PiTheory

PiTheory JEE Physics Practice & Revision Pack · Class 12 · Chapter 14 · JEE Main

Semiconductor Electronics

Chapter-wise practice and revision for JEE Main: concise notes on intrinsic and doped semiconductors, the p-n junction and diode circuits, Zener regulators, LEDs, photodiodes and solar cells, and logic gates, concept figures, and 49 selected previous-year JEE Main questions covering the major concepts and question patterns, each with a step-by-step solution.

49 selected questions4 topics2 concept figuresPreview · first 3 of 49 questions

How to study this chapter

  1. Look at the topic's figures, then read its notes (5 to 10 minutes). They give the major equations and methods the questions use.
  2. Solve the topic's questions with a timer: 2 minutes for Easy, 3 to 4 for Medium and Hard.
  3. Check the solution. Read the Point to note line even if you were right: it is the idea you will reuse.
  4. Mark each question Got it or Revise. Come back to the Revise list after two days.

Where the marks come from

Main idea of each of the 177 previous-year JEE questions in the PiTheory bank

Logic gates56
Special diodes43
p-n junction29
Semiconductors10

Contents

  1. 1Intrinsic and extrinsic semiconductorsQ1–Q8
  2. 2p-n junction and diode circuitsQ9–Q18
  3. 3Special diodes: Zener, LED, photodiode, solar cellQ19–Q37
  4. 4Logic gatesQ38–Q49
  5. ✓Last-day checklist
01

Topic 1 · Q1–Q8

Intrinsic and extrinsic semiconductors

10 of the 177 JEE PYQs in the bank test this as their main idea

Quick notes

$$n_en_h=n_i^2,\qquad \sigma=e(n_e\mu_e+n_h\mu_h),\qquad \rho=\frac1\sigma$$

Band gap: conductor $\approx0$, semiconductor $\sim1$ eV (Si $1.1$, Ge $0.7$), insulator $>3$ eV. Heating creates more pairs, so resistance falls (negative temperature coefficient).

TypeDopantMajorityFermi level
intrinsicnone$n_e=n_h$mid-gap
n-typepentavalent (P, As)electronsnear conduction band
p-typetrivalent (B, Al)holesnear valence band
  • Doped crystals stay electrically neutral.
  • Mobility $\mu=v_d/E$.
Trap. n-type is not negatively charged.

Practice: first 3 of 8 questions

Q1JEE Main 2023 (31 Jan, Shift 1)Easy

The effect of increase in temperature on the number of electrons in conduction band ($n_e$) and resistance of a semiconductor will be as

  1. ABoth $n_e$ and resistance decrease
  2. BBoth $n_e$ and resistance increase
  3. C$n_e$ increases, resistance decreases
  4. D$n_e$ decreases, resistance increases
Answer and solution

Answer: Option C: $n_e$ increases, resistance decreases

Concept. Heat breaks more covalent bonds, freeing more electrons into the conduction band; more carriers means lower resistance.

Answer. $n_e$ increases, resistance decreases (Option C).

Point to note. More carriers.

Q2JEE Main 2021 (26 Aug, Shift 1)Easy

**Statement I:** By doping silicon semiconductors with pentavalent material, the electrons density increases.

**Statement II:** The $n$-type of semiconductor has a net negative charge.

In the above statements, choose the most appropriate answer from the options given below:

  1. ABoth Statement I and Statement II are false.
  2. BStatement I is true but Statement II is false.
  3. CStatement I is false but Statement II is true.
  4. DBoth Statement I and Statement II are true.
Answer and solution

Answer: Option B: Statement I is true but Statement II is false.

Concept. A pentavalent dopant gives a spare electron, so $n_e$ rises. But each donor atom that gives up an electron becomes a positive ion: the crystal stays neutral.

Answer. Statement I true, II false (Option B).

Point to note. Still neutral.

Q3JEE Main 2025 (4 Apr, Shift 2)Medium

Consider an n-type semiconductor in which $n_e$ and $n_h$ are the numbers of electrons and holes, respectively.

(A) Holes are minority carriers

(B) The dopant is a pentavalent atom

(C) $n_en_h \ne n_i^2$

(D) $n_en_h \ge n_i^2$

(where $n_i$ is the number of electrons or holes in the semiconductor in its intrinsic form)

(E) The holes are not generated due to the donors

Choose the correct answer from the options given below:

  1. A(A), (C), (D) only
  2. B(A), (C), (E) only
  3. C(A), (B), (E) only
  4. D(A), (B), (C) only
Answer and solution

Answer: Option C: (A), (B), (E) only

Concept. In n-type material electrons are majority carriers from pentavalent donors; holes come only from thermal pair generation, and the mass-action law $n_en_h=n_i^2$ still holds.

Step 1. Check. A true; B true; C false; D false (it is equal); E true.

Answer. (A), (B), (E) only (Option C).

Point to note. $n_en_h=n_i^2$.

46 more questions and 3 more topics in the full chapter

  1. 2p-n junction and diode circuits10 questions with solutions
  2. 3Special diodes: Zener, LED, photodiode, solar cell19 questions with solutions
  3. 4Logic gates12 questions with solutions
  4. ✓Last-day checklist

The complete Semiconductor Electronics chapter is in the Class 12 Pack and the Complete Pack, as a PDF on WhatsApp. Want to see a whole chapter first? Laws of Motion and Current Electricity are free in full.

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