Difference Between Intrinsic and Extrinsic Semiconductors

Difference Between Intrinsic and Extrinsic Semiconductors

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Rashmi
Rashmi Karan
Manager - Content
Updated on Nov 21, 2023 10:38 IST

The main difference between intrinsic and extrinsic semiconductors is that intrinsic semiconductors are pure semiconducting materials without any intentional doping, while extrinsic semiconductors are intentionally doped to modify their electrical properties. Lets explore some other important differences between these two types of semiconductors.

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A semiconductor is a material with electrical properties between a conductor (like metal) and an insulator (like rubber or plastic). Semiconductors have a unique ability to conduct electricity under certain conditions and act as insulators under different conditions. This property makes them crucial in everything from microchips and transistors to solar cells and LEDs. There are two main types of semiconductors – Intrinsic and Extrinsic. This blog will cover the difference between intrinsic and extrinsic semiconductors. 

Before we dive into the differences between the two types of conductors, let us understand the basics of intrinsic and extrinsic semiconductors.

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What are Intrinsic Semiconductors?

An intrinsic semiconductor is a pure semiconductor material without intentional doping with other elements. A single type of atom forms it, usually silicon (Se) and Germanium (Ge).  

In intrinsic semiconductors, semiconductor atoms have 4 electrons in their outer orbit, which they share with adjacent atoms and form 4 covalent bonds. Thus, each atom has 8 electrons in its outermost shell. This forms a very strong network between atoms and their electrons.

Intrinsic Semiconductors

Fig 1 – The above image shows the structure of an intrinsic semiconductor with all bonds intact at low temperatures. 

Under normal temperature and pressure conditions, an intrinsic semiconductor has an equal number of free electrons and holes (Holes are the empty spaces left by electrons excited to a higher energy band). Free electrons are not attached to any atom and can move freely through the material. 

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Let us understand this with an analogy –

Think of an intrinsic semiconductor like a dough your mother kneaded to make chapatis for your dinner. It’s neutral and hasn’t been altered. Similarly, intrinsic semiconductors are pure semiconductor materials without intentional doping.

What are Extrinsic Semiconductors?

An extrinsic semiconductor is the result of introducing atoms of other elements so that the primitive semiconductor loses its purity and gains in conductivity. This impurification process is known as “doping”. There are two types of extrinsic semiconductors depending on the impurity type added.

Coming back to the dough analogy –

Now, imagine adding salt, spices and oil to that dough. This transformed dough can be used for making dishes other than plain chapatis and represents an extrinsic semiconductor. The added salt, spices and oil change its properties, just as intentionally introduced impurities modify extrinsic semiconductors.

P-Type (Positive Type) Semiconductor

In the P-type semiconductor, trivalent elements with 3 valence electrons are used as dopants. The most common P-type semiconductors are Boron (B), Indium (In), and Gallium (Ga). The four covalent bonds we saw in the intrinsic semiconductor cannot be formed by only contributing three electrons. 

So, these trivalent dopants introduce “holes” into the crystal lattice of the semiconductor material. Because these dopants have one fewer valence electron than the host semiconductor material, they create regions or holes where there is effectively a positive charge due to the absence of an electron.

P-Type Semiconductor

Fig 2 – The figure represents a P-type Extrinsic semiconductor with a trivalent impurity atom of Boron (B) and a void space formed in the covalent bond with a neighboring silicon atom. This hole attracts electrons and participates in conduction.

The network these atoms now make presents a series of holes that allow the movement of electrons more easily, leading to electrical conduction.

Remember – In a p-type extrinsic semiconductor, Number of holes >> Number of free electrons

 

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N-Type (Negative Type) Semiconductor

N-type semiconductor uses pentavalent elements as dopants, with five valence electrons. Phosphorus (P), Arsenic (As) and Antimony are the most commonly used elements in N-type semiconductors. These dopants introduce extra electrons into the crystal lattice of the semiconductor material.

N-Type Semiconductor

Fig 3 – The above image shows the structure of an n-type extrinsic semiconductor. When a pentavalent atom takes the place of a Si atom, all its four electrons bond with four neighbouring Si atoms. However, the fifth electron remains loosely bound to the parent atom.

These extra valence electrons act as majority charge carriers, which means they are the dominant charge carriers responsible for electric current in the semiconductor material. Because they have a negative charge, their movement constitutes an electric current.

Remember – In an n-type extrinsic semiconductor Number of free electrons >> Number of holes 

Difference Between Intrinsic and Extrinsic Semiconductors

  Intrinsic Semiconductors Extrinsic Semiconductors
Doping No intentional doping with impurity atoms. Intentional introduction of impurity atoms through doping.
Type of Atoms Made of a single type of atom (e.g., Silicon or Germanium). Doped with specific impurity atoms –
P-type – Trivalent 
N-type – Pentavalent
Charge Carriers Nearly equal numbers of electrons and holes. The type of doping determines dominant charge carriers.
Conductivity Type Exhibits both n-type and p-type conductivity. Exhibits n-type or p-type conductivity based on doping.
Majority Charge Carriers Electrons and holes have similar concentrations. Either electrons (n-type) or holes (p-type) can be the majority carriers.
Electrical Conductivity Relatively low electrical conductivity. Enhanced electrical conductivity due to intentional doping.
Energy Levels Valence and conduction bands remain relatively close. Energy levels are modified, creating a wider bandgap (doping).
Bandgap Modification The bandgap remains relatively constant. Bandgap can be modified based on the type and concentration of dopants.
Applications Not commonly used for practical devices. Used extensively in electronic devices like diodes or transistors.
Examples Silicon (Si), Germanium (Ge) N-type: Phosphorus (P), Antimony (Sb)
P-type: Boron (B), Indium (In)

Understanding the difference between intrinsic and extrinsic semiconductors is crucial before you learn the semiconductor materials’ applications. We hope this blog was helpful.

FAQs

What is the main characteristic of intrinsic semiconductors?

In intrinsic semiconductors, the number of free electrons roughly equals the number of holes, leading to a balance between these charge carriers.

What is the purpose of doping in extrinsic semiconductors?

Doping introduces impurity atoms to change the concentration of charge carriers and enhance the material's conductivity for specific applications.

How are charge carriers affected in extrinsic semiconductors?

Extrinsic semiconductors have dominant charge carriers based on the doping typeu2014either electrons (n-type) or holes (p-type).

Can intrinsic semiconductors conduct electricity?

Intrinsic semiconductors can conduct electricity due to thermal excitation that generates free electrons and holes, but their conductivity is relatively low.

How does extrinsic doping impact the bandgap of a semiconductor?

Extrinsic doping can modify the bandgap of a semiconductor, affecting the energy levels and allowing for controlled conductivity changes.

Why are extrinsic semiconductors widely used in electronics?

Extrinsic semiconductors with controlled conductivity are the foundation of electronic devices like transistors, diodes, and integrated circuits.

About the Author
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Rashmi Karan
Manager - Content

Rashmi is a postgraduate in Biotechnology with a flair for research-oriented work and has an experience of over 13 years in content creation and social media handling. She has a diversified writing portfolio and aim... Read Full Bio

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