Properties of Semiconductors - NEET Physics Chapterwise MCQs & PYQs
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NEET Properties of Semiconductors MCQs & PYQs
Practice NEET Properties of Semiconductors Questions
Question 31:
easy
Assertion (A): The temperature coefficient of resistance is positive for p-type semiconductors and negative for n-type semiconductors.
Reason (R): The effective charge carriers in p-type semiconductors are electrons and in n-type semiconductors are holes.
All semiconductors (p-type or n-type) have a negative temperature coefficient of resistance, so (A) is false. In p-type semiconductors, majority carriers are holes, and in n-type, they are electrons. Reason (R) swaps these, so it is also false. Thus, both (A) and (R) are false.
Assertion (A): The probability of electrons to be found in the conduction band of an intrinsic semiconductor at a finite temperature decreases exponentially with increasing band gap.
Reason (R): It is more difficult for the electrons to jump to the conduction band from the valence band if the band gap between them is large.
Assertion (A) is true: The probability of finding electrons in the conduction band is proportional to \(e^{-E_g / (2kT)}\), decreasing exponentially with band gap \(E_g\).
Reason (R) is true: A larger band gap means more energy is required for electrons to jump. Reason (R) correctly explains Assertion (A).
The solids which have the negative temperature coefficient of resistance are:
(2020)
For both insulators and semiconductors, the number density of charge carriers increases exponentially with temperature. This causes their resistance to decrease, meaning they have a negative temperature coefficient of resistance.
Carbon, silicon and germanium atoms have four valence electrons each. Their valence and conduction bands are separated by energy band gaps represented by $(E_g)_C$, $(E_g)_{Si}$ and $(E_g)_{Ge}$ respectively. Which one of the following relationships is true in their case?
(2005)
Carbon in the form of diamond is an insulator with a very large band gap of around 5.4 eV. Silicon and germanium are semiconductors with much smaller band gaps of 1.1 eV and 0.7 eV respectively. Therefore, $(E_g)_C > (E_g)_{Si}$.
At absolute zero, the valence band is completely full and the conduction band is completely empty. At room temperature, thermal energy excites a fraction of electrons from the valence band to the conduction band, leaving holes behind. Thus both bands are partially filled.
A piece of copper and other of germanium are cooled from the room temperature to 80 K, then
(1992)
Copper is a metal (conductor), so its resistance decreases when cooled due to decreased lattice scattering. Germanium is a semiconductor, so its resistance increases when cooled because fewer charge carriers are thermally excited across the band gap.
At absolute zero (0 K), electrons in a semiconductor like Silicon do not have any thermal energy to cross the band gap. The conduction band remains completely empty, making it act as a perfect insulator.
An intrinsic semiconductor is converted into n-type extrinsic semiconductor by doping it with
(2020-Covid)
To obtain an n-type semiconductor, an intrinsic semiconductor must be doped with a pentavalent impurity. Phosphorus is a pentavalent element, which provides extra electrons to act as majority charge carriers.[cite: 1]
For a p-type semiconductor, which of the following statements is true?
(2019)
A p-type semiconductor is formed by doping an intrinsic semiconductor with trivalent impurity atoms. These trivalent atoms create electron vacancies or holes, making holes the majority charge carriers.[cite: 1]