Question 31:
easyIn semiconductors at a room temperature:
(2004)
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.
Question 32:
easyA 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.
Question 33:
easyAn 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]
Question 34:
easyFor 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]
Question 35:
easyIn a n-type semiconductor, which of the following statement is true?
(2013)
In an n-type semiconductor, pentavalent atoms are added as dopants, making electrons the majority charge carriers. Consequently, holes become the minority charge carriers.[cite: 1]
Question 36:
easyC and Si both have same lattice structure, having 4 bonding electrons in each. However, C is insulator whereas Si is intrinsic semiconductor. This is because:
(2012 Pre)
Carbon's valence electrons are in the second orbit, which is closer to the nucleus and more tightly bound than Silicon's valence electrons in the third orbit. This results in a much larger energy band gap for Carbon, making it an insulator.[cite: 1]
Question 37:
easyIf a small amount of antimony is added to germanium crystal:
(2011 Pre)
Antimony is a pentavalent impurity. Doping germanium with it creates an n-type semiconductor, which has electrons as majority carriers. Thus, there will be more free electrons than holes.[cite: 1]
Question 38:
easyWhich of the following statement is False?
(2010 Pre)
In an n-type semiconductor, electrons are the majority charge carriers and holes are the minority charge carriers. Therefore, the statement that majority carriers are holes is false.[cite: 1]
Question 39:
easyTo obtain a p-type germanium semiconductor, it must be doped with
(1997)
To create a p-type semiconductor, the intrinsic semiconductor must be doped with a trivalent impurity. Among the given options, Indium is a trivalent element, while the others are pentavalent.[cite: 1]
Question 40:
easyWhen arsenic is added as an impurity to silicon, the resulting material is
(1996)
Arsenic is a pentavalent impurity. When added to silicon, it donates an extra electron for conduction, resulting in an n-type semiconductor.[cite: 1]