Distinguish between intrinsic and extrinsic semiconductors. Explain how an extrinsic semiconductor is formed by doping, and differentiate clearly between n-type and p-type semiconductors with suitable examples.

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Intrinsic Semiconductors
An intrinsic semiconductor is a pure semiconductor material in its extremely refined form, without any significant impurity atoms added. Examples include pure silicon (Si) and germanium (Ge). Key Characteristics: At absolute zero temperature ($0	ext{ K}$), valence bands are completely filled and conduction bands are completely empty, acting as perfect insulators. At room temperature, thermal energy breaks covalent bonds, generating equal numbers of free electrons and holes ($ne = nh = ni$). Electrical conductivity is quite low at room temperature. Extrinsic Semiconductors and Doping
To improve the electrical conductivity of intrinsic semiconductors for practical electronic applications, a small, controlled amount of suitable impurity atoms is added. This process is known as doping, and the resulting impure semiconductor is called an extrinsic semiconductor. Depending on the type of impurity added, extrinsic semiconductors are classified into two categories: n-Type Semiconductors
An n-type semiconductor is formed when a pure semiconductor (group 14 element like Silicon) is doped with a pentavalent impurity atom (group 15 element such as Arsenic, Antimony, or Phosphorus). Mechanism: Four valence electrons of the impurity atom form covalent bonds with four neighboring silicon atoms. The fifth valence electron is loosely bound and requires very little energy to enter the conduction band, acting as a donor. Charge Carriers: Electrons are the majority charge carriers, and holes are the minority charge carriers. p-Type Semiconductors
A p-type semiconductor is formed when a pure semiconductor (group 14 element like Silicon) is doped with a trivalent impurity atom (group 13 element such as Boron, Indium, or Gallium). Mechanism: The three valence electrons of the impurity form covalent bonds with three neighboring silicon atoms, leaving a vacancy or 'hole' in the fourth bond. This creates an acceptor level just above the valence band, ready to accept electrons. Charge Carriers: Holes are the majority charge carriers, and electrons are the minority charge carriers. Summary Table of Differences: | Feature | Intrinsic Semiconductor | n-Type Semiconductor | p-Type Semiconductor | | :--- | :--- | :--- | :--- | | Purity | Pure form | Doped with pentavalent impurity | Doped with trivalent impurity | | Charge Carriers | $ne = nh$ | $ne \gg nh$ (Electrons majority) | $nh \gg ne$ (Holes majority) | | Conductivity | Low | High | High |

NCERT · Class 12 · Physics · Semiconductor ElectronicsDistinguish between intrinsic and extrinsic semiconductors. Explain how an extrinsic semiconductor is formed by doping, and differentiate clearly between n-type and p-type semiconductors with suitable examples.

1. Intrinsic Semiconductors\nAn intrinsic semiconductor is a pure semiconductor material in its extremely refined form, without any significant impurity atoms added. Examples include pure silicon (Si) and germanium (Ge).

3. n-Type Semiconductors\nAn n-type semiconductor is formed when a pure semiconductor (group 14 element like Silicon) is doped with a pentavalent impurity atom (group 15 element such as Arsenic, Antimony, or Phosphorus).

4. p-Type Semiconductors\nA p-type semiconductor is formed when a pure semiconductor (group 14 element like Silicon) is doped with a trivalent impurity atom (group 13 element such as Boron, Indium, or Gallium).

Summary Table of Differences:

Feature	Intrinsic Semiconductor	n-Type Semiconductor	p-Type Semiconductor
Purity	Pure form	Doped with pentavalent impurity	Doped with trivalent impurity
Charge Carriers	$n_e = n_h$	$n_e \gg n_h$ (Electrons majority)	$n_h \gg n_e$ (Holes majority)
Conductivity	Low	High	High