Skip to content

Germanium crystal is doped at… (Class 12 Physics 2025, Q9)

questionbuddy.in/q/cbse-12-physics-2025-55-7-1-q9-germanium-crystal-doped-room-temperature

PhysicsCBSE Class 12 · Board exam 2025, set 55/7/1 · 1 mark · MCQ

CBSE Class 12 Physics 2025: question 9

Set in the CBSE Class 12 board exam of 2025, paper 55/7/1, section A, question 9, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q9 · 1 mark · MCQSemiconductor Electronics: Materials, Devices and Simple Circuits

Germanium crystal is doped at room temperature with a minute quantity of boron. The charge carriers in the doped semiconductors will be :

  1. (A)electrons only
  2. (B)holes only
  3. (C)holes and few electrons
  4. (D)electrons and few holes

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 55/7/1.

Hints

Open one hint at a time and try again before the next.

Hint 1

What is the valency of boron?

Hint 2

Remember that thermal generation always produces some minority carriers.

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

  1. Boron is trivalent, so it is an acceptor and the doped crystal is p-type, with holes as majority carriers.

    ½ mark

  2. At room temperature, thermal generation also gives a few electrons, which are minority carriers.

    ½ mark

Answer: Holes and few electrons, option (C)

Where the marks are

  • Identifies p-type: holes majority, electrons minority (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Semiconductor Electronics: Materials, Devices and Simple Circuits, one at a time, marked against the answer key and marking points.Back to the full paper2025 board paper, set 55/7/1: every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.