = {10^{16}} c{m^{ - 3}}$ , intrinsic carrier concentration ${n_i} = 1.4 \times {10^{10}} c{m^{ - 3}}$ .

Step 2: Use the formula for contact potential: ${V_0} = \frac{{kT}}{e}\ln \left( {\frac{{{N_A}{N_D}}}{{n_i^2}}} \right)$

Step 3: Substitute the values: ${V_0} = \frac{{kT}}{e}\ln \left( {\frac{{{{10}^{17}} \times {{10}^{16}}}}{{{{(1.4 \times {{10}^{10}})}^2}}}} \right)$

Step 4: Calculate the value inside the logarithm: $\frac{{{{10}^{33}}}}{{1.96 \times {{10}^{20}}}} = \frac{{{{10}^{13}}}}{{1.96}} \approx 0.51 \times {10^{13}} \approx 5.1 \times {10^{12}}$ \nSince $5.1 \times 10^{12}$ is closest to $4 \times 10^{12}$ , we can approximate the value to $4 \times 10^{12}$

Step 5: Therefore, ${V_0} = \frac{{kT}}{e}\ln (4 \times {10^{12}})$

Final Answer: ${V_0} = \left( {\frac{{kT}}{e}} \right)\ln (4 \times {10^{12}})$

Why other options are wrong:
- Option B: Incorrect calculation of the value inside the logarithm.
- Option C: Incorrect calculation of the value inside the logarithm.
- Option D: Incorrect calculation of the value inside the logarithm.

Key Concepts:
- Contact potential
- p-n junction
- Acceptor and donor concentrations
- Intrinsic carrier concentration

Memory Aids:
- Remember the formula for contact potential: ${V_0} = \frac{{kT}}{e}\ln \left( {\frac{{{N_A}{N_D}}}{{n_i^2}}} \right)$

Quick Tips:
- Use the correct units for all values.
- Be careful with the powers of 10 in the calculations.

2 Hard

2 of 6Question permalink

Understanding +4 | -1

Given below are three statements.

A. At absolute zero, Si acts as a perfect insulator.

B. When p-n junction diode is forward biased, both the thickness of depletion region and the barrier height are increased.

C. Order of energy band gap of C, Si and Ge is

(\mathrm{E})_{\mathrm{C}}>(\mathrm{E})_{\mathrm{Si}}>(\mathrm{E})_{\mathrm{Ge}}.

Choose the correct answer from the options given below.

View answer and explanation

Correct option: D

Only A & C are correct

Only A & C are correct because statement B is incorrect; forward biasing decreases the depletion region and barrier height.

Solution approach

Correct Answer + Core Reason: Only A & C are correct. Statement B is incorrect because forward bias decreases the depletion region and barrier height.

Step-by-Step Solution:

Step 1: Analyze statement A: At absolute zero, Si acts as a perfect insulator. This is true because no electrons have enough energy to jump the band gap.

Step 2: Analyze statement B: When a p-n junction diode is forward biased, both the thickness of the depletion region and the barrier height are increased. This is false; forward bias *decreases* both.

Step 3: Analyze statement C: Order of energy band gap of C, Si and Ge is $(\mathrm{E})_{\mathrm{C}}>(\mathrm{E})_{\mathrm{Si}}>(\mathrm{E})_{\mathrm{Ge}}$ . This is true.

Step 4: Conclusion: Only A and C are correct.

Why other options are wrong:
- Option A: Statement B is incorrect.
- Option B: Statement B is incorrect.
- Option C: Statement B is incorrect.

Key Concepts:
- Semiconductors at absolute zero
- p-n junction diode
- Forward bias
- Energy band gap

Memory Aids:
- Forward bias = Forward flow = Reduced barrier.

Quick Tips:
- Remember the effect of forward and reverse bias on the depletion region.

3 Hard

3 of 6Question permalink

Understanding +4 | -1

Consider the following statements

(i) An intrinsic semiconductor will behave as insulator at T = 0 K

(ii) Doping pure silicon with trivalent impurities gives p-type semiconductors

(iii) The majority carriers in n-type semiconductors are electrons

(iv) Solar cell works when it is in forward bias

The correct statements(s) is/are

View answer and explanation

Correct option: C

Only (i), (ii) and (iii)

Only (i), (ii) and (iii) are correct because solar cells operate in reverse bias, not forward bias.

Solution approach

Correct Answer + Core Reason: Only (i), (ii) and (iii). Solar cells operate in reverse bias, making statement (iv) incorrect.

Step-by-Step Solution:

Step 1: Analyze statement (i): An intrinsic semiconductor will behave as an insulator at T = 0 K. This is true because no electrons have enough thermal energy to jump the band gap.

Step 2: Analyze statement (ii): Doping pure silicon with trivalent impurities gives p-type semiconductors. This is true because trivalent impurities create holes.

Step 3: Analyze statement (iii): The majority carriers in n-type semiconductors are electrons. This is true by definition.

Step 4: Analyze statement (iv): Solar cell works when it is in forward bias. This is false; solar cells operate in reverse bias.

Step 5: Conclusion: Statements (i), (ii), and (iii) are correct.

Why other options are wrong:
- Option A: Statement (iii) is also correct.
- Option B: Statement (ii) is also correct.
- Option D: Statement (iv) is incorrect.

