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Semiconductor Materials – 1 – 6

26. Recombination of electrons and holes takes place when :

(a) An electron falls into a hole
(b) A positive ion and a negative ion bond together
(c) Avalanche electron becomes a conduction electron
(d) An atom is formed

ANSWER

EXPLANATION

27. Semiconductors are :
(I) Ohmic as they obey Ohm’s law
(II) Bipolar

(a) Only I is true
(b) Only II is true
(c) Both I & II are true
(d) Both I & II are false

ANSWER

EXPLANATION

28. Which of the following statements are correct ?
1. In semiconductor, the mobility of electrons is more than that of holes.
2. In semiconductor, when temperature increases, the resistivity also increases.
3. Metal has positive TCR.
4. In metals, thermal conductivity is inversely proportional to electrical conductivity at constant temperature.

(a) 1, 2, 3
(b) 1, 2, 4
(c) 2, 3, 4
(d) 1, 3, 4

ANSWER

EXPLANATION

29. The carrier mobility in a semiconductor is found to be 0.4 m2/VS. Its diffusion constant at 300 K will be :

(a) 0.43 m2/s
(b) 0.16 m2/s
(c) 0.04 m2/s
(d) 0.01 m2/s

ANSWER

EXPLANATION

30. The Hall coefficient of an intrinsic semiconductor is :

(a) Positive under all conditions
(b) Negative under all conditions
(c) Zero under all conditions
(d) Zero at 0°K

ANSWER

EXPLANATION

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