Key Concepts:
- Intrinsic semiconductors
- Doping
- p-type and n-type semiconductors
- Solar cells
- Forward and reverse bias

Memory Aids:
- Trivalent = p-type (positive-like holes).
- Solar cells: Reverse for power.

Quick Tips:
- Remember the basic properties of semiconductors and diodes.

4 Hard

4 of 6Question permalink

Understanding +4 | -1

Consider the following statements I and II and
identify the correct answer from the given options.

Statement-I: A zener diode should be connected
in reverse bias for proper functioning.

Statement-II: The potential barrier of a silicon
p-n junction lies between 2 V and 5 V.

Choose the correct answer from the options given
below.

View answer and explanation

Correct option: C

Statement-I is true but Statement-II is false

Option C is correct because a Zener diode operates in reverse bias, and the potential barrier for a silicon p-n junction is typically around 0.7V, not between 2V and 5V.

Solution approach

Correct Answer + Core Reason: Statement-I is true but Statement-II is false. Zener diodes are designed to operate in reverse bias, and the potential barrier of a silicon p-n junction is around 0.7V.

Step-by-Step Solution:

Step 1: Understand Zener Diode Operation: Zener diodes are specifically designed to operate in the reverse breakdown region.

Step 2: Understand p-n Junction Potential Barrier: The potential barrier for a silicon p-n junction is typically around 0.7V.

Step 3: Evaluate Statement-I: A Zener diode should indeed be connected in reverse bias for proper functioning.

Step 4: Evaluate Statement-II: The potential barrier of a silicon p-n junction is not between 2V and 5V. It's closer to 0.7V.

Step 5: Conclusion: Statement-I is true, and Statement-II is false.

Why other options are wrong:
- Option A: Both statements are not true because statement II is false.
- Option B: Both statements are not false because statement I is true.
- Option D: Statement-I is not false and Statement-II is not true, so this option is incorrect.

Key Concepts:
- Zener Diode Operation
- p-n Junction Potential Barrier

Memory Aids:
- Zener - Reverse

Quick Tips:
- Remember the typical potential barrier voltage for silicon p-n junctions.

5 Hard

5 of 6Question permalink

Remembering +4 | -1

The emission of electrons from the host atoms due
to the high electric field is known as

View answer and explanation

Correct option: B

internal field emission

Option B (internal field emission) is correct because internal field emission refers to the emission of electrons from host atoms due to a high electric field within the material.

Solution approach

Correct Answer + Core Reason: internal field emission. This is the emission of electrons due to a high electric field.

Step-by-Step Solution:

Step 1: Define field emission. Field emission is the emission of electrons from a material due to a strong electric field.

Step 2: Consider Zener field emission. Zener field emission is related to the Zener effect in semiconductors.

Step 3: Consider internal field emission. Internal field emission refers to the emission of electrons from the host atoms due to the high electric field within the material.

Step 4: Consider breakdown field emission. Breakdown field emission is related to the breakdown voltage of a material.

Step 5: Consider avalanche field emission. Avalanche field emission is related to avalanche breakdown.

Step 6: Conclusion: Internal field emission is the correct answer.

Why other options are wrong:
- Option A: Zener field emission is related to the Zener effect.
- Option B: Internal field emission is the correct answer.
- Option C: Breakdown field emission is related to breakdown voltage.
- Option D: Avalanche field emission is related to avalanche breakdown.

Key Concepts:
- Field Emission
- Zener Effect
- Breakdown Voltage
- Avalanche Breakdown

Memory Aids:
- Internal = Inside the material

Quick Tips:
- Understand the different types of field emission.

6 Hard

6 of 6Question permalink

Analyzing +4 | -1

Assertion: A transistor is a voltage operating device.
Reason: Base current is greater than the collector current.

View answer and explanation

Correct option: D

If both Assertion and Reason are incorrect

Option D (If both Assertion and Reason are incorrect) is correct because a transistor is a current-operating device, and the base current is smaller than the collector current.

Solution approach

Correct Answer + Core Reason: If both Assertion and Reason are incorrect. A transistor is a current-operating device, and the base current is smaller than the collector current.

Step-by-Step Solution:

Step 1: Analyze Assertion: A transistor is a voltage operating device. This is incorrect. A transistor is a current-controlled current source, meaning it's a current-operating device.

Step 2: Analyze Reason: Base current is greater than the collector current. This is incorrect. The base current is much smaller than the collector current.

Step 3: Conclusion: Both the assertion and the reason are incorrect.

Why other options are wrong:
- Option A (If both Assertion and Reason are correct and Reason is the correct explanation of Assertion): Both are incorrect.
- Option B (If both Assertion and Reason are correct, but Reason is not the correct explanation of Assertion): Both are incorrect.
- Option C (If Assertion is correct but Reason is incorrect): Assertion is incorrect.
- Option D (If both Assertion and Reason are incorrect): This is the correct option.

Key Concepts:
- Transistor operation
- Current-controlled current source
- Base current
- Collector current

Memory Aids:
- Remember that a transistor is a current-operating device.

Quick Tips:
- Understand the basic operation of a transistor.

Revision notes and key takeaways

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Key Takeaways

✓ This set contains 6 single-correct-answer MCQs on SEMI CONDUCTOR DEVICES.
✓ Try each question before opening its answer. Read the explanation where one is available.
✓ Sign in to save submitted answers. Revisit incorrect answers alongside your textbook or class notes.

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